Do you have a damp brick or concrete wall? Beware of quick fixes
Whenever and wherever damp conditions exist, mold is sure to follow. And, although brick and cement block are sturdy building materials, they have a weakness–they are very porous to water. This means that unless you have a way of drying those beautiful brick walls to one side or the other, retained water will allow mold to form on them or near them. Europe has been battling “damp and mould” for ages because most residences are built with cement block or brick structure, as opposed to wood structure in the US (which has its own challenges). However, basements in the US are usually formed with cement block or poured concrete walls, which have the same problems.
Here’s the thing: you can have your brick or cement AND a comfortable, low-mold living space too. (We say low-mold because mold spores are ever-present in the air, we just don’t want to give them food and water to establish themselves). How do you co-exist comfortably with brick or cement walls? By providing a way for that water that penetrates them, to exit (dry). First, we’ll look at two ways water gets into brick:
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Direct contact with rain, landscaping sprinklers or leaks: Brick and cement are porous, meaning they have tiny holes that allow water to come in. We have a whole article on why brick alone does not make a waterproof siding, meaning it can’t keep the rain out. (And sprinklers hitting a wall of your home is always a bad idea!) If you have brick siding on your home, or stuccoed cement walls with no waterproofing, then you’ll want to keep the rain off it as much as possible with large overhangs, working gutters, and a gap between it and the interior wall, so that water that gets through is not directly transferred to the interior wall.
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Water vapor: Water vapor is carried in the air, and some older homes were typically built with no or little “barrier” or retarder to keep the air and water vapor out. Since brick and cement are porous, water vapor can diffuse through them and give that “damp” feeling inside.
Building the Perfect Wall by building science expert Joe Lstiburek explains that if you have brick veneer, you need a “drained cavity” right behind it. This cavity doesn’t allow water to transfer to the surface behind it. The problem is that if the bricklayer is not careful, globs of mortar (also porous) can bunch up behind the brick and fill the cavity in spots, becoming a bridge for water to travel into the home. If the material behind the drained cavity is also porous, there can be problems.
Then there is the problem of “trapping” liquid water or water vapor inside the wall, and this can cause mold to form. If you see mold forming inside the home on a wall where there’s a brick wall outside, it needs investigation.
We noticed a new invention called “Mold-Dry” (Schimmel-Dry in German), which are infrared heating panels that claim to dry out a masonry wall so that mold is stopped and can be cleaned. Although we think that the product will do what it claims: dry out mold, the inventors are not correct in saying (under FAQ) “The mold dies from drying and can then simply be wiped off. Since the moisture is removed from the wall, no new mold can form.” We do believe that yes, mold does require moisture, but the process of removing the mold on masonry is more complex because the rough surface doesn’t facilitate “just wiping off” and as shown in some of the diagrams, major mold problems should not just be “heated”. Where does the moisture go from the heated wall? Into the air…heat alone does not get rid of moisture. If there’s no airflow or dehumidification in the room where the heating elements are, using heat will make the air more and more humid, which makes mold able to grow in other areas. Applying heat just causes moisture to flow from one area to another, as the answer to another question implies:
How does Mold-DRY work when new moisture is constantly being introduced? Again, in the product FAQ, “Mold-DRY heats on the back and front. The heat from the back penetrates the masonry and dries out the wall through capillary action. A wall dries through capillary action, like blotting paper. No matter where you start drying the blotting paper, the moisture will move to that spot and dry there. The heat produced at the front forms a heat blanket in front of the wall and supports capillary drying.
Whether moisture is coming in by direct contact or water vapor in air, it’s paramount to address the root cause of the moisture coming in! In the case of basements, it’s necessary to do drainage work to get water pressure (from surrounding soil) off the basement wall (see our article). In the case of brick or masonry walls above ground, it’s necessary to establish a drainage gap and vapor barrier on the interior wall (check out our article on air barriers and vapor retarders). If you just use heat to draw moisture into the home and release it inside, the cycle will not end there, because the moisture is just on a one-way transport into the home.
Another “quick fix” is dry-fogging. Some “mold abatement” companies will promise that their treatments (usually a couple hours) will remove mold and keep it from coming back for a specified period of time. In actuality, dry fogging only inactivates surface mold temporarily, which will resume growing once the air is clear and moisture continues to flow into the substrate.
We wish that there were “quick fixes” for mold on masonry walls, but in most cases they take good, thorough investigation to find and stop the water source, because throwing bandages like heat and fog at mold do not stop the moisture source. If you have a beautiful brick wall that you want to save, It’s worth it to make the calls and get several opinions before deciding how to proceed on a permanent solution that will keep your home’s aesthetics AND keep you healthy and comfortable.
