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High Moisture Levels 1 year after slab poured, residential home

My husband and I purchased a brand new home (slab) in Ga

Slab poured January 10 2012
engineered hardwoods installed April 14 2012
Dark spots/orange peel texture begins to appear in July 2012

Mold present under floor. 4 calcium chloride tests with results of 7 (carpeted room) 16, 16 and 17 were completed December 2012

The builder stated the timing of construction was to blame. Our floors were removed February 22 2013 and small surface cracks were present which seems to indicate a cured slab.

Wagoner RH metered were placed and the first set of readings taken 40 days after the floor was removed and the slab had been exposed ... readings were upper 80s.

One core was taken from our slab in February showing a vapor barrier but uneven bottom of slab. The core was tested and showed strong and normal composition. Water tables were done outside and normal, cameras were run through pipes and no leaks.

Any thoughts on what is going on or what to do? Builder is suggesting re-install once acceptable levels are achieved. We are currently re-doing calcium chloride tests.

Thank you in advance.


Thanks for the detailed outline. It sounds like you have definitely done a very thorough analysis post failure. Here are a couple of questions I would be interested in having answered:

1) What were the pre installation RH and/or calcium chloride numbers?
2) What were the ambient conditions of the environment when the above mentioned tests were completed?
3) What is the nominal thickness of the slab?

That being questioned, her are a few things, based on the information and timeline that you have provided, I would like to bring up:

1) Rule of thumb for drying (not curing) of a slab: it takes approximately 30 days for every inch of slab thickness, once the environment is conducive for drying i.e. window and doors in, HVAC up and going, for a slab to reach an RH% level in the 80's. Your floor was installed four months after slab placement. Was it dry enough at the time?
2) Most wood flooring products will require 75% RH or 3lbs CC readings to be acceptable for installation.
3) You very easily could dry out the top surface of the concrete and get acceptable CC readings for reinstallation. That being said, the RH levels very well could still be in excess. Be cautious when trying to expedite drying.

Here is one question I would like you to think about:

a) Do you want to know what the moisture condition at the surface of the slab is right now or
b) Do you want to know what the moisture condition at the surface of the slab WILL be once you have your floor installed?

Proper RH% testing answers b. Calcium chloride does a.

Last thing would be solutions, based on where your RH% numbers are currently. They do make moisture remediation products specifically designed to encapsulate less than desirable levels of moisture, prior to installing moisture sensitive flooring products. Many of them are two part epoxies.

I hope this helps. Please don't hesitate to let me know if you have any further questions.

Jason Spangler

To add to Jason Spangler's comments, one thing I did not notice...was a quality vapor barrier placed under the slab? By quality, I mean something thicker than a 6 mil poly. If not, Jason's suggestion for a 2 part epoxy moisture mitigation is the only solution for the long term because moisture will continue to migrate from the ground up through the slab. While perhaps a minor detail, if a vapor barrier was used, it was compromised when penetrated to retreive a core sample. This may seem like such a small area, but it will need to be addressed before installing a non-permeable floor covering. At this point, you might consider leaving the concrete open for a few months and installing ceramic or porcelain tile...they breathe and will allow moisture to pass through. Just a thought. Good luck
JK Nixon
Concrete Restoration Services, LLC
Pittsburgh, PA

If the RH probe readings were 80% there is your problem. RH readings for wood 75% or less. NWFA and all wood mfg's guidelines.

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