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