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Concrete Floor Coatings: On Grade vs. Above Grade
There are a number of different factors to consider when selecting a floor coating system. Here, we compare and contrast two garage floor applications, one on grade, one above grade.
*Note: This information is not intended to supersede information found in the manufacturer’s technical data sheets, which should always be read and followed in the application of any of the below materials.***
To begin, for both applications, the concrete should be shot blasted to a similar profile of 80-100 grit sand paper (also known as ICRI CSP-3). Manufacturers require a shot blasted surface – acid etching or grinding will not suffice. These coatings require a clean, solid, dry substrate. Contaminates like oil stains should be removed prior to application.
The grade of your slab will then determine the type of coating system to use:
On Grade: Epoxy Coating topped with a Urethane.
Epoxies are less sensitive to moisture and have greater adhesion when compared to urethanes. A urethane top coat in this application prevents the epoxy from being damaged by UV light.
1) Begin with BASF High Build Primer mixed with the desired epoxy color, squeegee and roller applied. The High Build Primer's coverage is 100 SF / gallon.
2) Unimin 2095 Sand, broadcast at 12 lbs. per 100 SF, back-rolled into the High Build Primer. The use of sand adds to the wear ability as well as making this a better non-slip surface.
3) Sikafloor 340, squeegee and roller applied as a clear finish coat, should the floor require a UV-resistant coating. Coverage is 375 SF / gallon.
Above Grade: Urethane Coating.
Urethanes provide flexible waterproof layers where the threat of ground moisture isn’t present.
1) BASF Sonoguard Base Coat, squeegee and roller applied and allowed to dry. Coverage is 60 SF / gallon. The above grade coating provides a traffic bearing waterproofing system that will also protect the area below the slab.
2a) BASF Sonoguard Top Coat, squeegee and roller applied with Unimin 2095 Sand back rolled into it. Coverage for the Top Coat is 80 SF / gallon. BASF Sonoguard Top Coat is stocked by BW in Gray, but is also available as special order in charcoal or tan.
2b) BASF Sonoguard Tint Base Top Coat may be used for surfaces intended for PEDESTRIAN TRAFFIC ONLY. Coverage is 80 SF / gallon. This product allows for colors with the addition of NP-2 Color Packs. Squeegee and roller applied with Unimin 2095 Sand back rolled into it.
When Should Floor Coatings Be Avoided?
The presence of moisture should be the major factor when considering a floor coating. Epoxies and Urethanes are not breathable coatings. Excessive water vapor drives up through slab on-grade surfaces which have an epoxy and/or urethane coating, and is not allowed to escape. This trapped vapor drive has the potential to cause surface damage to a slab’s surface by way of “pop-outs”. Unless it is known that there is a vapor barrier underneath a concrete slab on-grade, it is always best to do a surface moisture test on the slab before proceeding.
Floor Coating Accessories for the Job