What You Should Know Before Applying a Garage Floor Coating

If you are planning on resurfacing your garage floor with an epoxy or polyaspartic coating there are a few things to know to prevent problems later.

Moisture In Concrete

Concrete is mixed with water which is an obvious statement, but what happens during the cure process? Water combined with ash, sand, aggregate and water creates a chemical reaction that turns the mix into a hard substance. The cure cycle called hydration is part of the chemical process. Excess moisture will work it's way to the surface leaving a trail behind it. As the moisture goes to the surface the concrete hardens and the trail left behind the water is an air hole or vein. Moisture pressure will push upwards traveling to the surface through these pores.

There are two types of pressure that can cause a coating to have problems. There is capillary and hydrostatic pressure. Hydrostatic pressure happens when concrete is below grade. Moisture below grade creates tremendous pressure that pushes upwards through the tiny air holes in concrete. As it pushes upwards it pushes salts to the surface as well. Capillary pressure has a similar result with less pressure. Either way the moisture and salts can cause coatings to chip and delaminate.

Checking For Moisture In Your Slab

The easiest way is to tape plastic down to the floor in a few areas. You can also put down heavy rubber mats on the floor. If after 24-48 hours you have condensation underneath you have a moisture issue. It is possible to get different reading at various times of the year. In colder climates you will have minimal moisture in winter or early spring that can increase when the ground thaws. If your concrete is above grade with a basement below you will likely have little if any moisture.

Choosing a Coating

There are epoxies and polyaspartics or polyureas products for coating a garage floor. Whatever you choose surface prep is the most important first step. Cracks should be filled with a polyurea filler for best results. Polyureas can be thin enough to completely fill a crack to the bottom. Your concrete is likely about 4 inches thick. A crack will go all the way through. Filling the crack to the bottom with a filler that will cure below grade, absorb into the walls of the crack and flex will keep moisture vapor from traveling to the surface. There are also some heavy duty epoxies used for waterproofing that are an excellent alternative.

The next step is to etch, shotblast or grind the surface to either provide increased surface area or open the pores of the concrete. Etching with a gel acid is a simple and effective way to profile the concrete with results similar to shotblasting. Shotblasting is the process of shooting thousands of tiny ball bearings at the surface. Either process will abrade the surface feeling like 100 grit sandpaper. This is the process before applying an epoxy coating.

Floor grinding is another surface prep method which opens the air holes and veins of the concrete while also removing the highs and lows of the floor. This is the correct process if using a polyurea or polyaspartic coating. These two materials are different than epoxies. Polyureas absorb into the airholes and veins in concrete and actually cap off the surface preventing moisture damage. Epoxies do not have the capability to absorb into concrete. Instead they stick to the surface. The process of etching or shotblasting substantially increases the surface area for epoxy to stick to.

If you have low traffic and no moisture you may be able to get away with an epoxy paint. In a garage a high performance epoxy or polyurea is the best choice for holding up to hot tires caused by road friction and chemicals that may drop to the floor. If moisture is an issue a properly prepared floor with a polyurea coating is your best choice.

Another difference to consider between an epoxy and polyureas is what happens with micro scratches that are inevitable. Epoxies get a frayed edge from scratches which trap dirt and surface moisture creating a bacteria build. Surface scratches on a polyurea are straight making it easy to clean and avoid bacteria build.

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