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Mold Growth in CMU cells after flood

Mold Growth in CMU cells after flood

Mold Growth in CMU cells after flood

First, let me know if this is not the correct place to post this. I see this as an environmental issue and did not want to cross-post to the structural forum.

I have a building that was flooded. The building structure is CMU load bearing walls.

A proposal was made to place drill holes into the CMU to relieve the walls of excess moisture and prevent mold growth. This seems odd to me as I would think it would need a food source in the cells of the wall to grow mold, and that the walls would simply dry out themselves.

What are your thoughts, is this good practice or overkill?

RE: Mold Growth in CMU cells after flood

Take a look at FEMA's Technical Bulletin 2: Flood Damage Resistant Materials. Pay particular attention to Table 2, Foot Note 1 (related to hollow CMU).

Based on this, one of our local municipalities no longer allows hollow CMU below DFE.

So drilling the holes may allow the water to drain out faster and minimize contaminants from being absorbed by the block, but you'd need to go back and fill that block. A closed cell insulating foam is often a good option as it has a negligible effect on foundations from weight increase.

Mold can absolutely grow in the CMU. It's not an ideal environment, as concrete provides very little in terms of food for the mold. But it's not impossible. Especially if those flood waters brought organic material in with them. Even at the microscopic level, I think it could be enough to get some spores going. (Not a mold expert, though, so you may want to contact a company that specializes in mold and fungal control.) In some ways drilling the hole could make this worse as it would allow 'food' to come in through the hole. Again, filling with a closed cell foam would mitigate that substantially.

RE: Mold Growth in CMU cells after flood

Thanks Pham. Great response as always.

I also found FEMA Tech Bulletin 7 (2022), specifically section 7, discusses ungrouted CMU walls.

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