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leob 05-19-2008 05:28 PM

Mold prevention over concrete slab
We discovered that ground moisture getting through the cracks in our concrete slab foundation was causing mold to appear in the carpet. Before installing new carpeting, we need to be sure that we are well protected from mold appearing again. I'm thinking of sealing the cracks with a silicon caulk as that might maintain a seal despite movement of the concrete. In addition, I think that it would be advisable to cover the concrete with something to prevent any moisture from getting into the carpet. Does anyone have knowledge and experience with this problem?

angus242 05-19-2008 06:57 PM

This starts to get into a gray area. For your specific situation, you could use a product called RedGard. It comes in a liquid form and would get rolled over the slab. Once it's dry, it will be a moisture barrier. Here's where it gets tricky. You CANNOT put any type of material over this that can't breathe. If you used some kind of moisture-proof or vapor barrier on top of the RedGard, you'd create a moisture sandwich and have the same problem all over again. As long as you use padding that breathes, you can carpet again and your problem should be solved. However, don't plan on putting some kind of vinyl product or a floating floor w/vapor barrier on that floor ever.

leob 05-22-2008 09:59 AM

Thank you very much for getting back to me so promptly, Angus. I couldn't respond until now as there was a website snafu with my registration. You gave excellent info but what gives me pause is that RedGard and other products require that the smooth slab be roughed up and we've just finished painting all the walls and ceilings. If I can determine with any certainty that the water source was from a leaky hose bib outside, I might just settle for sealing the crack (without using an angle grinder first). I need to inquire on what the objection is to just using a silicon caulk for that. Just curious - how is moisture to get into the sandwich you mentioned? Thanks again.

angus242 05-22-2008 10:12 AM


Originally Posted by leob (Post 125028)
Just curious - how is moisture to get into the sandwich you mentioned? Thanks again.

Condensation. Warm room, cold slab or vice versa. Condensation can occur between 2 vapor barriers but then cannot evaporate properly.

sevver 05-22-2008 10:13 AM

You should really try to figure out what the water is from, that is what you should do. is this in a basement? Sounds like you are just talking about a slab floor at the main level. Is there a foundation around the slab? Could it be that something is leaking under the slab, being contained by the foundation, and coming through the floors? I would wonder if maybe a water service leak is occuring, or a sewer backup is brewing. Don't try to cheat, find out what is wrong.

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