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"Surface prep is the crtical step for concrete floor
paint or any concrete topping."
The most important factor in making concrete floor epoxy paint durable and longlasting is proper surface preparation. Poor surface prep will result in poor adhesion and ultimately the flaking and peeling away of the coating. It's not a difficult task but can be a bit time consuming depending on what kind of shape the floor is in.
The first step is cleaning the entire surface, removing any dirt, loose debris and stains. For this you can simply use detergent and water, scrubbing with a brush and rinsing thoroughly. Be sure to hand scrub along the walls. You can also use a concrete cleaner/degreaser found at most hardware and autoparts stores. Once you've cleaned the floor, concentrate on removing any stains or removing any concrete sealers that remain. When you think you've gotten out all stains, pour water on them and look for any water beading up on the surface. If you find any beading, do some more cleaning. If water won't penetrate, then the concrete floor epoxy paint won't adhere.
Before washing any chemicals down the driveway and into the storm sewers, check with a local government agency on how to dispose of the chemicals you're using. You don't want to pollute streams and retention ponds. You will find that many cleaners can be sucked up with a wet vac and dumped into the sanitary sewer(toilet) without any negative effects.
The next step is acid etching. This will actually strip away some of the cement from the surface, opening the pores, and giving the floor a sandpaper-like texture allowing for good adhesion of the concrete floor epoxy paint. You can dilute muriatic acid with 10 parts water and 1 part acid. Always pour acid into water, never water into acid. When using muriatic acid, protect yourself with rubber gloves, safety glasses, long pants and sleeves, and a respirator. Because muriatic acid is dangerous, for most homeowners I recommend using a prediluted etching solution found at most home improvement stores especially when working in poor ventilated areas such as basements. Read all safety instructions on the label and take proper precautions when working with acid.
Spray the acid solution around the floor, covering completely and agitate with a brush. (Wear rubber soled shoes when walking in etching solution and rubber boots, if using muriatic acid.) The acid should cause a fizzing which indicates that it's working. When fizzing stops after 15-20 minutes, rinse with water. Repeat this process once or twice until the surface feels like fine sandpaper. Be sure to rinse thoroughly a few times with a hose and pressure nozzle. Let the floor dry overnight. You can use fans to help speed the drying.
If there is no plastic vapor barrier between the concrete and the subgrade, you should apply a liquid water and salt blocker which prevents water moving up through the concrete from breaking the bond of the concrete floor epoxy paint. (Most garages do not have a plastic vapor barrier underneath and most basements do have it.)
Simply spray the blocker on the surface making sure it is completely covered but not puddled. Roll out any accidental puddles.
The next day, or when the surface is completely dry, repair any cracks, holes, or spalling with an epoxy crack filler found at hardware stores. Simply fill the cracks and holes with the crack filler and use a trowell to scrape it flush with the surface. After a few hours when this is dry you are ready to begin applying the first coat of concrete floor epoxy paint.
Another option for the serious do-it-yourselfer is to rent a shotblast machine. It's like a sandblaster but it shoots tiny metal beads at the floor and sucks them back up as you go. The dust and debris is collected by a vacuum that's hooked to the machine. It will completely strip the surface including any coatings that are already on it. A shotblaster creates a perfect profile for any topping or concrete floor epoxy paint and won't make your house or garage dusty like a floor grinder will. The problem is they are expensive to rent and hard to find in most areas.