1.) Concrete Prepping Methods Used to Apply Concrete Coatings
There are 3 basic methods that a professional concrete coatings contractor or DIY homeowner can use to prepare the concrete surface for applying concrete coatings like epoxy, polyaspartic or polyurea.
The first method is a chemical etching process where muriatic acid is applied to floor surface with a garden sprayer and let sit for 5 to 10 minutes to give it time to react with the concrete. It should be neutralized with ammonia to balance the pH and then rinsed with sufficient amount of water from a hose or surface cleaner. Most DIY concrete coatings recommend this method because it does not require expensive equipment or significant training. However, it is not the preferred method of professional contractors as the surface is only marginally prepped for the coating, causing premature failure often in 1-3 years. There are newer water-chasing epoxy primers or polyurea primers that may fit this application better and give similar results to grinding or shot blasting.
The second method of concrete prep is by diamond grinding. Most floor coating contractors will own their own equipment, but homeowners can also rent them. The diamonds are an extra charge and should be matched to the hardness of the concrete slab by using a MOH scale test. MOH scale testing is a scratch test using a scale from 0 to 9. A "hard concrete" diamond tool will be applicable to a MOH scratch test of 5 to 7. Grinding soft concrete with a diamond meant for hard concrete will cause significant tool wear. Grinding can be done with 40-80 grit diamonds in most cases. Diamonds are best used for removing paint or leveling an uneven or rough concrete surface. PCD segments can be used on the grinder to remove more difficult or thicker coatings like epoxy or paint. Diamond grinding with a larger machine will identify dips or low spots in the floor where the grinder skips that area or high spots where more grinding occurs and exposes aggregate in the concrete.
The third method of concrete prep is with a shot blaster. Shot blasters shoot steel balls at the concrete surface and profile the surface. This may be a preferred method preparing for epoxy or polyurea which are typically applied at 10-25 mils thick. If there is a low spot, the shot blaster will profile it the same as the high spots, thereby not leveling the surface as well as the grinding process would. Having a low spot like in a garage floor will allow water to puddle, which could have an adverse affect on the coating over time.