The white alkaline substance that often crops up on cinder block walls is called efflorescence. Efflorescence has two primary causes. Water on the surface of the bricks may leave mineral deposits behind as it evaporates. Or, water on the other side of the wall may move through the cinder blocks and deposit minerals from inside the cinder blocks onto the surface. Efflorescence is easy to get rid of with a little cleaning. However, you must find the source of the water and eliminate it or the efflorescence will crop up again.
Things You'll Need
Solvent reistant gloves
Solvent resistant scrub brush
Mix a soap solution of 1 tbsp. liquid detergent soap per gallon of water.
Brush the bulk of the deposits off of the surface of the wall with a dry brush. If the white stuff flakes off, the deposits are on the surface of the wall. If the white stuff doesn't budge, the efflorescence came through the interior of the brick and it's behind the sealant. In this case, move on to Step 5.
Dip the scrub brush in the soap solution and scrub the white areas. Rinse frequently. Keep scrubbing until you make no more progress. Then rinse the wall clean.
Allow the wall to air dry and inspect it. The soap and water may be enough to remove the efflorescence. If some is left behind, scrub again. If that still does not remove the white stuff, there may also be efflorescence underneath the sealant. Move on to Step 5.
Wet the white portions of the wall (and roughly one foot beyond) thoroughly.
Mix the muriatic acid with water in a plastic bucket according to the container's instructions (usually 5 parts acid to 100 parts water). Always pour acid into water, never water into acid.
Mix 1 part ammonia and 1 part water in a separate bucket. Keep it on hand near the treatment area.
Apply the solution to the wall with a rag. Avoid drips as much as possible. Keep a bucket of clean water and a sponge nearby and clean any spills immediately. Scrub the walls with a scrub brush. Scrub slowly and carefully to prevent the solution from flicking off the walls and onto you or the floor.
Leave the muriatic acid solution in place for five minutes.
Rinse the wall with the ammonia solution to neutralize the acid. Use as little solution as possible to avoid drips. Use a dedicated sponge for the ammonia wipe. Don't transfer the acid sponge to the ammonia.
Rinse the wall with clean water and a sponge. Use as little water as possible to avoid drips. Rinse the sponge frequently as you wipe the wall down. Rinse a second time to make sure all of the acid is gone.
Allow the cinder block wall to air dry, then observe the wall. If there are still white deposits left on the wall, repeat Steps 8 through 11 until they are gone. Rinse three times after the final application to make sure all of the muriatic acid is gone. Any residual acid can slowly erode the cinder block.
Wear a dust mask when using acid and scrubbing efflorescence.
Wear long clothing, protective gear, hair covering and closed toe shoes when handling muriatic acid. It is one of the most dangerous chemicals available for home use.