Removing garage floor paint is the recommended option if the paint is old, chipping, and flaking. In these cases, the old paint is too damaged to be used as a base coat for a new coat. There are several options of stripping off your garage floor paint, and some are simpler and less hazardous than others.
Step 1 - Remove Stains
Use a strong detergent to wash away any garage floor stains caused by oil, gasoline, grease, or the like. Scrub stubborn ones with a sponge or cleaning brush until completely removed, and then be sure to rinse thoroughly. Do this with a rented pressure washer if you can obtain one. If not, use the high-pressure nozzle setting on your garden hose.
Step 2 - Apply Deglosser
Garage floors are often painted with coats of high-gloss paint because of its durability. This can also make it more challenging to remove. Chemical deglossers are available in your local hardware store's paint department. Be sure to follow all instructions for using these to remove the top gloss coating of the floor paint, and always work with these types of chemicals in a well-ventilated area. Keep your garage door open, and also open any side windows during this process.
Step 3 - Apply Paint Stripper
Strong paint stripping agents can be used with either a blast machine or applied by hand using a stiff wire brush to loosen the rest of the garage floor paint. If you apply paint stripper with an abrasive blast machine, you have much less exposure to this strong chemical that can potentially cause respiratory problems if too much of it is inhaled in too high concentrations. Check with your local paint supplier about renting one of these blast machines in addition to a pressure washer.
With either paint removing option, it is strongly advised to wear protective painters' clothing and a face mask to keep from breathing in paint stripper fumes. If a traditional paint stripper proves to be ineffective, your garage floor could be painted with an acrylic-based paint, in which case you will need to apply a stronger remover known as muriatic acid; the same precautions apply.
Step 4 - Buff and Clean
A final optional measure to completely remove stubborn acrylic garage floor paint if the above steps fail is to use a floor buffer. This can also be rented from a hardware retailer, along with abrasive pads for maximum paint removal. Keep the garage floor wet one area at a time to keep the pads from becoming too worn down from the concrete under the paint.
Thoroughly clean off from your garage floor any remaining chemical residue from paint strippers and/or muriatic acid. Use another application of detergent, followed by a rinse from your pressure washer or garden hose nozzle. Allow the entire floor to dry for at least 24 hours before starting to apply a new coat of paint or before moving your vehicle back into the garage.