Power Washing and Roof Cleaning Forum

Efflorescence evolves into various forms and because of this, there isn't always one easy solution to remove it. In this post, I'll talk about how efflorescence occurs and some cleaning strategies. As a manufacturer, we provide cleaners for hard to remove efflorescence issues but often times there are easier ways to go about cleaning the "salts" from the surface and I encourage any readers to discuss their own solutions in this blog.

WHAT IS EFFLORESCENCE & WHY DOES IT OCCUR?

Efflorescence in its most general form is comprised of water-soluble salts that migrate to the surface of the masonry (or concrete) via water or vapor transmission. Water is always the active agent that brings efflorescence to the surface. You tend to see it worse on retainer walls because there is ground source water on one side "pushing" the water/vapor to the opposite "exposed" side of the wall, as well as, rain falling on the exposed wall that will help "draw" the salts to the surface. Efflorescence most often looks like a powdery white deposit but it can also look grey, black and even green depending on the region of the country and type of salt composition.

Water carries the dissolved salts to the surface and as it evaporates, it leaves behind the crystalized deposits. In this "early stage" of efflorescence development, it's usually pretty easy to just brush away the salts or use a weak, water-based solution to dissolve them. Yet these early stage deposits are only water soluble for a brief period before the carbon dioxide in the air converts the deposits into water insoluble (calcium) carbonates that harden. Over time these carbonates can grow like a stalactite and the pores will close up. At this point, even a strong acid cleaner can just bounce off the surface. 

REMOVING EFFLORESCENCE

As previously mentioned, in its earliest form the salts can be easily removed. Once the carbonates have formed, it often requires a combination of mechanical and chemical effort. That means using a stiff bristle brush to "open up" the pores and mechanically trying to knock away as much buildup as possible before going chemical. Yes, labor costs should be adjusted higher for these scenarios. A muriatic acid wash is often used, but you should take care as too strong a solution can burn the brick/concrete and too weak a solution will bring the pH up too high to have any effect. Whichever cleaner you try, if using a power washer to rinse be sure to hold it at an angle to the wall. Direct injection of water can cause additional efflorescence to be drawn to the surface. 

BELOW ARE SOME EFFLORESCENCE SCENARIOS THAT WE'VE ENCOUNTERED:

Jefferson Memorial, Washington DC 

This project for the National Park Service entailed removing efflorescence from 17,000 square feet of new colored aggregate concrete. As the concrete cured it began drawing the salts to the surface and became very noticeable against the dark grey surface. Because the concrete was so new (tender) we decided to use our EnviroEtch which although is a 1 pH acid, it is more buffered and not acidic to human touch.

Tiled Stairs

In this case, the efflorescence was bleeding out of the mortar joints. Mortar joints are often subject to this problem because the sand used to make the mortar can be contaminated with soluble alkali sulfates which leach to the surface.