A Landscaper's View

After the flagstone walkway is completed and the mortar has set, it is necessary to wash the stone of its concrete residue and “drippings.”  It’s most common to acid wash the walkway or patio.

Concrete residue

Here is an excellent set of instructions that I came across for acid washing a walkway or patio, especially since our crew uses Type “S” mortar mixed with sand for our mortar mixture.

Type “S” (and Type “M”) mortar is very difficult to remove from the face of all brick, but is a special problem when through-the-body or light colored brick is used due to the sensitivity of these brick to strong cleaning materials.

The following cleaning procedures are recommended according to age of masonry work:

A. After work is 10 days old:

1. Remove all large mortar particles with hand tools before applying cleaning solutions.
2. Mask and otherwise protect adjacent non-masonry materials.
3. Saturate wall with clean water.
4. Use cleaning brush to apply solution of Sure Klean Vanatrol, Diedrich 202 Vana-Stop (or equal) mixed 4 to 6 parts of water to 1 part of solution.
5. Allow solution to remain on wall for 3 to 5 minutes while brushing and scraping, reapply solution.
6. Thoroughly rinse and brush clean.

B. After work is 30 days old:

1. Use procedure described above in steps 1-5.
2. Use high water pressure equipment to rinse wall, using pressure not greater than 800 PSI with a 40 degree nozzle fan tip. Consult brick manufacturer before using high pressure water system.

(Test clean a sample area to determine effectiveness of cleaning compound and the total cleaning system and to check wall for possible damages caused by system. Approval of owner or owner’s representative should be obtained before proceeding with operation.)

Per the first step, it is necessary to remove larger chunks with a trowel or other hand tool.

After we removed the larger chunks, we took a wire brush to scrap off the light concrete residue.  It does not take much effort, and the light residue rubs off as a dusty powder.

The last step is to pour the acid on the stone and mortar, let it sit, and brush it into the walkway or patio stone before washing it off with clean water.

There are a number of acid products out there, however, it is highly recommended not to use muriatic acid on your project.  Muriatic acid needs to be diluted A LOT, and even then, is a very powerful substance.  It will kill plants and eat your blue jeans. Take this warning to heart before using muriatic acid.

Muriatic acid is just that, acid. It has no wetting agents or detergents to help control the acid and keep it on the surface of brick where it needs to be. Muriatic acid can cause bleaching and streaking of the masonry face, etching and removal of the mortar paste from the mortar joints, and cause a yellowish acid burn discoloration. If muriatic is used on brick that contains vanadium, iron, or manganese it will cause activation of these mineral salts resulting in yellow, green or black staining developing on the face of the brick. This is why brick manufacturer’s say “ do not use muriatic acid” to clean new masonry construction. Rather, they want proprietary blended hydrochloric acid detergents used. Additionally, muriatic acid will not clean old dirty brick. It is unable to break down and remove atmospheric carbon and pollution from masonry surfaces.

Instead of muriatic acid, a more mild detergent should be used, such as Diedrich 202.  Be sure to follow the directions on the side of the bottle or consult a professional for proper use.

After the acid wash is complete, be sure to wash off your patio or walkway with running water.

Final rinsing