Concrete Repair Posts

John Bors

Recent Posts

Crack hiding tips (following epoxy injection)

Posted by John Bors on Tue, Apr 29, 2014 @ 12:04 PM

Can you make epoxy injection repaired cracks in concrete disappear? This is a difficult challenge, but you can take steps to reduce their visibility.

Architectural precast panel manufacturers as well as many concrete repair contractors have developed several techniques when a new surface coating is not the answer.

If the localized area around the crack is stained (from water leaks or dirt deposits), high pressure water blasting or light sandblasting might be the first thing to try. Be careful to avoid altering the surface texture or exposing the aggregate below the surface paste. An alternative stain removal procedure is to use a mild acid micro etch applied on the concrete surface. Although there are proprietary products formulated for this purpose, some specialists swear by a combination of dilute acetic acid (vinegar) and 1 % dish soap which can be sponged and scrubbed into the surface, allowed to soak and then rinsed off.

Assuming the crack requires epoxy injection, be sure to special order a non-tinted resin/hardener combination from us. Normally, our part B (hardener) of the epoxy injection resins is slightly tinted to help provide visual evidence that both components are delivered in proper proportions by the metering pump during crack injection.

ChemCo Systems StripSEAL™ is a great choice for a peelable (easily removed) surface seal (also callestripseal, removal epoxy injection surface seald capseal). It cures quickly and readily strips without leaving a residue. Occasionally, there may be a slight darkening of light surfaces—this can be fixed with a light application of dilute acetic acid as described above.

If the crack is relatively wide (you be the judge), you can pre-place a strip of 1/4” masking tape completely over the whole crack before sealing with StripSEAL. This prevents the StripSEAL from penetrating into the crack walls and allows the injection resin to fill to the level of the surface. This minimizes the shadow created by the indented seal. If masking tape is used, you will have to puncture it at the locations of each surface port in order to connect with the crack.

In concrete crack repair projects where appearance and esthetics are especially critical, you can try a modified dry sack technique. First, you will need to locate some of the smaller (fine) aggregate (suggested max. size 40-50 mesh) used in the original concrete mix or a similarly colored facsimile. Strip the seal no more than 30 minutes after the injection resin has gelled (long before cure, but while the epoxy is still tacky). Then take a small burlap sack filled with the small aggregate and dust the area of the crack until the still tacky glue line is covered. Or the dry aggregate can be scrubbed over the surface using a soft sponge rubber float. The fine aggregate should match the color of the surface and fill in the shadow of the crack as the fine grains are held in place by the tacky epoxy.

For large areas, or surfaces with other defects including bug holes, it may be more convenient to use a wet sacking or parging mix which contains Portland cement, fine aggregates and other admixtures similar to the constituents of the original concrete finish. Prior to performing this type of repair, it is highly recommended to practice on a small mockup placed in a non-visible location.

For more help, call us at ChemCo Systems (800-757-6773).

Tags: peelable injection seal, concrete crack repair epoxy, cracked concrete repair, concrete crack repair

Polyureas vs Epoxies for Floor Control Joints

Posted by John Bors on Wed, Apr 23, 2014 @ 18:04 PM

Polyureas vs. Epoxies razor slicing polyurea for control joint

Polyureas are now a popular choice for filling and repairing control joints on commercial, industrial and warehouse floors, as well as some public areas where high heels or skate wheels cross joints. In the good old days, semi-rigid epoxies were more widely used. Which product is better?

At ChemCo Systems, we don’t have a favorite because we make a selection of both products. To choose, consider the intended use of the facility and the application environment.

Control joints are typically filled for several reasons: a) protect the integrity of the joint (reduce joint nose spalling), b) safety, c) reduce maintenance costs and d) prevent accumulation of foreign debris. The choice of the polymer may relate to the the type of traffic that uses the floor.

       

Polyurea Control Joints

Cure speed is the most desirable feature as often the filled joint can often be opened to traffic within 1-2 hours or sooner. Since time is money and finishing the floor is one of the last steps prior to opening, the faster cure speed of the polyurea is often the most valuable benefit.             

Because of very fast gel times, it is may be impractical to hand-mix the faster curing polyureas, so using a special pump such as our Model C may be useful on very large jobs for high production rates.              polyurea metering pump

Unlike epoxies, polyureas can cure in very cold conditions, in some cases as low as -25°F. In fact, polyureas are used frequently to fill joints in large freezer floors while the freezer is in service. At this low temperature, an epoxy is dormant and will likely freeze. Usually, an epoxy will cure when the ambient air increases to 40°F or more.              

Polyureas are often touted for their greater elongation capability (up to 200%+ vs. ~90%). Yet neither material is intended for use in joints designed to move (such as expansion joints). However, the tall proportional cross-section of most control joints causes either material to separate from the side wall if there is significant joint movement because neither can stretch across its thick middle.

Though polyureas are generally softer, they are very tough under abrasive conditions. Tested in a standard Taber test rig, they may exhibit 40% less weight loss after 1000 cycles than control joint epoxies.              

A cautionary note—use an epoxy primer with a polyurea when in doubt about dampness or moisture. The isocyanate portion of a polyurea reacts very quickly with moisture and this interaction may decrease the performance of the cured polymer or cause gassing or foaming.

 

Epoxy Control Joints 

Although generally slower curing, this may be an advantage if the crack filling is done by hand pouring or a bulk caulk gun because of longer working time.              

When the substrate is damp, wet, or contaminated, an unprimed epoxy has a better chance of bonding to the sides of the joint than a high speed polyurea.              

In exterior applications, UV exposure causes fading and sometimes chalking of an epoxy. With aromatic-type polyureas often used in control joints, there can be significant color changes caused by sunlight which may be cosmetically unappealing.              

When it comes to mixing and tolerance for “eye-balling” the A & B components, epoxies are more forgiving. Polyureas may lose some of their properties as soon as the mix ratio is off by 3-6% or more, whereas epoxies will often cure when the proportions are even further apart.              

Most semi-rigid epoxies are harder  (higher durometer) than comparable polyureas. This may be a critical factor in uses when there is high point loading across floor joints such as the steel wheels on some pallet jacks.              

Both product types are relatively chemical resistant, but the epoxy usually has a slight edge with organic solvents, many acids and some oxidizers and sanitizers used on floors such as bleaches.

Both products can be blended (extended) with carefully selected aggregates or natural sands for deep repairs. Please ask for our help if this option is of interest. It's most important to use only dried sands containing less than 0.2% moisture by weight for either binder.

If you can‘t decide , call us (800-757-6773) for friendly technical assistance and the best selection anywhere. We're usually in the office by 6:30 and out by 5:00 California time.

Tags: floor joint repair, control joint filler, rapid cure polyurea, floor joint filler, fast set polyurea

StripSEAL™ tips: Epoxy Injection made quicker, easier and cleaner

Posted by John Bors on Tue, Apr 15, 2014 @ 18:04 PM
StripSEAL for epoxy crack injection

Probably the most popular surface seals for epoxy injection are pastes based on epoxy formulations. StripSEAL is different than epoxy surface seals since it is based on polyurea technology, but the trouble is, some field technicians use it the same way as an epoxy, which usually causes frustration. If your field techs are open-minded and do a couple of things differently, they will usually be very happy with its performance--otherwise it wouldn't be one of our biggest selling products every year.

The 4 biggest reasons why people use StripSEAL: 1) it peels off easily, 2) it's fast-curing even in cold weather, 3) it doesn't ever crack when left overnight and 4) it doesn't stink. Plus it is not regulated as hazmat for shipping so it can be sent by any means and is not considered corrosive.

For manufacturers of architectural pre-cast panels or gfrc panels, StripSEAL is immensely popular for the same reasons as above, but especially because it doesn't stain or require some sort of abrasive removal that could disfigure the surface appearance.

We offer Stripseal in bulk and in cases of dual cartridges and and if you click on the link you will find the product data sheet.

 

Preference Ratio:

I don't know if you typically prefer StripSEAL in cartridges or bulk, but we sell about 5:1 the volume with cartridges preferred. Why? The convenience factor and also the cartridges aid in achieving the proper proportional ratio. As a polyurea, getting very close to the proper 1:1 ratio is more critical for StripSEAL than for epoxies. In fact, some of our customers buy in the cartridges but throw away the static mixers--they just use the cartridge for correct proportioning onto a mixer board where they mix just the right amount by hand.

 

Manual Gun:

An aid in achieving the proper ratio is a good dual component gun. After trying about 10 different models over the years, we finally found a patented manual gun made in the US that is extremely good at 2 critical actions: 1) excellent ratio control and 2) excellent product acceleration throughout the grip squeeze action. The patent covers the use of a special spring-action, which aids both items by applying residual pressure and leverage beyond that which the hand is capable of. The gun is a bit trickier to work with for very short runs because you need to release the lock on the spring to take all of the pressure off the plungers when you don’t need more material.

 

The best bet for large jobs is an electric or air driven gun because they generally are very heavy duty, get the best ratio and provide instant acceleration of product through the static mixer, which helps eliminate unmixed material spots that don’t cure properly. These guns don’t get tired like operator hands so the first cartridge gets mixed at the same high speed as the last cartridge.

 

Mixing:

If you buy StripSEAL in bulk, it must be ratioed very close to 1:1 or it won't work consistently. Some people use spoons or small paper cups to get the volume correct. After you get equal volumes, you must mix it for about 30 seconds after you first start to observe the uniform gray color. The extra mixing helps compensate for the fast reaction time, which means that you get a good color before it is actually mixed sufficiently.

 

If you use cartridges, a good dual-component gun like the model we sell, is essential. Bad guns don’t provide sufficient mechanical advantage (you need at least 4--5:1 ratio) in their squeeze grip to allow the instantaneous acceleration through the static mixer that helps eliminate unmixed and less than sufficiently mixed material.

 

Partial cartridge:

If you use a cartridge straight through until empty without stopping, you'll get the best performance. If you must stop more than 2 minutes halfway through the cartridge, you will either need to remix the first couple of static mixer quantities on a piece of cardboard with a trowel or simply throw it away. This semi-mixed material in and immediately behind the static mixer is partly reacted already and won't set up properly without further manual mixing due to the high reaction speed of the polyurea.

 

Pressure:

We usually suggest that injection pressures be kept below 150 p.s.i. for StripSEAL (the lower the better). See also time, surf. prep. and blowout topics below.

 

Time:

You can usually inject within about 35-40 minutes after applying StripSEAL, but if you are going to use higher pressures (>100 p.s.i.), then wait an hour or more after seal application.

 

Surface prep:

StripSEAL has a peel strength up to 400 psi so it should be able to withstand relatively high pressures assuming you leave sufficient thickness on the surface to offset its flexibility. If your surface is relatively smooth, you should roughen it with a very mild grind or wire brush to give it some teeth or a slightly roughened profile.

 

Surface ports:ChemCo epoxy injection surface port

If instead of taped ports, you use glued-on surface ports, you will need to apply the StripSEAL more thickly around the base of the port than with epoxy because it is more flexible and if too thin will allow a bit of weeping. Some ports (particularly the cheaper ones molded of polyethylene) are extremely flexible themselves and don't stick well to anything. Epoxies work better with these only because the epoxy is rigid. ChemCo surface ports are made of nylon and work fine with StripSEAL, but in some applications you may need to support them with wire, a toothpick or a cocktail straw.

 

Blowouts and Stripping:

Many field techs apply epoxy seals very thinly. StripSEAL is ineffective if applied this way. It will blow out under higher pressures due to its flexibility. We suggest that for good containment and easy removal, StripSEAL be applied at a minimum of 1/8" thick and about 1" width.

 

If you are getting lots of well sealed areas with a few pesky blowouts, there are three likely causes: 1) poor ratioing, 2) insufficient mixing when applied or 3) applied too thinly.

 

Best use of cartridges:

If you ever get a very large job in the thousands of feet where StripSEAL can be of help, we advise purchasing an air-driven gun. We have found that the acceleration though the static mixer is very fast and uniform on the air-driven equipment and this factor helps mix the StripSEAL much more efficiently.

 

Wet substrate:

StripSEAL doesn't perform well on damp or wet substrates. The iso “A” side wants to react with the water and as a result doesn't always bond as well. Epoxies should be used under these conditions unless you can get the surface temporarily dry with a hot air gun. Moisture after application doesn't affect the seal.

 

Sorry about the length of this message, but I hope it helps you get improved performance out of a unique timesaving and laborsaving product. Please call or write us at ChemCo Systems if you need more information on concrete repair epoxy or epoxy protective coatings for concrete.

Tags: peelable injection seal, concrete crack repair, removable surface seal, epoxy surface seal

10 Things Not to do with Concrete Repair Epoxy

Posted by John Bors on Thu, Aug 2, 2012 @ 13:08 PM

 

1.      Leave Large Quantities of Mixed Epoxy in Bulk

concrete repair epoxyEpoxies that cure at room temperature generally give off heat (are exothermic) when the two components react. Most products if mixed in quantites as small as a pint will heat up to as much as 450°F (this includes hardware store products). So, if you need a large quantity of epoxy adhesive or coating, mix only what you can use within the potlife and plan to place it on the substrate as soon as possible.

 

If the epoxy in bulk is not used quickly, the generated heat can be enough to boil the epoxy and some products will generate smoke and possibly ignite as well as melt a plastic pail. Should this occur, you can add dirt or sand to the hot epoxy to cool it down and prevent additional smoke—be careful!

 

2.      Use wet aggregate

If you want to add aggregate (or sand) to epoxy to make a mortar or grout, use aggregate that contains less than 0.2% moisture. Don’t use sand that was stored in a loose pile that could contain excess moisture or the strength and properties of the mixed grout can be negatively impacted.

 

3.      Mix with a stick

Two component epoxies require adequate sheer in order to properly react. With some lower viscosity products, a rotary paint mixing blade on a drill is fine. For higher viscosity epoxy coatings or pastes, a “Jiffy” type mixer is strongly recommended as it will provide shear without adding excessive air to the mixture.

 

4.      Use wrong proportions

Most epoxies can tolerate off-ratio proportions to 5% and some epoxies will cure with higher off-ratio mixes. To be safe, stay within 5%. Most professionals who mix epoxies by hand will purchase either disposal plastic measuring cups to ensure proper proportions or on critical projects will weigh each component separately. If you elect to weigh the components, check the proper amount of A and B as the weight ratio is often much different from the volume ratio.

 

5.      Apply epoxies wearing a t-shirt, shorts and sandals

The minimum proper personal protection equipment (OSHA term is PPE) for mixing epoxies generally includes eye protection (safety glasses, face shield or goggles), skin protection (rubber gloves, long sleeves and pants). In most jurisdictions, there is also a requirement to have an eyewash station available within less than a minute from the location of the work.

 

6.      Apply epoxies to dirty or contaminated substrate

Most professionals know that taking a shortcut on surface preparation can ruin a project. Attempting to adhere to concrete, wood or steel that has oil contamination is foolhardy and the bond will likely fail in use. Discuss the issue of contamination with your supplier and he will provide the best way to prepare for the application. In most cases, a slight removal of the surface with a grinder or shotblast with some roughening (similar to 40 mesh sandpaper) is a preferred approach.

 

7.      Apply epoxy over a moving crack or joint

When repair epoxies or protective epoxy coatings are used on concrete (particularly in exterior applications), the concrete will expand and contract linearly in relationship with temperature. This means that cracks or cold joints will become smaller as the concrete temperature increases and larger when the concrete temperature decreases. In some climates, the daily temperature cycle is as much as 40°F or more. In these locations, the crack will move a considerable amount each day and the repair material will crack almost immediately.

 

8.      Store epoxy overnight in pickup truck or outside in cold weather

If the nighttime temperature is expected to fall below 40°F, the epoxy stored in the truck will be cold. It will cure very slowly and also be much thicker and difficult to mix properly. In cooler seasons, store epoxy as close to 73°F as possible prior to use. In some cases, professionals will intentionally “condition” their epoxy by storing it at an elevated temperature so that it will cure faster and be easier to mix especially in cold weather applications.

 

9.      Place neat epoxy in large voids

For the same reasons as stated in item #1, epoxies in large masses can become very hot to the point where the epoxy is damaged. If it is necessary to repair a large void, consult your manufacturer for his recommendations. One solution to prevent damage from epoxy exotherm is to mix aggregate with the epoxy which lessens the exotherm effect as most of the mass is in the aggregate. We offer several low exotherm products (a low viscosity liquid epoxy and a paste epoxy) which are especially designed for this use.

 10.  Purchase the exact quantity

With the high costs of delays, manpower, shipping and mobilization, most professionals purchase excess materials for their project. For coatings, often a 15% safety factor is used and for other concrete repairs or restorations with epoxy, the factor can be 5-10%. We offer a great estimator tool and you can preset the safety factor to account for accidental losses and unforseen quantity needs (exact measurements on construction projects are never exact which is why they are often called estimates).

Please call or write us at ChemCo Systems if you need more information on concrete repair epoxy or epoxy protective coatings.

Tags: epoxy repair tips, concrete repair epoxy, epoxy coatings

Stitching for Structural Concrete Repair

Posted by John Bors on Tue, Jul 31, 2012 @ 18:07 PM

stitching with epoxyAfter concrete is placed in service, unforeseen uses or conditions can affect its performance or cause damage, especially across cold joints or control joints. If the overload or temporary condition is excessive, new cracks can form and there can be displacement of the crack or joint. A few examples include temporary weight overloads, poor subsurface compaction or soils, changes in water tables, subsidence and changes in use. Damages resulting from these changes must be repaired and the repairs may include additional strengthening in the concrete restoration or repair project.

Is there a simpler, low cost method to provide additional support to existing structures?

Yes, the non-proprietary procedure is a related to steel plate bonding and it is commonly called rebar stitching. It may often be an efficient alternative to glass or carbon fabric wrapping, but since no company is actively marketing it, often the structural engineer or architect doesn’t even consider it. The repair is often fast, inexpensive and requires no special tools. And the procedure stands the test of time: the pictoral diagram is from an old US Army Corp of Engineers concrete restoration design from the early 1960's.

Installation is straightforward. First, it is critical to know the depth of coverage (and possibly the location) of the existing reinforcing steel so that the old reinforcement is not damaged during the installation of stitches (note that some concrete is unreinforced so this concern may not exist). The location of structural steel is listed on the orginal design drawings. The architect or engineer calculates a requirement for increased strength, estimates a safety factor and then develops a pattern of steel or FRP reinforcing bar to be installed. The contractor saw cuts channels at specified depths in the concrete surface, ties the bar together at intersections, then fills the channel with a structural liquid epoxy or paste epoxy adhesive. If the channel lies on a horizontal deck, the filling is by gravity, otherwise the channel may need to be sealed with a temporary overlying form so the epoxy paste or liquid can be pumped into the hollow space. Unlike fiber wrapping systems, dowel holes can be drilled in any direction to better anchor the bar placed in the surface channels and the bar can cross the joint or crack at any angle. CCS Bonder Liquid LWL and CCS Bonder Paste LWL are two structural epoxy adhesives frequently used for this application.

What type of repair might qualify as a candidate for rebar stitching? Parking and bridge decks, slab on pan floors, locally overloaded areas, missing or insufficient rebar, anchoring large patches and spall repairs to sound concrete, beams and piers all might be excellent stitching applications. Stitching benefits include: a) fast installation, b) localized repairs, c) low material and labor costs, d) no special equipment required, e) damp and wet substrates are OK and f) repaired surface can bear traffic.

Call or write us if you need an adhesive recommendation or more practical tips for stitching.

Tags: stitching, epoxy concrete repair, concrete repair

Litigation and Structural Concrete Repair

Posted by John Bors on Fri, Jun 29, 2012 @ 13:06 PM

litigation concrete repair scales of justiceIt’s an unfortunate fact of building construction that legal disputes can occur.  When a claim involves a major structural defect or the partial failure of a building, litigation is often unavoidable.  But it doesn’t take a catastrophic incident for attorneys to become involved and for matters – not to mention time and costs – to quickly escalate and get out of hand.  Legal action can be initiated by the mere presence of cracks in concrete – whether those cracks are structural and pose a real risk or are cosmetic and no real threat to the structure.    

“Owners can confuse minor cosmetic cracking with a major structural issue and may seek legal remedies,” said Pete Barlow, a principal at Contech Services Inc., a company that repairs, strengthens and waterproofs concrete structures.  “That’s why it’s necessary early in the process to bring in experts that can accurately assess structural cracks to determine their significance and the available remediation options before jumping to conclusions.” 

According to Barlow, such a team would include a structural, or forensic, engineer as well as a concrete repair specialist.  Barlow extends the team one step further by bringing in a representative from ChemCo Systems, a company specializing in epoxy solutions tailored to specific structural concrete situations.  In many cases, repairs using advanced epoxies eliminate the need for concrete removal and replacement. 

Epoxy Injection Repair of Concrete Cracking

Where possible, such teams should be assembled long before the lawyers take over. In the structural concrete field, the old saying that an ounce of prevention is better than a pound of cure very much applies. When cracks are detected, then, it is always safer to call in professional assistance to determine whether the cracking is structural or non-structural.

“Structural cracking in support beams, columns and load bearing areas is of particular concern,” said Dr. Wolfgang Eisenhut of ChemCo, a polymer chemist with 40 years of experience in understanding the physical properties of various resins and how to blend them to achieve maximum strength and cohesion.  “Non-structural cracks are not detrimental to building integrity, though they may need to be addressed due to cosmetic reasons or to take proactive steps to prevent those cracks from growing over time and eventually reaching the structural stage.”

Another issue is the location and orientation of cracking. Those running in random directions are of lower priority than those in beams, columns or other load bearing areas. Closely spaced cracks or repetition of cracking at the same locations on each floor should be viewed as a warning sign of looming structural problems.  

Before things escalate into the legal arena, therefore, preventive concrete remediation using high performance crack injection epoxies manufactured for structural concrete bonding and crack repair can keep costs down while satisfying the demands of the owner. 

Barlow points out that while many different types of epoxy are available, one size does not fit all.  It requires the right combination of materials, chemistry and expertise.  For this reason, Contech has worked with ChemCo Systems for almost two decades. ChemCo specializes in making two component structural epoxies and application equipment designed for concrete structural repairs.

“Their chemists understand the physical properties of the various resins and how to blend them to ensure the job is done right,” said Barlow.

Barlow gave the example of a dispute where one party insisted that concrete be demolished and redone. The engineer isolated the problem and Barlow brought in ChemCo as a single source of equipment, material and expertise for a broad line of resins. ChemCo’s chemists studied the environment and formulated a custom epoxy to structurally bond extensive cracking. When the owner’s engineer reviewed that plan, he agreed that it created a usable and functional structure with long life expectancy. All parties then consented to implement this as a safe and cost-effective solution.

“Bringing in veteran forensic engineers and conducting remediation with advanced epoxies is a smart way to eliminate the need for concrete replacement and to avoid costly litigation,” says Barlow.  

Dealing with the Specter of Litigation

gavel concrete restorationDespite proactive attempts to address owner concerns, sometimes legal action is unavoidable. And in the event of construction defect litigation, repair contractors have to tread carefully, noted T. Daniel Heffernan, an attorney with the Heffernan Law Group inSeattle. A construction defect lawyer for 25 years, he cautions that concrete remediation work requires special expertise.

In defect claims, for example, it can be a challenge to allocate liability for repair costs. Extensive documentation is required. This entails use of detailed cost codes for tracking labor time and material and other costs. Reason: a settlement or damages award often allocates repair cost damages to various parties responsible for the defects, including the general contractor, the concrete subcontractor or supplier and the steel installation subcontractor or fabricator. Not all contractors and their employees are experienced at providing such detailed documentation.

“It is also vital to work with a knowledgeable forensic engineer,” said Heffernan. “The engineer is the hand and the contractor is the tool. Although complimentary, these roles are distinct.”

On a project subject to litigation, the repair contractor’s job is to closely follow the engineer’s instructions. Further, contractors have to be adept at documenting building conditions as they investigate the defects and undertake repairs.  That means before and after photos, and precision documentation of locations and work performed so that experts who were not present can understand the nature and extent of each defect, why it needs to be repaired, as well as the overall scope of repair.

Repair contractors and their staff can run into trouble, too, if they try to assume the role of the forensic engineer and state opinions about the causes of the defects. One side or the other can latch onto these comments and the repair contractor’s credibility and independence can be compromised.

“Offhand comments by the repair contractor can jeopardize claims as the other side might try to use such unqualified remarks in support of arguments to shift or avoid liability,” said Heffernan. “If you work in this area, you need to be mindful of the litigation aspects of the work, as well as of the repair work itself.”

Contractor Responsiveness

Barlow said that contractors sometimes cause themselves legal problems by failing to accept that someone is dissatisfied. Instead of understanding owners concerns, they brush it off or refuse to cooperate. “Litigation polarizes the parties involved,” he said. “If they can settle it after a lengthy legal battle, why not get there first via face-to-face discussion?”

Based on his 35 years of experience, Barlow thinks it is best to try to resolve matters through dialogue in the early stages. “It is wise to be responsive to owner requests,” said Barlow. “Contractors delayed or negative reactions can make owners feel the only avenue is to sue.”

For more information, call (800)-757-6773 or fax (650)-261-3799. E-mail is email@chemcosystems.com; visit www.chemcosystems.com

Tags: legal aspects of concrete repair

We offer the "how-to's" of Concrete Restoration

Posted by John Bors on Mon, Jun 25, 2012 @ 16:06 PM

epoxy stone restorationWe are an employee owned corporation formed in 1993. Our founders were six previous technical managers of Adhesive Engineering (AE), a pioneering company in the development of epoxies for use in both aerospace and civil engineering. When AE was sold and integrated into another company, ChemCo Systems was created to provide the highest performance polymer products and responsive technical service for applications in concrete repair, protection and restoration.

Use of two component structural epoxies in conjunction with automatic metering epoxy pumps to repair concrete started in 1959. At the request of Pacific Gas & Electric, two AE managers traveled in a station wagon to the Sierras to attempt repairs of cracked concrete in a hydroelectric dam. They brought some liquid epoxies and some pumping equipment and attempted to inject a mixture into spalled and cracked areas of the dam. They failed on their initial attempts to correct the problem but were invited back several months later and were successful in the repairs. The concrete was sampled by drilling cores and subsequent tests proved that it could be restored to its original monolithic strength with this innovative civil engineering repair. An extensive and costly demolition and reconstruction of portions of the dam was avoided.

Epoxy Solutions for Concrete Repair

We sell epoxies used for civil engineering infrastructure applications. More specifically, we focus on delivering solutions for concrete repair, protection and restoration to North American and international customers. Our customers include concrete repair specialists, general contractors, industrial manufacturers, utilities, state DOTs, airports and universities.

As a separate product line, we manufacture the world’s top performance paving, called Epoxy Asphalt (EA). Independent testing by universities in the US and Asia including Rutgers, the University of Texas, South China University in Guangzhou and Southeast University in Nanjing confirm that EA outperforms all other driving surfaces in fatigue performance which is a lifespan predictive factor for long span bridges which use lightweight (and flexible) orthotropic steel decks. In the last 10 years, EA has been placed on over 30 bridges in China and several other Asian countries including the longest oversea bridge in the world, the Qingdao Bay Bridge, and the longest main span cable stay bridge, the Sutong Bridge. We have local technical staff for Asia based in Tianjin, China; however, all of our products are manufactured in the U.S. and exported to Asia in sea containers.

Structural Concrete Repair Focus

There are several large companies that provide a broad range of construction related chemicals. ChemCo’s primary focus is repairing concrete used in structural applications. We serve this select niche through our approved applicator program, offering facility owners the assurance that this group of specialty contractors has undergone training at our headquarters and uses an integrated complete system of products and equipment from a single source (ChemCo). Instead of offering one or two of everything across all categories of products, we offer 6-10 choices of performance leading products in a select category such as epoxies for crack injection.

Third party engineers, architects and consultants will state that we are very patient in responding to unique repair challenges in all types of structures. Our reputation is based on our company culture which emphasizes our experience and integrity: most of our customers (many who have been with us for more than one generation of their ownership) know we will send them to the best alternate source if we can’t provide an in-house product solution. We’re happy to help with writing a repair specification, consult on the merits of alternate technical approaches or even create a test and custom product to fill a one-time need. 50% of our staff is an engineer or scientist. Rarely a customer who calls for information will be transferred more than one time.

Our reputation is partly based on producing the highest performance products in our specialized categories. We have not received a single return of product for quality or performance reasons since our facility moved to our current location in Redwood City in 1998. We emphasize safety in all departments and have not had a lost time accident since our founding in 1993. Our products are all 0 VOC and contain no solvents or toxics.

Repair epoxies for Re-purposing

A continuing trend of property owners is to make efficient use of existing facilities and waste less. Buildings and structures are more commonly recycled, reused, repurposed or rehabilitated than ever before. This trend is international; even China with its incredible growth, has created strong regulations which favor repurposing structures over the expedient option of demolition and starting over. Examples of building or facility repurposing where ChemCo has provided product solutions are:

  • Conversion of a multi-story warehouse to a data centerepoxy repair concrete column

  • Conversion of an old Folger coffee roasting plant to class A office space including seismic upgrades

  • Improving the foundation of a hospital to handle more load so additional stories could be added to the building

  • Conversion of a former Hubbell Electric motor manufacturing plant to a conference center seating 5500 for Living Free Ministry

  • Conversion of a paint manufacturing plant to a charter high school

Concrete Repair Case Histories

  • Holy Name Cathedral, Chicago A structural engineering survey found that many of the wooden timbers used to support the roof were marginal in load capacity. Steel dowels and our epoxy products were used to provide improved structural performance and fill checks and voids within the timbers. Some of voids had substantial volumes so a special low exotherm epoxy was used to avoid problems with overheated epoxy and shrinkage stresses.

  • Ochsner Hospital, New Orleans A custom epoxy was formulated to rebond concrete pile caps supporting the building that had large shrinkage faults caused in part by the exotherm of the concrete curing in bulk.

  • Fenway Park, Boston The dugout tunnels are partially located below the water table and players had to walk through puddles to get to the locker room. We provided an underwater rated epoxy injection resin and surface seal that cured at low temperatures so the work could proceed over the winter.

  • Stanford Green Library, CA Houses a rare book collection in basement. Concrete and tile floor on main level had excessive fine cracks which could potentially leak either during cleaning or if fire sprinklers went off on first floor. We provided ultra low viscosity epoxy healer/sealer to permanently penetrate and seal fine cracks with no discoloration.

  • Holcim Cement, CO One of the largest cement manufacturing plants in the US had challenges with concrete quality in their silo structure. We provided on-site training and high temperature resistant structural repair epoxies (extreme performance not offered by any other manufacturer) in this award winning repair.

  • SEPTA, Philadelphia This was a multiyear structural repair of elevated lightrail track and its supporting concrete. Special epoxy specifications were to withstand vibration during operation while the adhesive was curing. 

  • Denver International Airport Due to difficult geotechnical issues with underlying soils, runway slabs were subjected to undue movement and stress and required repair soon after construction. ChemCo injection resins surpassed the engineering requirements and restored the slabs to original monolithic strength. Pavement problems are a very critical item for airports as FOD (foreign object debris) can cause engine failure.

  • San Francisco Int’l Airport Similar challenge as DIA encountered except in terminal area slabs. We helped with construction specifications and supplied products to splice together slabs so they would not be displaced. No airport operations were affected and the terminal gates were available to the carriers each day.

  • Foxwoods Resort, CT One of the largest parking decks in the U.S., consisting of 500,000 square feet, had minor surface cracks and imperfections on the four decks (3 elevated). A yearlong product evaluation was conducted to identify a product which could heal the small cracks without altering the appearance and protect from spalling and future freeze/thaw damage and corrosion of the internal steel. ChemCo’s Epoxy Healer/Sealer was selected for the project which was performed over 2 summers so disruption of service could be minimized.

  • Chicago highrise The exterior cladding was composed of marble facing attached to precast concrete using steel pins. Over time, the panels were suffering from delamination and separation caused by water intrusion and freeze/thaw expansion. There was concern a panel skin could separate and cause damage on the sidewalk below. One of ChemCo’s experienced applicators worked with the building engineers to re-bond the panel skins using a ChemCo epoxy to the underlying concrete and eliminate any hollow gap between substrates.

  • Siemens LA Metro and other light rail systems  After a frustrating search for a system to apply over the metal floors of the electrical control stations of Siemens engineered light rail power control systems, we worked with one of our applicators in Houston to develop a non-conductive semi-flexible built up epoxy aggregate seamless floor with extreme durability.

  • Pacoima and Big Dalton dams LA area Subsequent to earthquake activity nearby these large reservoirs, engineering inspections determined that water leakage in enlarged cold joints could lead to weakening of the structure. So the reservoir levels were ordered to be lowered by more than 50% until repairs could be effected. ChemCo’s unique very long life epoxy with low exotherm was selected so it could travel long distances within the dam to help seal and repair joints.

  • Condo highrise A newly constructed condo highrise in San Jose was designed with a multilevel parking deck below grade. With a winter season rise in the water table after several years of drought, the two lower levels of deck were flooded prior to the opening of the building. Pumps were brought in to help lower the trapped water while an epoxy injection specialist patiently located nearly invisible cracks and areas of internal defects in the walls of the parking decks to inject them with a permanent underwater epoxy. Following a 3 week effort, the pumps were no longer needed and the walls were dry.

  • Colorado pipeline A concrete lined fresh water supply pipeline had been in active service for 40+ years. Its lining on the bottom was suffering from erosive damage by the sands that were transported as sediment. ChemCo was asked to provide a toughened, wear resistant mortar as well as a hard coating to ensure the integrity of the lining for years to come. All materials could contain no VOCs or flammable components.

  • Alamodome, San Antonio, TX An engineering inspection revealed that the original cementitious grout protecting the unique cable anchorages (the exterior cables are key architectural features) had shrunk exposing the connections to possible corrosion. A contractor was hired to restore the internal anchorages and requested that we formulate a low modulus polymer with no shrinkage and very long mixlife at high temperatures. ChemCo responded with a product (to replace a Euro material unavailable in the U.S.) in less than 2 weeks.

  • Dial Soap (part of Henkel Corp) New Jersey A manager who operates a 24/7 facility producing sanitizing products needed a highly chemical resistant coating to protect pipe trenches. He wanted to apply the system in very cold temperatures (below where most coatings can be used) and the substrate would be wet. We provided a two product combination utilizing a primer that can be applied under water and would cure very quickly despite nasty conditions. He called back saying he was surprised at the performance and ease of use and is now a repeat customer.

Gold Standard for Customer Service in Concrete Restoration

We are a responsive company focused on all aspects of customer service. About 85% of orders are shipped same day. We understand that many of our specialty contractors and their customers are under tremendous time pressure to perform a critical repair overnight, over the weekend or between shifts so our shipping department is adept at last minute deliveries—whether by truck, ocean, air or courier. No caller waits on hold very long and you will get straight yes or no answers from us. Our technical personnel have been with the company for 25 years on average so we generate conservative, experienced and field-tested advice. We don’t hesitate to direct a customer elsewhere if there is a better alternative product.

All of our Kemko certified applicators are required to have trained with us (at no charge) and offer their customers a complete single source system so there is no finger pointing between manufacturers in the event of a problem. We replace critical epoxy injection pumps of our applicators every 6 years to avoid aged failing equipment in the field. Our contractor customers remain with us for long periods—many are in their second or third generation of ownership.

With formulation, testing and engineering experience dating back to the late 1950’s, we have likely solved most challenging concrete restoration applications previously and can access these records quickly for reference. We encourage our customers to challenge us with unusual applications, extreme environments, difficult repairs and custom formulations. ChemCo product development, product testing and manufacturing is located under the same roof so information is shared quickly between departments. ChemCo owns and operates its own physical, chemical and environmental testing equipment and can simulate most extreme product applications without incurring the delays of outsourcing—our ability to formulate new products or evaluate difficult application conditions is not delayed by external testing.

Most of our competition sells primarily through distributors. We sell most of our product directly. As a result, we can offer the efficiency of direct shipping without an intermediary and related cost savings. If there is a critical need for technical support, our customer knows he can get it right the first time by calling us without having to work through channels. We won’t compromise on making product switches for convenience or merely because of excess stock of the wrong item.

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Tags: concrete restoration case histories

When do you need a professional for Concrete Crack Repair?

Posted by John Bors on Tue, Jun 19, 2012 @ 19:06 PM

concrete crack repairConcrete cracks. It’s a fact of life. Some cracks might not need attention while others could have serious structural consequences. How can you tell the difference?

 “It is important to accurately assess structural cracks to determine what is significant and what is not,” said John Duntemann, a principal at consulting engineering firm Wiss, Janney, Elstner Associates (WJE). “You have to properly identify the extent and cause of cracking before you can implement the right repair solution.” 

Cracks in concrete might be caused by a number of factors such as thermal expansion and contraction, sub-grade settlement, the loads being applied and even earthquakes. This all adds up to internal and external stress that manifests as large and small cracks.   

In many cases, however, there is uncertainty as to what to do about cracks.  Pete Barlow, a principal at Contech Services Inc., a company that repairs, strengthens and waterproofs concrete structures, said his company is constantly being contacted by anxious building managers and owners. “Many times a week, people send us photos of cracking at their facilities asking for advice,” said Barlow.  

Concrete Crack Classification

There are various methods of classifying cracks in concrete. One primary way is to split them into two groups: structural and non-structural. Structural cracking affects the integrity of the building. Cracking in support beams, columns and load bearing areas is of particular concern. 

Non-structural cracks, on the other hand, are not detrimental to building integrity, though they may need to be addressed due to cosmetic reasons, if there is water leakage or to take proactive steps to prevent those cracks from growing over time and eventually reaching the structural stage. Tiny fractures can also lead to other challenges. 

“Small cracks in below grade foundation walls can allow water to migrate into the structure,” said Barlow. 

Width, length and depth of the cracks are another consideration. Hairline cracks are generally not a problem, but it depends on where they are. A high frequency of them, though, could indicate an underlying stress issue that needs to be addressed.  But as the size of openings increases, so should the concern. As a rule of thumb, cracks larger than 0.015 inches or larger,” said Barlow, should be investigated. “The larger the width, the greater the likelihood you have lost aggregate interlock,’ said Barlow. “But repairs can be done on cracks down to 0.005 inches.” 

A third issue is location/orientation. Cracks in random directions are of lower priority than those in beams, columns or other load bearing areas. “If one side of the fracture is offset from the other, that is often a bad sign,” said Barlow. “Other warning signs are closely spaced cracks or repetition of cracking at the same locations on each floor.” 

Concrete Repair Epoxy

In many cases, epoxy injection is used as the optimum technique for concrete crack repair. Although there are many epoxy types and uses, high performance epoxies manufactured for structural concrete bonding and crack repair are the focus here. 

concrete crack repair aDuntemann gives the example of cracking that appeared in a cooling tower being constructed at a synthetic fuel plant. Cracking developed at the ends of pre-stressed concrete beams.  Demolishing the structure and starting over was not considered an option. Management brought in WJE to find an alternative. “The beams were injected with epoxy and load tested to verify their structural capacity,” said Duntemann.  

In another case, WJE was retained to investigate large cracks in the concrete caps that sat on top of concrete pile foundations. “We developed a method of reinforcing the pile caps and injected an epoxy into the cracks to reconnect the fragmented caps,” said Duntemann. 

Water, however, presented a further challenge – the epoxy had to deal with a saturated environment. WJE requested help from ChemCo Systems’ team of chemists. They formulated an epoxy that could fill three quarter inch cracks and cure in the presence of water. ChemCo specializes in making two component structural epoxies and application equipment designed for concrete structural repairs, including at industrial plants, bridges, stadiums and parking decks to name a few. 

“You often run into challenging environments such as cracks full of water, cold temperatures or exceedingly wide cracks that require a customized solution,” said Duntemann. “The ChemCo Systems staff is very knowledgeable about epoxy in general and their own products in particular, and the environment in which these products are applied. We typically identify potential products, and consult with the manufacturer like ChemCo Systems for advice on the product application.” 

Contech Services, too, has worked with ChemCo Systems for almost two decades. All field personnel have been thoroughly trained in the use and application of ChemCo Systems epoxy resins and equipment for structural repair. 

“Their chemists understand the physical properties of the various resins and how to blend them to ensure the job is done right,” said Barlow. “We prefer ChemCo Systems as it acts as a single source of equipment, material and expertise for a broad line of resins. Most major manufacturers have two or three resins at best. ChemCo Systems has about a dozen so when you run into something unique, they know which one or which mixture is best suited.”  

Summary

Building owners noticing cracks, then, are advised to contact a structural engineer to assess the extent of the damage. They can help determine whether or not it is a significant issue. 

“As building owners are typically not engineers, they are advised to retain a licensed structural engineer who can evaluate concrete cracking,” said Barlow. He also advises against a do-it-yourself approach for all but the most minor problems. In his view, there are too many factors involved in the engineering and chemical formulation side to leave anything to chance. 

“When a problem is identified, it is important to retain professionals with experience solving these problems,” said Duntemann. “The correct solution to a problem requires a good understanding of the cause of that problem.” 

For more information, call (800)-757-6773 or fax (650)-261-3799. E-mail is email@chemcosystems.com or visit www.chemcosystems.com. For more details about epoxy injection, visit: http://chemcosystems.com/pdfs/crack_injection_for_concrete_crack_repair.pdf

Tags: concrete crack repair, concrete repair epoxy, epoxy injection

Consider Lifecycle Costs for Concrete Restoration or Replacement

Posted by John Bors on Fri, Jun 15, 2012 @ 11:06 AM

It seems obvious on the surface that repair or restoration of cracked or spalled structural concrete in a stadium, parking deck, bridge, tunnel, dam, dock or runway will reduce ownership costs. But if the underlying damage is severe, it may be more cost effective to tear down and rebuild.

A critical element in this evaluation is an assessment of overall lifecycle costs. This is the time-honored method to determine the best course of action with regard to structural concrete repairs. By considering all aspects of the financial equation, an owner can achieve a fuller understanding of available options. Spending a little more today to fix an immediate problem correctly may considerably reduce the total cost of the structure over its lifespan.

“Life cycle costs (LCC) are cradle to grave costs summarized as an economic model of evaluating alternatives for equipment and projects,” said H. Paul Barringer, P.E. of Barringer & Associates. Inc. “The objective of LCC analysis is to choose the most cost effective approach from a series of alternatives to achieve the lowest long-term cost of ownership.”

Concrete Condition Survey epoxy plus steel for seismic upgrade

Identifying unseen conditions and the extent of damage is a key element in any LCC evaluation. Non Destructive Testing (NDT) is often used by engineers to obtain detailed structural information. NDT techniques include sounding, galvanic pulse testing, ground penetrating radar and in-situ load tests. When more upfront condition detail is available, the engineer can prepare a more accurate remedial cost estimate and it is less likely the owner will face costly change order surprises should he elect a repair option.

A huge repair bill may tilt the balance towards replacement as is the case with some older hospitals in California where state regulations require emergency buildings to meet current more stringent earthquake codes. A major healthcare provider in Los Angeles, for example, recently demolished two large buildings erected around 30 years ago and is rebuilding. The high cost of improving the structural elements of these facilities to meet current seismic standards was one of several factors which led management to select the replacement path.

In some cases, replacement may prove to be the better option for an older structure with only a few years left before the design life ends. In all instances, it is prudent to hire an engineer for a structural lifecycle evaluation and condition survey. If the damage is not disruptive to the entire structure, often the best option is to repair.concrete spall repair testing

Take the case of San Francisco Airport, which has taxiway lights embedded in concrete structures. When the concrete collars for these lights began to fail, the airport tried a quick setting cementitious repair material which failed to eliminate the problem. Faced with a live heavily used aircraft taxi lane, it considered all options for further repair or complete replacement. In this case, it chose a proven solution capable of being injected in harsh loading conditions: a customized epoxy formulated specifically to cope with the difficult working conditions and without compromising concrete integrity. “The ChemCo epoxy stabilized our taxiway lights and eliminated further deterioration,” said Charlie Freas, a civil engineer at San Francisco International Airport. “This proved to be the right decision in the long term, both financially and structurally.”

The airport has since used similar epoxy formulations to repair cracking in parking structures, service tunnels below groundwater level, and the airport’s light rail system, as well as for concrete spalling on taxiway aprons and ramps.

With regards to pavement concrete spall repair, the airport is constantly inspecting its runways, aprons, and the surrounding concrete infrastructure for any signs of degradation in order to avoid flying object damage (FOD) which can cause catastrophic damage to jet engines. “As concrete spalling can be substantial at times and the consequences so significant, we would rather replace an entire concrete section than be faced with the possibility of having to buy a new airplane engine,” said Freas. “However, we have confidence that effective epoxy spall repairs provide the flexibility and strength to support our planes without further spalling.”

Factors to Consider for Concrete Restoration

Freas pointed out that lifecycle costs may not be the only factor to take into account when it comes to the repair versus replace question. In some instances, the airport needs to realign a runway or change the grade, at which point all associated concrete areas may be completely removed and replaced.

concrete crack repairSimilarly, the Port of Oakland in California has to look beyond the subject of lifecycle costs for certain structures. One tenant, for instance, utilized an 80-year-old wharf complex for container crane operations. While the wharf clearly needed to be rebuilt, the port had no temporary site available. Repair was the only possibility.

Another time a tenant dropped a 60-ton piston from a height of 100 feet onto a wharf resulting in severe damage. In this case, lifecycle costs favored repair. The port harnessed epoxy injection for concrete crack repair of the wharf deck and soffit (underside). “I’ve inspected the wharf below sea level and the ChemCo Systems customized epoxy prevented any corrosion of the rebar, returned the structure to its original strength and extended its lifespan,” said Bill Morrison, Manager of Harbor Facilities for the Port of Oakland. “After many years, these wharves are still operating as designed.”

Repurpose for Changing Times

A recent fast-growing trend is to find and adapt new uses for vacant buildings or structures that have remaining useful life. Governments world-wide are passing new regulations and may offer monetary incentives to recycle or adaptively reuse existing buildings rather than choosing demolition. This is already happening widely in the U.S. where the practice is often referred to as brownfield redevelopment. In China’s large cities, owners are rewarded with financial incentives if they agree to convert an old hotel into condos or an aging office structure into a warehouse. Several former parking decks have been transformed into computer server farms in Beijing after exterior shells were revamped.

This repurposing trend for existing buildings is a high growth element of the sustainable construction movement and is beginning to eclipse new construction in urban areas of North America due to architectural preservation, environmental and waste disposal concerns.

 Whether you elect to repair, restore or replace concrete, do it right, select the correct materials and consult an engineer who can help you evaluate your options from a lifecycle perspective. Call or email us at ChemCo Systems if you need help with concrete restoration, repair or protection.

Tags: cracked concrete repair, concrete restoration, runway epoxy, concrete spall repair

Baby carrots, F-16's and flexible epoxy

Posted by John Bors on Wed, Jun 13, 2012 @ 12:06 PM

What do F-16’s, F-18’s and baby carrots have in common? They have all landed on CCS Binder Patch, Nosing, Slurry (PNS) which is our low modulus (flexible) epoxy.F 18 lands on flexible epoxy

PNS is our most popular binder for use in repairing control joint nosings and spalls, often located in very tough applications like Navy and Air Force runways, municipal refuse handling facility floors, large vehicle repair shops, machine shops and even food processing grinding wheels.

These days, it is very popular to reuse old concrete floors in some buildings that have been repurposed from industrial use to retail or commercial. The control joints in the old floor often need repair or rebuilding. To accomplish the joint repair, a horizontal section is cut out on each side of the joint and a plastic piece is placed in the old opening as a block out, then a PNS-based grout or polymer concrete extended with aggregates is poured or troweled into the new slots on both sides of the joint.

Most of the time, PNS is extended with 4-5 volumes of gap graded aggregates to provide a durable (5000 psi) surface that is highly resistant to chipping, impacts, point loads and large temperature swings. When used as an extended binder, it has a useful working life of up to 45 minutes at 72°F, so there is time to properly place the entire batch you just mixed. It should be noted that a mortar mixer is the best way to obtain the shear needed for optimum blending of aggregates although some contractors use a rotary 5 gal pail mixer with a scraper blade. If the aggregate extension is not extreme and the application is small, a Jiffy mixer can be used in a pinch. Just don’t use a cement mixer—it does not generate sufficient shear to properly wet out the aggregates.

PNS is a very good substrate wetting binder and will bond to damp and even completely saturated concrete. It will also adhere to steel, wood, FRP and many elastomers and is ideal for bonding flexible materials to concrete. For best results, ensure that the substrate surface has no contaminants and preferably is roughened to the texture of 40 mesh sandpaper.

flexible epoxy polymer concreteWhat is the role of the aggregates? Depending on the size distribution, shape, hardness and quantity used, they can dramatically affect the placement properties, strength, wear, impact resistance and thermal behavior of the grout. Because the material is flexible and is extended, it will tolerate deeper placements than more rigid epoxy polymer concretes. It’s possible to achieve workable mixes that are only ~10% epoxy with excellent trowelable properties or you can use a slightly lower quantity of aggregates and obtain self leveling. Unlike cementitious patches, there’s rarely a bonding problem and in most cases, priming isn’t necessary. Note that it is critical that the aggregates are dry and should have less than 0.2% moisture. Please call us if you need some advice on locating the best aggregates locally—it is far more cost effective if you buy the aggregate this way rather than shipping a low cost heavy material around the country.

So what’s the deal about baby carrots? Well, we can’t reveal secrets of our best customers. We can tell you that baby carrots are formed from larger carrots that have been cut and ground. The longest-lived grinding wheels are made with a high mod epoxy and a low mod epoxy in a special combination. Similar wheels handle even harder tasks like pistachio nut hulls.

Tags: spall repair, low mod epoxy, low modulus epoxy, flexible polymer concrete, concrete overlay, concrete patch, flexible epoxy