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 called 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).