Stephen Perrera, Owner Of Top Floor Installation Co. and native Tucsonan since 1955 has been in the flooring trade for over thirty-two years. He is licensed, bonded and an insured state of Arizona Flooring Contractor and detailed troubleshooter who performs moisture testing and floor failure analysis, installing a variety of floor coverings. Top
Measuring Moisture Emission Rates and Topical Moisture Vapor Retarders
I certainly do not call myself an expert in moisture emissions testing on or in concrete slabs. But there is much confusion in my little ole installers mind.
It appears that ASTM does not want or suggest emission testing over the top of patches, SLC's and coatings. Meaning... they want it so you have to take the word of the manufacturer of the moisture retarder that their product will perform to their specs.
Hmmm, just wondering if the moisture mitigation industry pushed that part through. I can see the part about not testing over patches and SLC in a way. But this is not helping me determine what the quantitative mver is that's coming through my topical trowel on vapor retarder after application. Yes, I would like to know.
Seeing that the industry is headed towards exclusively performing rh insitu testing..... emissions out the top of concrete slabs do not seem to be a primary concern anymore.
So, when you're doing a F-2170 test and it is borderline rh% they are telling you what as far as potential emissions are concerned? That the flooring will be fine, just enough moisture vapor emissions to not effect the flooring?
I do realize that some labs have done tons of research on this with blocks of concrete over tubs of water. But you know what the real world vs lab studies can sometimes be skewed and biased.
If you're using a trowel on vapor retarder and the manufacturer states it reduces emission rates from 10lbs in 24hrs per 1000sf down to 3lbs...does it matter if you test afterwards? Will they stand behind their product and pay for everything? Is 3lbs safe? Same with a 75% rh in the slab, is that safe or not safe? Sensor drift can be + or - 2%. CaCl tests can vary just as much if not more.
IMHO it's the emissions rate and alkalinity, and the relative humidity content of the slab that's going to bite you. Why has no one found a correlation with emission rates to rh% in a slab? No one denies it is the emission rate that effects flooring and produces higher alkalinity.
They say, emission rates have no correlation to rh and vice versa. But the question arises; then why do the manufacturers of many topical trowel on retarders and coatings specify the 3lbs/24hrs/1000sf in their literature?
Who are you going to believe and what testing will you do to protect yourself?
It appears this topic has sparked a lot of discussion over on LinkedIn forums. Many experts refer to the ASTM E96 method as to how these films are tested for accuracy. This is how they determine the vapor movement through the specimen.
So a friend of mine called and was also just as confused. Let's call him Carl. Carl did a little research and found that one of the ways the coatings/films are tested in the ASTM E96 is in fact the desiccant method. The desiccant is..... that's right, Calcium Chloride.
Read what Carl sent me below and make up your own mind. Should you stick with one method of moisture test or do both the ASTM F 1869 and the ASTM F 2170. I am still not 100% sold that only doing a rh test is enough. There are so many admixtures and types of concrete surfaces out there that affect the emission rate that it can make your head spin.
From Scope 1.1 as I read it. "Two basic methods, the Desiccant Method and the Water Method, are provided for the measurement of permeance, and two variations include service conditions with one side wetted and service conditions with low humidity on one side and high humidity on the other."
However later in Section 4 it states:
4. Summary of Test Methods
4.1 In the Desiccant Method the test specimen is sealed to the open mouth of a test dish containing a desiccant, and the assembly placed in a controlled atmosphere. Periodic weighings determine the rate of water vapor movement through the specimen into the desiccant.
4.2 In the Water Method, the dish contains distilled water, and the weighings determine the rate of vapor movement through the specimen from the water to the controlled atmosphere.
The vapor pressure difference is nominally the same in other methods except in the variation, with extremes of humidity on opposite sides.
Kind of confusing isn't it?
I never really paid much attention to this standard because I usually state that it is not applicable for flooring. This however has opened my eyes a little more.
Edited by Admin 11/2/2011
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