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Having (let's call it) a discussion with my GF about where the mold is coming from in our shower. My understanding is that mold originates from the wood. To be more specific, the wood gets wet and if it doesn't get dry it will eventually grow mold. Then, the mold will grow through the everything including the cement board, thin-set, caulk, tile, etc... However, it starts from the wood and not anything else. So, if the wood didn't get wet, there would be no mold.

Please correct me if I'm wrong.

I'm asking because we our doing a shower remodel. We already tore everything out down to the studs/framing. And, our shower had mold, and she would like us to replace ALL the studs and the top and bottom plates in the shower because she's afraid if we don't, the mold will grow back. I just want to replace the one's where I see mold. However, she makes a great point that just because we don't see it, it doesn't mean it's not there.

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    Mold spores are in the air. If they land on damp dark(less light) surfaces they will grow. They do not like dry, sunlight, air movement.
    – crip659
    Sep 17, 2023 at 22:19
  • Mold most definitely does not only originate from wood. The interior construction of your walls makes absolutely no difference to whether or not you get mold in your shower - your walls could be made from bricks or concrete and you're would be just as likely to get mold as you do now with wood studs in the walls. It's the environment of the shower (typically dark & damp) and the fact that mold spores are everywhere in the air which lead to mold growing in your shower.
    – brhans
    Sep 18, 2023 at 14:31

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Fungal spores are everywhere. You are breathing them right now, and your immune system is keeping the fungi from growing inside and outside of you. These spores can grow anywhere there's a good substrate (surface.) Showers are constantly wet and with poor air flow because most people don't like the noise of the fan (that includes me.)

A piece of wet wood that already has mold will continue to grow mold as long as it's wet. But even if the wood were dry, as soon as your bathroom walls get wet, spores will land and start growing.

The solution is to keep the bathroom dry after you use it. Use the fan while taking a shower, open doors and windows whenever weather permits, etc.

Mold cannot grow through the cement boards.

I would not change any studs, unless they are rotten. Just let them dry.

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  • While the walls are open, applying a fungicide spray and maybe a sealer isn't the worst idea either. Sep 17, 2023 at 23:18
  • You would not replace the studs even if it had mold on it? Also, If it's not coming from the wood studs and cannot go through cement boards, where else could it be? We use to spray the mold to clean it with commerical products often and it would just come back
    – ptownbro
    Sep 17, 2023 at 23:34
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    If the studs are not rotten, they should not be replaced Sep 17, 2023 at 23:51
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    @ptownbro As I said on the answer, mold will grow wherever there is moisture. Even if you apply fungicide, if the area remains wet, mold will grow back on it. If money is burning a hole in your pocket, you can use anti-fungal spray. But diluted bleach works just as well and is cheap. I like cheap.
    – Cheery
    Sep 18, 2023 at 0:14

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