vapor permeance study

Archive of Older Topics Archive - Product Discussions #5
1

What I think is interesting about this study is the effort to establish a critique of building product manufacturers’ published data based upon what is apparently a thoroughly-formulated, and rare, blind test supervised by a reputable industry expert.

Most of us rely every day upon manufacturer’s data. If it appears in a nice chart, with ASTM numbers, it looks good to the majority of people selecting and approving products in the industry. My experience a decade ago digesting a library of national manufacturers’ product data for a publishing company was that nearly 20 percent of the data were simply wrong: units not corresponding to test standard reporting requirements; order of magnitude errors in numbers; IP/SI conversions with wrong units or numbers; and an accretion of clerical errors. This was before any analysis of the bigger issues, such as: Is this the proper test? Was it carried out on a production sample or a laboratory-selected sample? Does the data reflect ongoing QC testing, or is it based on ASTM X 999 - 1972?

I have no doubt that if a similar type of test program was conducted on other types of building product materials that the data could be as scattered as they were in this one. As David thankfully asks above: how much does this matter? That’s up to the specifier to understand, but at a certain point, it does.

My thanks to Ron for his patience in helping guide the discussion above, which I think is a critical one for our profession. While we are all schooled to be critical of marketing pitches and likely respond negatively to some manufacturers’ overzealousness, there are times when we need to hear what they have to say, such as when consensus standards have been watered down to the point that other manufacturers take advantage of the standards to the detriment of our clients’ interests.

2

anon seems to protest too much. I’m happy since the products I typically default to all seem to be well within an acceptable range.

Having worked at a soils testing lab I can tell you using the same tests at different testing labs and even different machines can produce different results. That’s why most standards list ranges instead of exact numbers. Length of time since last calibrated, temperatures, relative humidity, whether the tester is drinking a cup of coffee, or someone is walking by just as you’re running the test can all have impact on the results.

Do manufacturers choose which test will yield them better numbers? Of course they do. Do some tests possibly favor certain materials? Probably. Does anyone believe that no one would know that the bright yellow plastic sheet being tested was Stego Wrap? Of course not. Maybe that’s why a food wrap testing lab was chosen instead of one more accustomed to testing underslab vapor retarders.

Do I like Stego Wraps negative advertising? No. Do I like their product? Yes. Will I re-write my spec because they want me to? Of course not.

Anon, unless you identify yourself you have no credibility here.

3

I vote with Ken.
I spoke with the Stego reps here in CA recently and basically told them I wasn’t going to specifiy a vabor barrier ( which is what they are pushing)when I wanted a vapor retarder.
If I need a vapor barrier with a perm rating less than 0.02, I specify waterproofing.

4

I’ve seen many a manufacturer have “colloquial” blind testing (as in this case, with the “buyer” pretending to make personal purchases, fake names ad nauseum) done in an attempt to prove their results as some sort of “standard” and others as deficient. In some testing has been done with NO ASTM methods referenced.

Granted, in this one an actual standard was used. But as Richard notes this testing ventures beyond vapor retarders into waterproofing territory.

OTOH I agree about the lack of credibility of an unnamed person claiming something’s rotten and that the tests were faked, which is just reversing the whole negative approach. For all we know the poster is a rep from one of the other companies.

I don’t think tests were faked - I just think they were handled in a cheesy, underhanded way, providing results that don’t matter in an attempt to make competitors look bad.

When looking at comparative product testing performed and published by a third party the raw results are almost always in the form of certified test reports - I don’t see any indication of that here. That’s not enough for me to say the results are faked, but it’s enough to make me question them.

However - I repeatedly ask reps “What’s the application?” when I start to hear negative selling. If a rep is trying to sell me on comparative product testing the first thing I look for is whether or not the test results have a specific relationship to the product’s use.

In this case the test results are about as important as color retention.

Irrelevant testing ticks me off and generally my reaction is “Thanks - I’ll specify all the companies that met their own published test data - except yours. Because I don’t like your approach.”

I spent many years in sales management, and one of my few strict rules was “negative sell any competitor and you better be prepared to submit a job application to them, because you’ll NEED a new job”.

There are enough problems in the construction industry without manufacturers going postal on competitors with irrelevant testing (no matter how accurate) and creating bad blood.

The line I found especially annoying was where manufacturer arranging the testing and publishing the report claims to have no official public opinion regarding it.

THAT statement I call BS.

5

Good points Jim.
I have to wonder if this ‘report’ would have seen the light of day if Stego’s products had not ‘performed’ so well

6

I just saw this thread and I did see the “study” some months ago. I thought the results were interesting BUT as the “professor” was to have written this “report” there were SO many lapses in scientific procedure, writing style, sourcing, etc. that I began to have serious doubts as to it’s authenticity. In fact so many that I tossed the report.
I do have a degrees in Anthropology and in Sociology and a minor in Psychology. I took many classes in experimental design; research methods, report writing, and statistics, and even after 30 years of fading college memories, that report stunk.
Leaving vapor retarder/barrier, and which standard to use aside, just the quality of the writing scared me. The author is no scientist I would ever trust.
Id give examples of the bad procedures/writing but as I said I thought so little of the thing I tossed it.
Get me the professors name and number and Ill tell them that to their face.

7

To begin with. there was nothing blind about this test. Stego has been doing business with Mocon Industries for years. The reason for this misleading report is to try and gain back lost market share. Stego is a MARKETING COMPANY, they do not manufacture any of their own products so they are having a difficult time competing in the market place. They are competing against actual manufactures of the products. Several have ISO 9001 certified plants and have been in the construction industry for 40 plus years. If you look closely at Stego’s literature you will see that Stego has the worst test results in the industry. Their puncture resistance barely passes ASTM E 1745.The puncture test procedure used takes 8 samples of material and test each one for puncture and then takes an average and that is the puncture resistance Test. There is a 20% variance in material. So what that tells me is that 50% of Stego’s material does not even meet ASTM E 1745. No plastic membranes puncture, permeance is consistent through out the membrane. Fact. I would be more than happy to answer any questions regarding this post.

8

Stego’s recommendation has been to change the products we specify. As supporting evidence, they refer to the Clemson Study. I contacted the manufacturers of the products I was asked to eliminate, and asked for test reports from independent testing agencies to verify their published properties. Thus far, I have received information from two of them; the results are greater than, but very close to 0.01.

I found results of another independent study, this one commissioned by CETCO. I think this one is more interesting than the Clemson study, as it looks at the variation in test results. The discrepancies suggest that the test results have little meaning.

A related problem is what the manufacturers report. If they send samples to three labs and only one of the labs reports the material passed the tests, that’s the report they’ll use; the other two will be ignored. (More evidence that what we produce are faith-based specifications.) Still, that’s all we have to go on, so unless we want to pay for testing, we’ll have to accept what the manufacturers report.

I asked our CA group what our experience has been with flooring failures. They report that failures generally happen within a year, often within a few months, and they occur both on slabs on grade and on elevated slabs. Problems associated with vapor retarders would not be apparent until the concrete has dried, and the fact that elevated slabs also have problems - without vapor pressure from below - suggests it is the initial water content of the concrete that is causing the failures, rather than inadequate vapor retarders.

Because of the risk of problems with flooring adhesives, most of the projects I have worked on have included a surface-applied vapor retarder. With the exception of one project, for which the manufacturer of the surface-applied vapor retarder admitted they had shipped faulty product, I am not aware of any flooring failures when the surface-applied vapor retarder is used.

While Stego may have the best perm rating, note that their puncture resistance barely passes the E1745 requirements, while all the others I specify exceed it by a comfortable margin. One might argue that puncture resistance may be more important than perm ratings that are marginally higher than Stego’s, leading to elimination of Stego from the specs. I wonder how they would respond to that.

To set the perm rating at 0.01 would eliminate products that have performed well for us. And, setting it too low runs the risk of having a specification that might not be met due to variation in test results.

9

To support the suggestion that the problem has not been with inadequate vapor retarders there have been tests that show the permeability of concrete is less than the limits specified by flooring manufacturers.

10

Mark:

What suggestions would you suggest be made to concrete specifications pertaining to or improving the normal permeability of concrete?

Do flooring manufacturer’s permeability requirements vary that much?

11

I am not claiming to know the answers but it is my belief that the causes of the problems are not necessary what we have been told they are. My cynicism suggests that the lack of a membrane under the slab was a convenient scapegoat and the flooring manufactures setting criteria that was hard to impossible to meet was an easy way for flooring manufacturers to avoid responsibility.

If you want to reduce permeability of concrete I would suggest the use of fly ash and or Xypex. If you use 0.5% or more reinforcing steel in slabs the cracks should be small in size. Small crack width allows Xypex to cure the crack.

ACI 318 has an Exposure Class P1 where low permeability concrete is required. If this exposure class is specified the water/cementitious materials ratio must not exceed 0.5 and f’c>= 4000 psi.

If you have a specific permeability target there is an ASTM laboratory test which might be used to qualify the mix design. This test should not be used to determine acceptance of in place concrete. My guess is that if you go this route you will have trouble getting the data from concrete suppliers.

In some sense attempting to control permeability without having quantifiable criteria and test procedures suggests that maybe we really do not yet understand the problem.

If the problem is the PH of the concrete reducing the permeability will not necessarily help.

12

If I knew that slabs on grade were going to be of a satisfactory quality, I would suggest omitting the underslab vapor retarder. The fact is, however, that these are not really “structural slabs”, and are especially succeptible to cracking due to shrinkage and ground movement. It is my understanding that the sheet plastic vapor retarders do help with resulting problems.

I do agree that many moisture issues are the result of water in the concrete that remains after full hydration. The best evidence of this is that some flooring systems will have issues over upper floor slabs composed of lightweight structural concrete on metal deck. These floors have a hard time getting to the point of being dry enough to meet requirements for some flooring. This is clearly NOT the result of ground water vapor.

13

Mark, Locally, concrete suppliers have estimated the use of “Xypex” to ADD around $42 per cubic yard of concrete.

14

Xypex, and other brands of crystalline waterproofing, does nothing for vapor permeance in concrete.

15

I do not like Stego Industries tactics in this matter. However I am not convinced that bad marketing tactics are always directly related to a bad product. We specify the Stego Wrap and we have had good luck with it to date. (knock on wood)

Of course the downside of better barriers is that slabs on grade can no longer cure it two directions. This can create real scheduling issues on fast track projects with moisture sensitive flooring products. There are a lot of different methods that can be used to try and diminish the problem but the real cure is still time. In an effort to eliminate or reduce the time factor there are a lot of products that are being pushed to help with this. I suspect we will continue to hear about floor failures in the future as some of the “solutions” prove to be less than advertised.