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We're almost at 3lbs MVER, so what if the rH is over 90% ?

I have heard from many GC's, owners and installers: The moisture vapor emission rate (MVER) is pretty low, let's use that number and forget about the rH test!

Sometimes I like to answer with a shocking statement to derail their train of logic. I tell them water isn't the problem! We have hundreds of wonderful waterproof glues. Water isn't the issue!

This statement grabs their attention (well why in the world are we measuring moisture then?? ) and lets me explain further. The concrete slab is a reservoir of alkalinity and salts and moisture that can destroy a glue, even destroy a concrete slab sometimes. What we have found after many years of CaCl testing is that we can get a low MVER reading but still have this highly active concrete slab under the surface just waiting to destroy our floor covering.

RH testing looks inside the concrete to determine the potential a slab has to ever be problematic. If we find a low rH reading, this means the slab has completed most, if not all, of its hydration, the water of convenience is nearly gone, and the potential for future problems is greatly reduced.

More manufacturers are embracing the rH testing method in the US because they have witnessed the faulty logic of MVER testing and may have even had failures on slabs that passed the CaCl test. Recently the ASTM committee for calcium chloride testing (ASTM F-1869) changed the method of test installation intending to create a more open and porous surface of the concrete slab which should result in higher MVER readings compared to the previous test protocol.

The problem I have is nobody has acknowledged the elephant in the room. The CaCl test has no real pedigree, what we thought was a good number according to last year's test (3 lbs / 5lbs) was resulting in failures, now the MVER numbers are coming back higher, is 3lbs still a good number? It wasn't working before, will it work now? When we grind the test site, we alter the surface of the slab. Do we need to alter the entire slab to expect similar conditions before installation?

RH testing reads inside the slab. It was designed to indicate a concrete slab's potential for failure based on the moisture inside. The readings are accurate, stable and dependable, but most of all the readings work. The science behind them is solid. You can trust that a properly conducted rH test will give results you can bet your flooring on, and stake your reputation on.

As for all those CaCl test kits you have left over? Send them up north to me, I use them as sidewalk de-icer in the winter. Tongue
JD Grafton
Concrete Answers for Flooring Problems

Messages In This Thread
We're almost at 3lbs MVER, so what if the rH is over 90% ? - CC Solutions - 07-12-2012, 07:26 AM

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