Need help with my home's concrete slab and moisture

[Jennifer Sullivan]

We recently discovered we have moisture problems with our slab. We started to remove some of our flooring and discovered mold. Apparently one of the previous owners must have glued down wood and when they ripped it up, they did not clean up the glue. The put plastic down and then laminate. Turns out we have moisture wicking up and mold formed on the glue. We had it remediated and now just have bare concrete. We did a calcium chloride test and it came back with 20 pounds of pressure. Our neighborhood has high water table and I have been told the homes were built without vapor barriers. We plan to put down tile, but don't know if we should seal the floors first, put down a membrane or if there is another solution. Most of the sealers that have been recommended to me by various flooring companies say not to use with hydrostatic pressure. We live in Florida, slab above grade. Please help - We are at a loss. Thanks in advance!

[Brian Hannigan]

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[Scott Patterson]

We recently discovered we have moisture problems with our slab. We started to remove some of our flooring and discovered mold. Apparently one of the previous owners must have glued down wood and when they ripped it up, they did not clean up the glue. The put plastic down and then laminate. Turns out we have moisture wicking up and mold formed on the glue. We had it remediated and now just have bare concrete. We did a calcium chloride test and it came back with 20 pounds of pressure. Our neighborhood has high water table and I have been told the homes were built without vapor barriers. We plan to put down tile, but don't know if we should seal the floors first, put down a membrane or if there is another solution. Most of the sealers that have been recommended to me by various flooring companies say not to use with hydrostatic pressure. We live in Florida, slab above grade. Please help - We are at a loss. Thanks in advance!

Wow, you have a mess! But, you already know that… I have seen homes like yours before, and the problem was never really solved to the satisfaction of the owners. If you think about it, you can only seal between the wall, you can't seal where you have walls, etc. So this leaves a good amount of the slab unsealed. It is those areas that are unsealed that then become the problem. Hydrostatic pressure will force the water to the unsealed areas as it is the least path of resistance. Maybe somebody will chime in that has some better ideas. Right now I honestly don't have much more to offer….

[Jeff Zehnder]

You may want to consider relieving the moisture and pressure from the exterior with a positive drainage system if the lot grading will allow. Once that is done you can re-check the moisture levels inside and if they are still high you will need to install flooring that breathes or is permeable so the home and HVAC system can remove the moisture during normal use.

[Garry Sorrells]

20 pounds is excessive. Normal maximum for most flooring application is less than 3 or 4 pounds depending on material.

At your rate I would question if any sealer would actually create an adhesion to the surface and actually work. Grinding down the existing floor surface and applying hydraulic cement may be suggested to you but there is the problem of cracking.

You might look into getting a vacuum system engineered to extract the moisture from underneath the slab.

Then there is a possible idea of using Schluter Kerdi Membrane system in combination with a wood/tile/stone floor covering. You might try a test area (3'x3') by installing the Kerdi ( Thinset-Kerdi-thinset (no tile) ) and then testing for moisture penetration, you might have to increase the area to get a better test result. The Kerdi would in theory seal the floor and create a barrier for a floating engineered wood floor. Just an idea, can not say if it would work.

[Ken Amelin]

20 pounds is excessive. Normal maximum for most flooring application is less than 3 or 4 pounds depending on material.

At your rate I would question if any sealer would actually create an adhesion to the surface and actually work. Grinding down the existing floor surface and applying hydraulic cement may be suggested to you but there is the problem of cracking.

You might look into getting a vacuum system engineered to extract the moisture from underneath the slab.

Then there is a possible idea of using Schluter Kerdi Membrane system in combination with a wood/tile/stone floor covering. You might try a test area (3'x3') by installing the Kerdi ( Thinset-Kerdi-thinset (no tile) ) and then testing for moisture penetration, you might have to increase the area to get a better test result. The Kerdi would in theory seal the floor and create a barrier for a floating engineered wood floor. Just an idea, can not say if it would work.

I'm trying to figure out what a vacuum system under the slab is??

[Garry Sorrells]

I'm trying to figure out what a vacuum system under the slab is??

Similar to Radon mitigation system except that you are after moving a greater volume of air.

[jon dyer]

Good Afternoon, Jennifer -

I just read your post, and wonder if you ever figured out a fix to it.

We live in Tampa, and I think we're experiencing the same on our garage floor - and possibly throughout the house (?).

I'm not sure what the fix would be. I'm reading about a few different approaches (grading the property, installing drains. I've even heard of installing a pump to relieve the pressure. Any insights you have would be appreciated.

Thanks, Jon

[jon dyer]

Hi Jennifer -

I read your post and was wondering if you ever arrived at a fix for this problem.

We live in Tampa and I believe we are experiencing the same.

The neighborhood was built in a low area.

We have heard suggestions ranging from grading the property, to installing drains to installing a pump to relieve the pressure (?).

Any insights you have learned would be appreciated.

Regards, Jon