RH Numbers Rising

[Ernesto]

Quote:For my own edification: Lets say you have slab on vapor retarder. Slab curls. You grind off the top and lay flooring. The bottom of the curled slab is now plenum space? Can H2O travel laterally in that space?

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Can I try and answer that? The vesicular structure in the concrete inhibits the lateral movement of moisture in the slab. But after it moves off the top of the slab it can go anywhere.

[eaadams]

No I mean the bottom, like this:



Image from this: http://www.nrc-cnrc.gc.ca/eng/ibp/irc/ct...s-n44.html

[CC Solutions]

It has been my experience that the vapor retarder moves with the slab. I'm sure that there are no absolutes, so I won't say it always does, and in those cases, yes there would be a transportation medium available for moisture to move laterally.

I think I should just put a Koester MMS on every slab and the world would have no more worries!

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(04-08-2011 04:19 PM)eaadams Wrote:  CC Solutions - have you ever done work in the NW in WA, OR, ID? Seems like a hole I never hear of problems up there but it rains cats and dogs. Do they use vapor retarders direct to slab commonly?

I've worked in Washington, Seattle to be exact, and actually enjoyed many sunny days (lucky me ) Beautiful country out there! Vapor retarders must be on direct contact with the slab, and with all the rain it is hard to dry anything out before a roof is on and the windows are installed. Even then you have hundreds of workers tracking water in with boots in the main hallways.

I always seek out the coffee shops in Seattle.... They have fantastic coffee and seafood. Anybody have a moisture issue in Seattle that maybe needs me to take a look at??

[rthompson]

Moisture vapor travels almost vertically in a concrete slab. It will diffuse off center about the thickness of the slab. It is true the moisture will travel laterally in the blotter layer and that is why the blotter layer recommendation was omitted in April 2001.
Rayt

[CC Solutions]

Thank you Ray.

[eaadams]

"the blotter layer" is the main problem in the West. FYI everyone - I know of a major architect who is now being sued because of their use of it in a 2006 slab. Our instructions removed the blotter layer in 1999. I look forward to getting deposed because it is not the Architect's fault. It is the structural engineer to whom they subbed out that work. I can't wait to throw him under the bus.

Even CalGreen (the new building code) still allows for it if the slab is "designed by a structural engineer". Well ... I can't wait to see one of these engineers get sued. They are the ones who are the cause in fact for 80% of the floor failures we have had to deal with. Not the flooring sub, not the gc, not the architect, not the curing compound, not the adhesive, not the material suppler, the engineer should be blamed.

It will be interesting to see what gets decided. But, it will probably settle out of court.

[CC Solutions]

(04-09-2011 01:38 PM)eaadams Wrote:  "the blotter layer" is the main problem in the West. FYI everyone - I know of a major architect who is now being sued because of their use of it in a 2006 slab. Our instructions removed the blotter layer in 1999. I look forward to getting deposed because it is not the Architect's fault. It is the structural engineer to whom they subbed out that work. I can't wait to throw him under the bus.

Even CalGreen (the new building code) still allows for it if the slab is "designed by a structural engineer". Well ... I can't wait to see one of these engineers get sued. They are the ones who are the cause in fact for 80% of the floor failures we have had to deal with. Not the flooring sub, not the gc, not the architect, not the curing compound, not the adhesive, not the material suppler, the engineer should be blamed.

It will be interesting to see what gets decided. But, it will probably settle out of court.

I disagree. Each sub inherits from the sub before him. If I put a floor on a wet slab, shame on me. If I put a rubber floor on a concrete slab with a blotter layer in strict disregard to the applicable ASTM's then shame on me!!! If the concrete sub sprays a sealer all over the slab and the installer goes over it and it fails, it's the installers fault!

[rthompson]

When a blotter is used, and there is a hole in the vapor retarder, the moisture will impact the entire slab. Example is a 16d nail hole in a vapor retarder will allow 3 pints of water through per day. That water will travel laterally in the blotter layer to affect the entire slab.
Curing compounds and sealers are a major concern to flooring installations. It is just one more thing to fail.
Rayt

[CC Solutions]

(04-09-2011 02:06 PM)rthompson Wrote:  When a blotter is used, and there is a hole in the vapor retarder, the moisture will impact the entire slab. Example is a 16d nail hole in a vapor retarder will allow 3 pints of water through per day. That water will travel laterally in the blotter layer to affect the entire slab.
Curing compounds and sealers are a major concern to flooring installations. It is just one more thing to fail.
Rayt

Curing compounds and sealers also limit the ability of the adhesive to absorb into the concrete and the ability of the moisture in the adhesive to dissipate and the adhesive to set. Adhesives between a moisture sensitive flooring and a sealed floor just won't set properly and are not approved.

[Ernesto]

I was reading this article and it has some interesting numbers for the water a granular blotter layer can hold.

http://www.stegoindustries.com/docs/WhereToPlaceTVR.pdf