Changing the Mortar Color on the Fireplace

Rock fireplace with dark mortar in living room

Changing the color of the mortar on your fireplace can give the whole room a new feel.

Mortar is the “grout” in your rock fireplace. The term grout is more commonly used when referring to ceramic tile installations. Grout fills joints between tiles, and mortar joins stone together.

In addition to providing a solid bond between the stone, it can also add to the design and interest of stone or brick.

In any case, you can change the color of the mortar a couple of ways.

Muriatic Acid

If the mortar is just a touch too dark and you want to lighten it up a wee bit then start with a 10-percent solution of muriatic acid. Apply the solution to the mortar joints only using a small bristle brush or similar device. A little of this mild acid on the stone or brick will generally not hurt so long as you don’t allow it to remain for very long.

Allow the acid to remain on the mortar joints for at least five minutes or until it has stopped fizzing. Rinse the area completely and allow it to dry. You may need to wait a few days until it has dried completely to determine if the process worked. If the mortar has lightened but the desired result has not been achieved, give it another acid treatment and allow it to dry to check the results.

Remember, safety first. Wear rubber gloves and eye protection. Make sure there is plenty of ventilation in the area when working with acid.

Apply a New Mortar Layer

Another way to change the color is to remove about a 1/4″ layer from the surface of the existing mortar using a hammer and chisel and apply a new layer in its place. Mix powdered pigment in with the new mortar to create a color to suit your decorating needs.

First, make a few test samples on a board to make sure that you have the desired color. Be sure to allow the sample to completely dry since mortar will typically lighten as it dries.

Further Reading


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