Manuals Can’t Account for Everything
In all honesty, a company will probably spend more on prepping a concrete surface for repair, than on the epoxy coating itself. I recall the first project I managed in North Carolina – it was for an expansion of Palmer Wahl in Asheville. The company manufactures thermal imaging devices. The plant they were moving into was originally a textile facility, with row after row of machinery that had long since been removed. The challenge we faced was that a rubbery material, most likely installed in the 1960s as cushioning for machine operators, had now become one with the concrete. The instructions for the industrial floor coating we were using told us the surface had to be cleaned and prepped, but we were left to our own devices to figure out how to remove the rubber flooring that had become fused to the concrete. After calling everyone we knew, we finally found a citrus-based solvent that dissolved the rubber.
Technical manuals will go on and on about how important surface preparation is, but since they are not looking at your existing slab, they can only give you generic information on how the surface should be cleaned, prepped, cured, etc.
Remove Surface Contamination
Bottom line, any defects in the concrete being repaired can cause the bond between the original concrete and the new epoxy coating to fail, so you will need to spend some time preparing each surface for application. It is often a good idea to remove any surface contamination by “shot blasting” the concrete. In the old days we called this sand blasting. This work has to be performed by properly-trained crews as the dust is not healthy. Be prepared to have the work area evacuated during this process. The crews must wear proper protection to avoid breathing in any of the fine dust. The process can be engineered to remove surface contamination and create a proper texture, depending on the gauge of sand that is used.
Rough Polished Areas
Epoxies do a great job of bonding, but increasing the surface area by making it “rough” gives an even stronger bond. Most used slab surfaces become polished over time as traffic crosses the surface. The older the slab, the more the top layer of concrete tends to become sealed with finely ground and polished debris. Polished concrete will appear shiny. Shiny is not good. The new polymer epoxy coating is going to have specified bond characteristics, and, in theory, is designed with a stronger bond than the strength of the existing concrete. The fine print on epoxy products will always say that the existing surface has to be “properly prepared” prior to application. What that means in real life, is that if the new epoxy merely floats on the surface of the concrete and bonds with the years of polished debris, rather than penetrating the substrate itself, you concrete repair will fail! Entire sections of brand new epoxy coatings have been known to shatter with use because the surface was not prepped and the epoxy polymer did not achieve an optimal bond with the substrate.
The preparation of the concrete being repaired can have as much to do with the bond strength as the specification of the new product being applied. Having a properly prepared and cleaned concrete surface allows the applied epoxy coating to wick into the old material, say the first 1/16 of an inch or more, creating a deep bond. If you were to cut out a piece of the slab after the epoxy is cured, you would see just how deeply the polymer has fused into the old material.
Penetrate Old Sealants
One thing to keep in mind is that many concrete slabs were sealed at some time. The sealant may not be obvious, but if it is there, it needs to be removed or “activated”
For concrete repairs in wet or corrosive environments, new polymers have been developed to increase wear life such as those with Novolac technology. These Eco-Polymers overcome some of the drawbacks of legacy engineered epoxy coatings. Take a look at the specifications for Eco-Polymer epoxy coating products, for instance: http://www.csscorp.net/
Check for Curing
Another thing to carefully check is the status of the existing surface’s cure. Concrete will continue to cure to some extent over its lifetime. I recall a 40 year old slab we were struggling to attach fasteners to. When new, the lab tested at 4000psi. After conducting our test 40 years later, the concrete had cured to 7000psi. No wonder we had trouble attaching the fasteners! The reason this is important for applying epoxy coatings is that the material may still be undergoing the curing process. This is not evident to the eye, and careful moisture testing is essential before proceeding with adding a new polymer surface. If there is an unfinished, ongoing chemical reaction in the concrete, this can interfere with the bonding designed for the new epoxy coating. Next generation primers overcome some of the limitations of older type primers that sometimes interacted with the existing concrete.
A great example is Construction System Supply’s Eco-Polymer Concrete Primer/Sealer SC-1100 that can be applied to green concrete as young as seven days, helping eliminate outgassing and bubbles. Designed to seal concrete, this 100% solids low-viscosity Novolac primer strikes deep into the concrete. It mixes easily with sand to form a very strong repair material. For more information visit the product page: http://www.csscorp.net/
About the Author: James Titus is a General Contractor in North Carolina with over 30 years of commercial experience. Mr. Titus has completed over 400 commercial projects ranging from high rise renovation to new construction.
James Titus wrote this informational press release on behalf of Construction Systems Supply, national industrial supplier of top-quality epoxy coatings and concrete protection and repair products. For more information about industrial epoxy coatings, visit www.csscorp.net