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Burnished vs Floated Slab (Stego)

Just found this: http://www.us-concrete.com/aridus/DryingofLightweightConcrete.pdf

A great look at RH in slabs in unconditioned environments. Obviously a sales piece for Stego/US Concrete's Aridus but still valuable.

What is interesting is this is SO controlled that it shows something. We all know that 100% of those slabs will not fail at 80-90% RH if the CaCl is in the 4-5 range. Yet the perspective is that they will.

I think there is a LOT of 'safety margin' in manufacturer specs of 75-80%. I bet there has been very little real research by adhesive companies as to what really works and what doesn't. I've never seen a single study put out by Mapei, Bostic, Parachem, etc....

I don't think the adhesive people want us to see their studies.
Stephen Perrera dba
Top Floor Installation Co.

Think of this:
Many adhesives are completely waterproof. Yet they fail.

When you have a high moisture slab, you have the potential for high alkalinity at the glue bond horizon, either at installation or, and here's the kicker, sometime in the future.
Low moisture slabs have less potential for high alkalinity at that glue bond line.
Are the recommended RH rates artificially low? Of course. Manufacturers need to build some cushion in for varying testing techniques and equipment, and some extra fudge for a safety factor doesn't hurt them either, unless their competition bumps their minimums up, which we have been seeing as more field results prove performance over time.

Adhesive manufacturers are walking the line between market share and failure rate. Some are raising their minimums to 90% or even 95% RH and then putting a low pH limit in the warranty requirement. So when the adhesive fails, we're told it's because the pH is too high. Well we knew that already, but where did the high pH come from? From moisture movement, due to the high moisture content, which we verified with our RH testing!

Do those adhesive companies know that high moisture slabs have the potential for high alkalinity and a real potential for failure due to alkalinity??? Of course they do. And that's why the warranty is written the way it is. Remember warranties protect the manufacturer Wink

Be careful with those 'breakthrough' adhesives that guarantee they'll work on high moisture slabs. Wink
JD Grafton
Concrete Answers for Flooring Problems

Yet some very reputable people on the moisture testing front have said there are adhesives out there that can tolerate exceedingly high RH.

But your point is well taken. Tandus recently did that. They say their material has no moisture limit. But they say that there is a pH limit.

I have also begun to see some loose lay flooring getting bubbles. No adhesive but they are getting bubbles. Why? I dont know.

Bostik Ultra_Set Single Step says only dry to touch, no limits. Nothing about alkalinity/ph.

Stephen Perrera dba
Top Floor Installation Co.

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