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Flooring and Carpeting/Laminate Floor and moisture


QUESTION: 9 months ago we had a laminate floor installed. They used thin set and moisture barrier on the concrete foundation.  We just noticed buckling of the laminate.  The installers removed the laminate and found the thin set cracked and crumbling where the buckling was at.  Also found moist thin set in patches along the entire floor.  There was no moisture between the laminate and the moisture barrier. Also could not find any evidence of water coming in from the outside or adjoining walls. The installers will not warranty the work because they say it is caused from water, not moisture.  

Is there anything else that could cause this?  I'm scared to repair the this set and put the laminate back without finding the source of the water.  One more thought, could this be caused if the thin set was not completely dry before they put down the floor?

Thank you for any insight.



A couple of things come to mind here. The first , A moisture test should be conducted with a calcium chloride test kit by the installers prior to the install. If they did not perform this test then the liability does in fact fall on the installation contractor and /or the retail seller.

Now let's say they did perform the test and it passed? It's still possible that at the time of installation the slab was dry as a bone and later in the season the weather (rain or poor irrigation) was heavy enough to cause an issue. Moisture escapes upward as vapor, building pressure and is measured in PSI.

This is often the case with slabs in California, I installed many floors in So Cal. One in Chino Hills had sprinklers that made the exterior so wet the walls were moldy behind the base boards inside. Within 6 months we were called back to investigate.

As I re read your question you say you have various areas of moist thin set. Installers typically use Grey polymer cement floor patch, not thinset. Thin set is used for ceramic tile and it has a very gritty texture due to the sand content and does not spread smoothly. The floor patch we use is portland cement based, dries rapidly within 20 minutes unless it is layered thicker than 1/2"-3/4" then it could take an hour or so. As it dries it changes color, from a dark wet grey to a light dull grey. But it will get dark again if water/ moisture is present. If the patch is white it is a gypsum based floor patch and is not acceptable as of the early 90's by the FCI (floor covering institute)where we get our standards of procedures.

Tell me what moisture barrier you are referring to?? The 3 in 1 foam ? Or an additional product that is applied to the concrete with a trowel or roller and allowed to dry.

When I find the moisture test results in more than 3.0 PSI I will inform the customer to purchase a 2 part epoxy system that is applied to the floor with a paint roller or trowel. This system dries in 12 hours and the next day I can install the flooring. It resists moisture up to 12.0 PSI. You can buy it from these good folks at Dri Tac

BOSTICK also sells another membrane that you can purchase and apply.

Personally I have used both and for laminate I prefer the first recommendation. Less work and easier to use.

Finally, what I don't understand is the installer saying it is water...not moisture. If it is coming up from the slab and not reaching past the foam barrier to the laminate then it is moisture / water / vapor transpiring from beneath. If it were water / urine / drinks /spills from the surface, it would settle on the top of the foam and not reach the slab or floor patch in any significant amount.

Another fatal error installers make is to use a non water proof tape to seal the seams of the foam 3 in 1 barrier. Check that as well.

In California the contractors board and the state law protect the consumer. The installer is always responsible. You can take this to court if you choose.


---------- FOLLOW-UP ----------

QUESTION: Thank you for your quick and detailed response.

Yes it is floor patch, not thin set.

They did not measure moisture at time of installation.

They say it is not moisture problem because after they removed some of the floor patch the moisture content was 2 - 2.5 on the concrete slab.

Even though there is no evidence of a water breach, they say it is water from rains or leak within house and are not willing to pay to put the floor back ($2000).

Thanks again.


If you pursue this on your own a LEAK DETECTION company should be called in to try and determine the possible leak. Then remedied if possible.

If it is just moisture from the slab there are products to stop moisture from transmitting through.


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20+ years flooring installation ...carpet,wood,tile and vinyl. Residential and commercial. I do not sell the products , just install what ever the shop / customer has purchased. I actually love seeing the finished project completed and it gives me great satisfaction to help others acheive that goal. If I don't know the answer I will say so, and then I will recommend another expert for you. I may even research the subject and answer to the best of my ability ...including links to my sources. I wish you all success Chris


20 years as an independant contractor

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