Ask the Expert Question-and-Answer Archive

by Ron Joseph

February, 2002

Painting Concrete that has "Efflorescence"

Q. My question is which type of paint do I use (oil,latex, primer? etc) when painting over a concrete block basement wall that has had "effervescense" on it? (that white stuff that grows on it). Would it do to simply scrub the wall with TSP or another product and then paint? Or should I just paint with some suitable product? HELP!!!

A. If the "white stuff" that you referred to is in fact "efflorescence" then in many cases it is due to soluble salts that are excreted from the cement. The salts are often alkaline. Since trisodiumphosphate is higly alkaline, it might not be the best soltion to your problem. You might be better for you to brush off the "white stuff" with a stiff bristle brush and then follow by thoroughly washing the walls with clean tap water. Allow the walls to dry out to allow for any additional "white stuff" to come to the surface, which you then remove. Also, please go here for the names of commercial compounds that you can use.

Make sure the white stuff is white and not green or mustard colored which indicates mold or mildew. In that case, wash the mold/mildew with 1-part laundry bleach, 4 parts warm water. Brush into affected areas and rinse with top water.

There are many types of latex coatings on the market that include primers, sealers, block fillers and finish coats; all intended for masonry surfaces.

Apply one coat of masonry sealer followed with one or two coats of acrylic latex masonry topcoat, either semi gloss or flat.