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MMS- Are some unreliable with high RH?

Hi all. Apologies if this has been covered elsewhere-

We recently consulted on a timber flooring installation moisture-related failure, where a vapour barrier was applied.

The manufacturer subsequently changed their spec sheets to stipulate that, if the moisture content was above a certain level (yes, I said content, not RH- the standards here still make it optional to use either criteria), two coats of their barrier are required instead of the previously stipulated one.

This was an admission of non-performance by the manufacturer and, to their credit, they copped a six-figure sum in remedial expense.

Is there a point where some MMS's will not guarantee performance where the RH is too high? Even if they wouldn't admit to it, do some installers here use a sort of "best-practice discretion"?
The problem with socialism is that you soon run out of other people's money.
- Margaret Thatcher


All MMS systems have limits. When it comes to MMS systems there are any number of different varieties and qualities.

I'm surprised that any manufacturer would pay out based on a change in specs. I have found that in the USA spec sheets at the time of install is the basis of installation in the event of failure.

Usually the MMS systems have a 'spread rate' that is used at different moisture levels. I.e. X gal/sf per Y rH or #'s.

... and there are plenty of MMS systems that no matter what you do it will be the mistake of someone else.

And re: your title.. there absolutely are some MMS' that are unreliable. As a flooring distributor there are products which are not allowed under my floors. So much so, that I have passed on large orders where the Architect or Construction Manager or General Contractor insists the MMS is fine. My brand is worth more than any individual order.

Thanks Evan. I suppose I'm trying to build the alibi for regular testing regimen- too many contractors still say "Don't worry, we're just gonna slap down a vapour barrier".

The manufacturer in question (I won't name them, and I don't expect anyone on this thread to name anyone in these types of discussions!) fully believed from their R & D that their product was a one coat system. The fact that they responded to a failure by tightening their specs, when it means they will possibly sell less product, not to mention wore a lot of cost, is one of the reasons we will continue to deal with them.

Some guys put down plastic sheeting, then plywood, then overlay timber flooring. Is this a reliable mitigation against slab moisture?

The problem with socialism is that you soon run out of other people's money.
- Margaret Thatcher


In the USA the current hardwood standards that I deal with are via the mfma (since I do gyms). The mfma requires rh testing to read 80% for the system you describe and 75% for glue down systems.

We put the equivilant of 15mm stego wrap under our wood systems and loose many bids vs the guys who put 6mm home depot poly. However, I wouldn't change, it is cheap insurance.

In California the wood flooring installers are really poor. I even know some who still rely on the tape down plastic method. All low bid and run. I even know some who will not use rh tests and use cacl tests to get low test results. As if they put their fingers in ears and yell la la la la la

I would say a vapor membrane on top of concrete is standard. Quality varies by product and contractor. But mms systems are the exception except where there is high moisture when you do get mms systems.

Great question Pat, it is one that confuses me also.

The specs and requirements of MMS manufacturers I am familiar with all vary somewhat. Some will not warrant their product unless there is a vapor retarder under the slab. Some limit RH to 95% or less. One is limited to 98% RH. Many warrant to any RH, but will deny coverage because the alkalinity is too high.

Why am I confused when these numbers seem so clearly defined? The numbers are not firm. The MMS I mentioned that is good to 95% RH is a two part 100% solid epoxy system. I mentioned to my factory rep that I had a project with no vapor retarder and a history of failure. These are the worst possible parameters and RH values can reach 99%. No worries I was told, the technical team has approved the use of our MMS on that slab. Huh
JD Grafton
Concrete Answers for Flooring Problems

Ah yes, well, I haven't scanned all of the Manufacturer specs on the products I deal with. They don't seem to stipulate any RH limits, and can "withstand up to 250 Kpa of hydrostatic pressure" etc.

I have another question which I suspect is not so great: In my industry we deal with "vapour barriers", the most common obviously being Bostik Moisture Seal. Most are water based epoxies.

When you guys talk about Moisture Mitigation Systems, such as Koster and Ardex, are they different animals or just different brands of the same thing?
The problem with socialism is that you soon run out of other people's money.
- Margaret Thatcher


Koster and Ardex, along with Mapei, BASF and several others are different. They are 100% solids two part epoxy systems.
JD Grafton
Concrete Answers for Flooring Problems

To give you an idea:
ASTM E96 Bostic Moisture Seal's Perm Rating is: 0.12 g/24 hrs/M²mmHg @ 32° C and 50% RH
source: http://bostik.com.au/construction-trade-products-catalogue-sheet-28565-moisture_seal-m-0-g-0.html

ASTM E96 - Koster VAP perm Rating is: 0.024 grams h-1 m-2
source: http://www.kosterusa.com/files/us_en/6.035-VAP-2000.pdf

And as a benchmark:
ASTM E 1745 - Stego wrap has perm: 0.0084 (but I can't find metric #'s for it)

**Section 7 of ASTM E 1745 specifies the testing conditions and allows for either of the following test methods: ASTM F1249 or ASTM E96.


And of course the permeability of concrete can vary, but I have read that 4" of concrete has a perm rate of less than .8...

The numbers quoted for perm ratings are all over the place aren't they? Makes it hard to compare. I believe Bostik reports grams of water over 24 hrs over a square meter, and then that is at 50% RH. What does that mean? 50% difference between slab and ambient?

Koster VAP1-2000FS which I use is an average of .05 grains /hr/sf. A gram is about 15 grains....
JD Grafton
Concrete Answers for Flooring Problems

(11-06-2011, 06:19 PM)Rubensgt40 Wrote:  Some guys put down plastic sheeting, then plywood, then overlay timber flooring. Is this a reliable mitigation against slab moisture?

Yes it can be, I do that all the time for floating floors. But if I am using a solid timber or the slab is below grade I take it a step further and use something like Bostik MVP4 first, then the plastic, then plywood and then 15lb roofing felt and finally the timber.

I have also tested these systems before hand using the Rapid Rh, and even going so far as to do a few F 1869 tests on top of the MVP4, even though the ASTM guru's say you cannot do that. Not sure why because if you take a close look at ASTM E 96 they use a dessicant to evaluate the product they are testing, and that dessicant is.....calcium chloride. Kinda confusing huh? Whats more confusing is that many of these people who frown on the old F 1869 test will always refer to the ASTM E 96.

Stephen Perrera dba
Top Floor Installation Co.

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