Ask the Expert Question-and-Answer Archive

by Ron Joseph

April, 2003

Painting Concrete Basement Floor

Q.The former owners of our home painted their concrete basement floor with polyurethene. It is now yellowing. What do we need to do to repaint the surface. If we need to scruff off the remaining shine, can this be done with a hand sander and 180 grit paper, or do we need to rent a floor sander?

A. In my opinion there is nothing you can do to prevent the yellowing, since all oil-modified polyurethanes, such as the one on your basement floor, will tend to yellow. The best you can do is recoat, but if the polyurethane is of the same chemistry as the first coating, you can expect it also to yellow with time.

If the polyurethane coating is sound such as no lifting, blistering, or peeling , then I would say yes, a good scuff sanding with 180 grit sand paper should take the shine off and create a good clean surface for the new paint to adhere. If you do find any areas where the paint is peeling, then you must clean the concrete surface and scuff sand the surrounding painted area to prepare the area for the new paint. A hand sander will be sufficient, however it may be very tiresome depending on the size of the area you wish to paint. A floor sander can complete the task in a fraction of the time.

I suggest cleaning the floor with a good detergent before sanding to insure that when you begin the sanding process there isn’t any grease or oil on the surface that may just get re-deposited into the new sanded surface and cause problems with the new paint sticking to the floor.

After sanding be sure to remove any and all sanding dust created from the sanding process with a mild detergent and allow the surface to dry completely prior to applying any new paints. Again this will help to insure a good clean surface for the paint to adhere to.

Please be aware that all paints, coatings and solvents are chemicals and therefore you should always pay close attention to the proper handling procedures and be prepared to wear protective clothing, such as respirators, gloves, coveralls, etc. always be sure your work area is well ventilated. For further information on the health and safety requirements for the coatings and solvents you wish to use. we strongly advised you to contact your local coating supplier and obtain a copy of the Material Safety Data Sheet (MSDS). If possible, go the extra step and look for this information on the website of the product vendor.