Removing efflorescence deposits on masonry walls...
Efflorescence is a fancy name for white, crystalline deposits that can appear on masonry or concrete. These deposits occur when moisture within the masonry rises to the surface, carrying minerals with it. The moisture evaporates, leaving the minerals behind. This often occurs with new masonry work and usually stops when the masonry has thoroughly dried.
However, if there is a source of moisture pushing through the masonry such as a damp below-grade foundation, the efflorescence will continue building up. I've seen some basement walls that looked like the Carlsbad Caverns!! The efflorescence on this wall (graphic left) is so thick (the white areas) that it falls off the wall like dandruff... and is piled on the foundation ledge like snow!
Severe, persistent efflorescence is not harmful, just a visible symptom of excessive moisture in the cement. Excessive moisture is the cause of a myriad of problems in the home, from stinky moldy basements to insect problems.
Today, there are various cement and non-cement-based products that can be used to seal foundation walls from the inside to reduce or eliminate efflorescence. However, efflorescence must be removed first for these products to stick properly.
Mother Nature does a great job on outdoor masonry via acidic rain, as efflorescence is rarely seen outdoors... but it takes years for a cement surface to be neutralized "naturally". For indoor work, efflorescence can be removed with plain water and/or with TSP and a very stiff bristle brush. A phosphoric acid masonry cleaner is also acceptable for indoor use. As mentioned earlier, don't mix TSP and acid!
If you plan on coating or painting the surface, consider using a phosphoric acid masonry cleaner before resorting to using muriatic acid! Follow the dilution recommendations on the product label or at the manufacturer's website.
If you must use muriatic acid to remove efflorescence, follow these steps (be sure to follow the safety recommendations earlier in this article):
- Dampen the wall.
- Mix the acid with water. 1 part acid to 10 parts water (by volume) is typical, but dilutions as light as 1 part acid to 16 parts water work well, too. (1-16 is easier to measure... that's 1 cup acid to 1 gallon of water.) Read the label on the product you buy and follow the recommendations, if any. Remember... add the acid to the water, not water to acid!
- Brush or spray acid onto affected area. Do not use a metal sprayer. A plastic sprayer will work for a while, but will eventually be destroyed by the acid. Have a few extras nearby and throw away used sprayers when finished.
- Let the acid sit for no more than a few minutes, less if you can see the efflorescence lifting.
- Scrub off any remaining residue with a stiff brush while rinsing thoroughly with water. There are long handled masonry brushes ideal for this job. To neutralize any remaining acid, you can spray a neutralizing rinse of one (1) cup household ammonia to one (1) gallon of water.
This is a nasty, sloppy and potentially dangerous job, so understand what you are getting into before you start this one! And I do not recommend using muriatic acid indoors except in extreme circumstances and, hopefully, by experienced professionals who know how to deal with the dangerous fumes!
Etching masonry for paint and patching preparation
"Etching" is a process where a chemical is applied to a surface to degrade it slightly. Etching is used to make circuit boards, where a thin copper sheet is selectively dissolved away to form a path for electricity. In masonry work, etching is a way to chemically clean and prepare masonry for repair or painting.
Actually, the process of efflorescence removal discussed above also etches the masonry. Etching roughens the surface of the masonry, allowing better adhesion and absorption of both paints and patching materials.
Use the same procedure and cautions for etching as described above for efflorescence.
Removing mortar stains from masonry and/or ceramic tile
Muriatic acid can quickly remove mortar stains from masonry. Again, phosphoric acid masonry cleaner may be adequate if the staining is not too severe. As any tile professional will tell you, phosphoric acid is routinely used for removal of grout residue from ceramic tile and stone.
Leave the acid in contact with the masonry for a minimal amount of time, in some cases just ten or fifteen seconds! New stains will release almost instantly. Quickly hose off all acid and reapply only as necessary until staining disappears. When satisfied, rinse thoroughly and then use a neutralizing solution of one cup household ammonia to one gallon of water and then do a final thorough rinse with water.
How to safely dispose of muriatic acid or clean up muriatic acid spills...
My appreciation Bert Tisher for suggesting I add muriatic acid clean-up and disposal information in this article. It was a huge oversight! Again, an observant reader comes to my rescue!!
Muriatic acid should NEVER be poured down a storm drain, a sink or flushed down a toilet. It can cause extreme damage to pipes, dissolve solder and damage the biological balance of your septic system. Throwing away even a closed container of muriatic acid with the trash can be dangerous for trash handlers, their trucks and possibly cause unexpected chemical reactions in landfills.
Small quantities of spilled muriatic acid will not cause widespread environmental disaster, but it can cause severe damage to plants and animals that may come into contact with it. It's easy to neutralize a muriatic acid spill common household and/or garden chemicals.
Here are some suggestions...
1) Recycle it!
Many counties or cities have drop sites for recycling hazardous chemicals such as oil-based paints and other household chemicals. Most will also accept muriatic acid. Call your local recycling center for more info.
2) Neutralize it!
Earlier, I mentioned using lime (the type used on lawns and gardens) to neutralize acid spills. Spreading a generous quantity of lime (the powdered or crushed type used for lawn or gardens) or baking soda and adding water will cause a distinctive "fizz" as the lime reacts with the acid to produce a harmless salt, water and release carbon dioxide. I prefer garden lime over baking soda since it is less expensive, is sold in larger bags and most gardeners have some laying around!
You can also use lime to neutralize leftover muriatic acid. Get a large bucket. I prefer 5-gallon size dangerous since the chance of dangerous spattering is minimized in a large bucket. Put three of four cups of lime in the bottom and a gallon of water. Give it a stir with a long disposable wooden stirrer (an old 1x2 is fine). Slowly add the acid to the bucket keeping your face away while pouring (and wearing your respirator). Stir, adding more acid and more lime until all chemical "fizzing" has stopped. The fully neutralized acid can now be safely disposed down a sink or storm drain without fear of damage to your septic system or the environment.