Garage Floor Preparation – Cement Preparation for Epoxy, Paint, Coatings, & Polyurea
Garage floors, like all concrete surfaces, must be properly prepared before coatings can be applied. Proper preparation ensures years of adhesion between concrete and coating surface. On the other hand, poorly prepared surfaces eventually fail because of poor adhesion of floor coatings.
The key principle in cement preparation is coarseness–coatings adhere more reliably and durably to coarse surfaces. Of course, cement surfaces must also be clear of waxes, polishes, and oils.
If you have an unfinished garage floor in your home, and your home was built in the most recent few decades, it is likely that your garage floor was machine-trowelled. Machine-trowelling is a process by which a large circular disk (think of a big Frisbee, upside down) is spun over a recently poured concrete surface. Trowelling smoothes the surface of the concrete and forces the aggregate (sand and small stones) deeper into the concrete, revealing a smooth, uniform surface. Trowelling produces a higher-quality concrete finish–unfortunately, however, machine-trowelling produces a surface that is generally too smooth and shiny to reliably accept a floor coating.
Preparing a Trowelled Cement Floor
Thus, trowelled floors must be coarsened before they are coated. Concrete is coarsened in two ways. One way is by acid etching (usually by muriatic acid), and the other is by physical grinding. Acid etching is achieved by simply applying a liquid acid solution to the concrete. Acid reacts with concrete and corrodes the surface, thereby roughening it. Acid etching must be followed by a thorough cleaning.
The Acid Etching Dilemma
Acid etching is widely regarded by industry professionals as an inferior method of concrete preparation. There are a few problems with this method of preparation.
First, acid etching does not abrade concrete sufficiently. The corrosive effects of acid only offer a mild coarsening of the underlying concrete. Remember, the greater the abrasion, the greater the adhesion. Second, acid etching often leaves a residue of acidic slime–this slime is often worse than doing no preparation at all. Finally, acid etching introduces water into the concrete–and water is the enemy of nearly all coatings. Some coating companies try to dry the remaining water with fans. Keep in mind that concrete retains moisture long after it appears dry on the surface.
Sadly, acid etching is routinely offered to homeowners as a preparation method. The benefits of acid etching lie primarily in its low cost–acid etching leaves extra money in the pockets of contractors. Similarly, acid etching kits, usually in the form of a dry powder, are included in inexpensive “do it yourself” garage floor kits that one finds in home centers.
The Superior Garage Floor Preparation Method: Physical Grinding
Physical grinding is the far superior method of concrete preparation, but it is also the more expensive. Physical grinding is generally accomplished through the use of a walk-behind machine that has one or more rotating plates containing super-hard, diamond-faced grinding stones. Grinding machines are expensive, and so are the replaceable diamond grinding stones.
Despite the cost, physical grinding offers the greatest and most reliable abrasion of concrete surfaces. Physical grinding produces a coarser surface, and leaves no residue or moisture behind.
Garage and Storage Plus offers physical grinding as its primary method of concrete preparation. Proper preparation is one reason that Garage and Storage Plus installations are the most durable floors available.