Mildew under carpet - installing laminate

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Old 09-18-18, 07:16 PM
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Mildew under carpet - installing laminate

Greetings!

I just started the process of replacing the carpet in my house with laminate. One of the rooms I did with glue down engineered hardwood, and it looks great but I simply can't afford the material and time cost to do the rest of the house with the same flooring. I live in Texas, so this is a ground level slab built in the late '70's.

Anyways, I removed the carpet in the first area that I am prepping and found that there is mildew under the carpet pad. Now that the carpet and pad is up, of course there's a strong mildew smell all through the house. It's no surprise, the last room I did had the same thing. I was able to treat the concrete to get rid of the mildew, then used a very expensive glue that's supposed to have a vapor barrier in it, but parts of the floor have still buckled up slightly.

The floor is not wet, per se. There is just enough moisture coming through the concrete that it will grow mold/mildew under probably whatever flooring I put down. I'm still planning on a vapor barrier underlayment and laminate flooring, but what is the best way to get rid of the mildew and then seal the concrete? Is there some sort of coating that prevents mildew from growing? Also, is the slight amount of moisture anything to worry about affecting the wood frame of the house?

I am hoping there's a way to disinfect/treat the concrete, then something I can apply so I don't have to worry about mildew growing between the concrete and the underlayment. I know if I had a lot of moisture coming through the slab I would have to lay tile to prevent further issues, really hoping to avoid that.

I've heard of redgard, but I always thought that was just for waterproofing. Would that be the best option to paint my slab with before putting the flooring down?

Thank you!
 
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Old 09-18-18, 07:45 PM
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It is my understanding that a product like Hydroban, similar to redgard, but much thicker can be an effective waterproofing layer. The concern is that mildew needs moisture to be present, therefore, your slab is offing moisture which is deadly to any laminate or wood flooring.

Before investing in a ton of flooring, try to get the moisture under control. Look at the gutters and drain spouts in that area and make sure they carry the water sufficiently away from the slab. I would test that theory and wait through several heavy rain storms before laying laminate. And even at that, you will want the best underlayment vapor barrier you can afford to go under the laminate. One designed specifically for slabs. You then run the vapor barrier/underlayment several inches up the walls all the way around the room and hide that under the baseboard. Kind of making a reverse swimming pool to keep moisture away from the laminate.
 
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Old 09-18-18, 08:06 PM
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Thank you for the fast reply!

I do know that the moisture will be a persistent issue. I have ensured that the gutters are channeling water away from the house, I have installed a french drain, and will be making an open trench to further discourage standing water around the slab, but the water table is still very close to the surface on my property.

The room I just pulled the carpet in is in the dead center of the house, at least 15 feet from any exterior walls. I am going to try the plastic sheeting test, taping a plastic sheet to the slab and checking it a few days later for condensation, but I doubt the moisture problem is that bad.

I don't have a problem using redgard or hydroban before putting the flooring down, my only concern is mildew growing between the concrete and the layer of hydroban... If that's possible at all. For now I'm letting the concrete dry out and I'll be getting rid of the mildew. The areas where the mildew was growing are darker than the surrounding concrete indicating that moisture is present, and I doubt it will be going away. I will monitor it for a few days though.
 
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Old 09-18-18, 08:53 PM
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It is my understanding that one or two coats of hydroban is the equivilent of 6 to 8 coats of redgard. It is used as a crack isolation membrane all the time on concrete. But the hydroban is thicker and requires less coats. So it may seem more expensive up front, but is less in the long run. Get it at a time distributor. Made by Laticrete.
 
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Old 09-18-18, 09:35 PM
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I will definitely check for it at the local tile/flooring stores, we have a couple to choose from. If they don't stock it I'm sure I could probably order it through them for less than shipping would be.

I read elsewhere that in very wet areas (Florida and Louisiana, namely) if the slab is wet all the time that even after sealing and putting a barrier down for the floor it's wise to ventilate the baseboards to allow some of the vapors to escape so they don't go up inside the walls and grow mildew on the drywall. Is that something I should look into? I have no idea how to ventilate a baseboard.
 
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Old 09-19-18, 05:27 PM
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Okay, one other potential road block I've run into. I am cleaning and attempting to prep the concrete for the sealer, and there is quite a bit of overspray from when the walls were painted. It's not coming off easy (at all, really) with a scraper. I can't find specifics online for surface prep for any of the sealers I'm looking into, but I assume paint needs to be removed. Is there an efficient way of cleaning the concrete? And how spotless does it need to be? A friend suggested muriatic acid, but I'm pretty sure it can't be used indoors.

Thanks!
 
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Old 09-22-18, 05:05 AM
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A perimeter French drain should significantly reduce, if not eliminate, problems due to a high water table.

You will need a pit with sump pump that gets rid of the water collected by the French drain.
 
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Old 09-23-18, 08:26 AM
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The problem with any moisture barrier is that mold and mildew can still grow under it. You have to stop the moisture from coming in.
 
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