Coatings for Concrete
Concrete is our most common building material. While this versatile material seemingly lasts forever, it nevertheless is subject to degradation from water, pollutants, chemicals and even microbes. As an example, heaving and spalled concrete is a common sight resulting from freeze-thaw cycles and bombardment from deicers in harsh winter climates.
GemThane has had a long history of maintaining concrete. Our polyurethane and epoxy coatings have been used in applications including: storage tanks containing everything from potable water to industrial chemicals, industrial floors, wastewater treatment facilities, manholes, lift stations and even marine aquaria.
A Note About Surface Preparation
We mentioned earlier that concrete is a relatively porous and non-uniform material. As a result, surface preparation is critical. Most commonly, a light abrasive blast is used to remove chemicals used in the casting process and byproducts such as laitance and efflorescence. It cleans-out bugholes and leaves an angular surface profile. Alternatively, the surface can be treated with GemBond Surface Conditioner, a soap-like foam that will etch the concrete, open the pores and remove contamination. Apply with a simple sprayer, leave for 15 to 30 minutes and power wash off the residue with hot tap water.
The surface is now ready for coating. For many applications, particularly those that involve immersion or even intermittent fluid contact, a seal coat is recommended before the main coating. This alleviates a common phenomenon with concrete called off-gassing, which may cause blister formation and other defects in the coating. GemThane has two products that help prevent this problem, namely MG-201 and MG-220. These are easy to use Mix-and-Apply 100% solids modified epoxy-polyurethane hybrid coatings that flow into the profile, seal micro cracks and pores and provide an anchor for a variety of Madison topcoats. MG-220 is more bodied than MG-201 and is the preferred choice where higher build and resistance to slumping on vertical surfaces is required. Within four to six hours they are ready to accept topcoats, and can be topcoated up to 48 hours later. We encourage you to contact us if you have any questions about surface preparation.
For the purposes of the following discussion, we will assume that surfaces have initially been sealed with either MG-201 or MG-220.
For atmospheric service, two primary topcoats are used, depending on the industry and the anticipated service conditions.
In many moderate service applications, a single coat of GemThane OverCote aliphatic polyurethane with either MG-201 or MG-220 basecoat will provide the desired service life. If maximum UV stability is a priority, finish with GemThane 1:4 Aliphatic topcoat (contains aircraft grade resins).
Embedded and Immersion Service
For embedded and immersion service, there are a couple of options. GemThane Liquid Rubber is a self-curing, paint-like liquid with high resin content (low solvent). The product cures to an elastomeric, rubber-like film that exhibits superior elongation, flexibility and impact resistance. Liquid Rubber will cure down to as low as 15ºF (-10ºC). GemThane “S” is a single-component-plus-catalyst aromatic polyurethane coating that is very resistant to chemicals, abrasion and immersion conditions. Both of these products are designed to be used over either MG-201 or MG-220 basecoat.