Q: We have an unfinished concrete block room in our basement. We’d like to paint the walls and finish the room. But how do you clean and prepare concrete walls that have never seen a brush? Any special paint or brushes we should use? What about sealing small mortar cracks? — Tina, via e-mail
A: A “finished” basement usually refers to building out from the concrete walls with framing, insulation, sheetrock and perhaps some attractive paneling. If you want the room to be a living space and especially if you want it to be a bedroom, you should consider finishing it completely. But if you merely want to spruce the room up for utility and storage, painting will make it seem less dungeon-y.
Although some homeowners have used Hydra Seal coating by Endura-Seal for basement walls, the manufacturer doesn’t recommend it for concrete walls. Look for a paint that’s intended for concrete, like Sherwin Williams ProClassic Waterborne Interior Latex Enamel.
Before investing in paint for the job, check to see if there is too much moisture in the cement; moisture will keep the paint from adhering properly. Tape a two-foot square of plastic to the wall with duct tape and leave it for a day or two. If there is moisture or discoloration under the plastic, the cement should not be painted.
If it looks good, decide what texture you would like the walls to be. If the surface is very rough and you would like it smoother, use a masonry filler and trowel to fill in the gaps and grooves to your liking. Clean the surface with a detergent-based cleanser or power wash, making sure there is no lingering dust or loose material on the walls.
If the cement is very smooth you will need to help the paint adhere by etching the surface with an acid-based etching solution or vigorous brushing with a wire brush.
Now, some words of caution: Wear a mask and gloves while scraping and etching. Some etching products, such as muriatic acid, are dangerous to use and dispose of, and wire brushes can raise stuff into the air that you don’t want in your lungs. And when it’s time to paint, ventilate, ventilate, ventilate! An enclosed basement room and paint vapors can make you pretty sick.