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RH and MVER Concrete Moisture Conversion table

I found this conversion chart on a blog and wondered if anyone else had seen this and if it's accurate?

"<75% would be equivalent to <3 lbs/sf
76%-85% would be equivalent to 3-6 lbs/sf
86%-90% would be equivalent to 6-12lbs/sf
>91% we are going to want to look very closely at the floor before moving forward"

I found it at this blog: http://www.florock.net/blog/2010/06/09/concrete-floor-coating-2010

It is not accurate. The numbers are not compatible. They measure different things and IMHO ASTM 1869 doesn't provide a valid test to start with. It is just the best option available. Run a cal cl test on a piece of glass. You'll see.

There is a reason Perm Ratings are done with ASTM E96 not F1869.

There is NO CORRELATION between RH and MVER.

Think of it this way:

You have a dry slab, 50 years old, suspended, RH is 55%.
You wet that slab for 24 hours, flood it.
The slab RH is still 55%, the surface water soaked in 1/4" to 1/2" or so.
A CaCl test will read about 12lbs placed on that wet surface.

Conversely a slab in a very dry building laying on a wet subsoil can read 3lbs MVER because the surface is very dry, but the lower portion of the slab is very wet. RH readings can easily reach 90%+. Cover that slab with a moisture sensitive flooring and the concrete will continue to absorb water and RH will climb even higher.

I have personally seen these scenarios, they are very real.

JD Grafton
Concrete Answers for Flooring Problems

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