How to Remove Mortar Stains and Smears

Remove mortar stains from brick, block and concrete

Mortar stains and smears make the surface of a masonry structure ugly. Mortar stains and smears often remain after new construction or can be the result of aging.  Over time bricks and blocks may become stained due to “efflorescence.” Efflorescence is the result of salt and other mineral deposits seeping out of the mortar. The efflorescence stain can be removed by using a few basic techniques used by professional masons. Over the past 20 years I have used these techniques many times to remove unsightly mortar stains and smears from brick, block and concrete.

Things You Need for the Project

Rubber Gloves and Safety Glasses

Power Washer

Bucket

Water

Muriatic acid

Garden Hose with spray nozzle

Stiff-bristled brush

Extension pole

Steps

1) Spray the surface with the power washer. Use the power washer to remove as much excess mortar debris and stains as possible.

2) Put on the safety glasses and rubber gloves. Muriatic acid can cause burns, so you want to wear safety gear at all times for protection.

3) Pour approximately one gallon of water into the bucket. Slowly add about 1 ½ oz. of muriatic acid to the water. Be careful not to splash the acid. You want to use a cleaning solution of approximately one-part-acid to ten-parts-water to begin the cleaning process. This ratio should be effective to remove most mortar stains. Gradually increase the strength of the cleaning solution, if necessary to remove tougher stains.

4) Spray the masonry surface with the garden hose. The surface must be wet before you begin to use the acid wash cleaning solution.

5) Put the stiff-bristled brush on the extension pole.

6) Place the brush into the bucket to saturate the brush with the cleaning solution.

7) Apply the cleaning solution to the masonry surface. Use the brush to scrub the mortar stains and smears off the brick, block or concrete surface. Repeat this process until all the mortar smears and stain are gone.

8) Spray the surface with the garden hose to remove the acid residue. Use plenty of water to make sure that the surface is completely free of any acid residue.

Warning

Do not powerwash or use an acid cleaning solution on a newly constructed masonry structure. New mortar must be allowed time to properly cure. Generally, a period of about 30 days is needed.