Concrete methods to deal with the fungus among us
By Ven Griva
Copley News Service
For years now interlocking brick retaining walls and raised flower beds have been all the vogue. If you have installed such a system in your landscaping, you might have noticed that time and Mother Nature have conspired to tarnish them.
If green or black wasn't the color you were shooting for on your patio, walkway or walls then you might have a problem with fungus, moss or mildew. There are a couple of solutions you might consider to return your blocks to their original chocolate, tan or gray.
First, you can use water, elbow grease and a stiff, nonmetallic bristle brush. It is the method that is safest for the environment, though it might be hard on your back.
Another method is to mix 1 quart of household liquid bleach into 1 gallon of warm water. Apply with a stiff bristle brush and then rinse the solution off liberally with clean water.
The active ingredient in bleach, sodium hypochlorite, might not dissolve large masses of these types of growths. If not, scrape off as much of the growth as possible with a putty knife or wire brush; then, scrub on the bleach mixture.
When trying to eliminate fungus or mildew, it's the bleach that does the job, not elbow grease. Make sure you give the bleach plenty of time to work before scrubbing and rinsing away. If not, fungus or mildew spores will remain and can spring quickly back to life.
Another problem with masonry retaining walls is efflorescence. That's the white, fuzzy stuff that appears to sprout from brick, masonry and concrete. It is caused by salts that are in the brick and mortar or are transferred into the masonry by water.
These salts can even be in the dirt used to backfill these walls. When the water evaporates, the salt comes to the surface and dries there.
Sometimes, efflorescence will stop on its own. It can cease if the supply of soluble salts in the bricks or mortar becomes exhausted. It can also stop if the source of water that dissolves the salts is cut off. And the process can stop if the water that dissolves the salts is prevented from getting to the surface of the masonry.
Unfortunately, retaining walls or masonry walkways located in gardens or flower beds will probably always be subject to water through irrigation. Consequently, if the back or top of the wall was not treated with a compound that will prevent water penetration, it could take years for efflorescence to disappear.
Depending upon the soluble salt or salts that are causing the problem, you have several options for removal:
- You can remove the dried deposits with a stiff brush.
- You can use water to wash the salts from the wall. However, this process can sometimes dissolve the salts and cause them to soak back into the wall.
- Finally, you can use a very weak solution of muriatic acid. Only attempt this method if you know for a fact that the acid will work effectively on the type of salt present. Generally, the formula is 12 parts water to 1 part commercially available muriatic acid.
Acid-resistant gloves, splash goggles and other protective clothing should be worn when using any chemical solution. Precautions on label should be observed because many chemicals can affect the eyes, skin and breathing.
For integrally colored concrete masonry units or mortar, a more dilute solution, 15 parts water to 1 part acid, might be necessary to prevent surface etching that could reveal the rock and sand in the concrete aggregate and change colors and textures.
Before using any chemical to clean masonry, it should be tested in a small, inconspicuous area to be certain that there will be no adverse effect. When using chemical cleaning compounds, it is wise to flood the surface with clean water to prevent the chemical from being absorbed deeply in the masonry and causing damage.
Application should be to a small area, not more than 3 or 4 square feet at a time. Wait about five minutes before scouring off the salt with a stiff non-metallic brush.
Immediately flush with clean water to remove all acid. Since an acid treatment might slightly change the appearance of treated areas, it is generally best to wash the entire wall or flower bed to avoid discoloration or mottling.
Solutions to solving efflorescence problems should focus on eliminating the source of moisture into the structure. One way to achieve this is to install a drain at the bottom of your retaining wall or raised flower bed. This will direct water away from the wall and speed up the drying process.
Using a masonry drill bit, drill pilot holes through the masonry joints at the base of the wall to release water. Enlarge the holes and insert drainage tubes into joints. Caulk around the drainage spouts with cement caulk.
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