Concrete Repair 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

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.



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.



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.



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

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.”  


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 or visit For more details about epoxy injection, visit:

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