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MMS- Are some unreliable with high RH?

(11-09-2011, 07:28 PM)CC Solutions Wrote:  Pat,
There are some instances where I do no testing before or after. If the slab is on grade and has no vapor retarder and the facility wants to install a moisture sensitive floor there is no reason to test the slab. It has already failed and is not up to the flooring manufacturer's specifications.

I have seen many, many floors fail that have a low MVER. A very hard troweled floor slab has a mechanically sealed surface that will impede vapor release. These floors can measure as low as 2lbs MVER and still fail miserably in a short amount of time. This proves MVER is not a reliable test, and is not an indicator of a slab's readiness for flooring.

Now the ASTM for F1869 has changed in an effort to show a higher MVER. In my mind it's too late, we have a new method of reading floors by using the Wagner Rapid RH. There are far too many variables with MVER that we don't see with RH testing.

Think of it this way. A slab's RH indicates the potential the slab has for failure. If the slab reads 98% it has a very high potential to fail. It is full of percolating hydration and alkalinity. A slab that reads 70% RH has a low potential for failure. It has completed hydration and is stable.

OMG here we go again! SadSad

Jd, that first statement is funny because I go over slabs all the time with wood and just a urethane adhesive like Bostik's Best, that have read in the high 70's with no MMS system underneath and no vapor retarder under the slab. I think it is more about the design, grading, run off from the roof, how large it is etc. Is wood not a moisture sensitive floor covering?

Then in your last statement you state the slab is stable if the rh reading is in the 70% range. So which is it?

I think the Wagner Rapid Rh is an invaluable tool and the best rh device out there but I don't strictly rely on it. Would I go over a slab thats testing in the 90 range without an MMS, most likely not.

Heck I am even leary of the newer one step adhesives that simply trowel on a double layer of adhesives. I did just use Bostik's new adhesive the Seal N Grip and the One Step on a stranded Bamboo but I did test first.
Stephen Perrera dba
Top Floor Installation Co.

Messages In This Thread
RE: MMS- Are some unreliable with high RH? - Ernesto - 11-10-2011, 07:45 AM

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