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

Injection Ports for Concrete Crack Repair

Posted by John Bors on Fri, Jun 8, 2012 @ 16:06 PM


Do you always consider alternative porting methods as you prepare to execute an epoxy crack injection repair project? 

Maybe not. Yet the method selected by your field technician may make a significant difference in the quality, linear footage productivity and job profitability. Many crack injection specifications intentionally leave this option to the practical experience and judgment of the concrete repair contractor.

With a goal of filling a crack with epoxy quickly, neatly, and completely, several factors to consider are:


  • Crack width and substrate thickness
  • Application temperature and moisture
  • Orientation (ceiling, wall or floor)
  • Gross linear footage
  • Access limitations
  • Surface appearance after repair
  • Average time duration on port
  • Choice of surface seal material (epoxy vs other)

 Many of our concrete restoration contractors use a combination of several porting methods:

     Taped surface ports 

Stripseal-removable-seal-for-epoxy-injectionLow cost ports are established as gaps in the surface seal with quarter inch masking tape applied at the proper interval prior to the surface seal. The tape is pulled before the seal hardens completely. With hand pressure, the injection mix head directly contacts the open gaps left by the tape though a compressible rubber grommet or rubber tip such as our part # B07 which is available in two sizes (see last image below). After the port is filled, soap or wax is manually rubbed over the crack to seal the port. Some of the long time specialty concrete repair contractors insist that this method is the most efficient practice for most crack injection projects. This method is illustrated in the top image for use on an industrial floor and in the second image (to the left) in conjunction with our peelable surface seal StripSEAL.

     Rubber tips, pins, wire, (finishing) nails, straws, golf tees and toothpicks 

These alternatives to tape often require no drilling. Sometimes they are used in combination. For example, rubber tips (such are our part # B07-3 or B07-12) can be located along the crack with toothpicks, (or pins or nails) prior to the seal application. To inject, the toothpicks are withdrawn and the mix head nozzle is inserted into the tip. Conical shaped golf tees work better than standard tees (because of their thicker shaft) but are hard to find.

     Surface ports  plastic-injection-surface-ports-for-crack-injection

Injection molded of PE plastic or nylon, surface ports for crack injection have become very popular in the last 10 years. These consist of a flat base flange perpendicular to a small diameter tube for easy connection to the injection equipment using a 1/8” NPT press-to-fit connection. Although more costly from a disposable parts cost standpoint, field technicians appreciate the benefit of not having to manually hold the injection head against the port, particularly on ceilings or when time on port will be high.

     Packers, Zerk fittings and grease fittings

These port options for epoxy injection are popular when high pressures are used and are standards for use with chemical grouting, a term usually affiliated with polyurethane (PU) injection. PU is a material option for waterproofing and leakproofing but is not considered for structural repairs. Almost always these types of port connections are a most expensive cost option and are used with a drilled hole (see below). These connectors are often self-sealing with a spring loaded ball so the field technician doesn’t have to worry about material leaking from an uncapped port.

     Drilled Injection Ports

Port connections for drilled holes can be made by the contractor at low cost by cutting sections from 1/4 or 3/8” polypropylene supply hose (same as used for the water supply line for an icemaker), purchased as pre-molded units or supplied as a tapered Semko® tip. This method is one of the first choices when injection flows are obstructed by the type of crack, surface obstructions, plugging, or  for accessing voids under a sound surface (such as a de-bonded topping slab). If the crack is narrow, a water-flushed core bit is far superior to an impact bit as it is less likely to pack the crack around the hole with drill fines (leading to more obstruction).


Tags: plastic crack injection ports, concrete crack repair epoxy, concrete restoration epoxy