99% RH in concrete slab

[Floorguy]

Hot water lines, causing a dew point. Seen it myself many times.

Internal plumbing leak.

Built on a natural spring.

Soil high on the perimeter, making it below grade.

[eaadams]

(02-03-2011 12:55 PM)Floorguy Wrote:  Soil high on the perimeter, making it below grade.

Technically, I think the rule is the slab has to be 4" above ground level to even be on grade.

[Ernesto]

(08-22-2010 02:38 PM)mwoody Wrote:  I have a project where 8 Wagner 4.0 RH probes were placed in a 40,000 square foot concrete slab on grade. The slab thickness is 6 inches with a vapor barrier on top of soil. The probes were placed at 40% of the depth of the slab. The slab was placed approximately 15 to 20 years ago. The HVAC has been running for over a month with the ambient temperature at 75 degrees and the humidity between 50 and 60%.

6 of the 8 probes read in the 70% to 80% range and the other two probes read 99%. The two 99% readings are on opposite sides of the warehouse. Any ideas on why the probes would read 99%?

Reading it again, thats a lot of roof. Wheres all the water going outside those walls?

[CC Solutions]

I wonder what Woody found out?

Maybe the two high readings were drilled right through the slab and then the probes were set at 40% depth... I see that more than I care to!!!

[eaadams]

It could just be random error. I have seen many slabs test 99% and a new hole new probe doesn't read 99 real close to original test.

[CC Solutions]

I hate it when we're left hanging like this.

Hope Woody checks in and lets us know.

[mwoody]

The contractor put a sealer down prior to the epoxy surface coating.
Never had any resolution on the 99%. Tried switching out the probes but watched the humidity rise back to 99% by the next day. After the fact we cored the concrete adjacent to the probe installation to make sure the probes were at 40% depth, check. Just another floor moisture issue where the cost to find the conclusion just isn't worth it.

[CC Solutions]

Thanks for the update!!!!

[Ernesto]

I've installed engineered hardwood when the sensors read 85% and had not problem at all. That concrete was so dry it would suck the spit off your tongue. I didn't even use a trowel on vapor retarder. Ask me why.

[CC Solutions]

Please do tell (in your 99th post!!! )