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high RH readings after 5 months

#3
Jeff,

I'm also in the bay area. We have plenty of slabs still reading 99% like you speak. Just finished sealing a job in Eureka yesterday that had been enclosed for 6+ months and had no blotter barrier. I have another one starting in menlo park and everyone is puzzled why it is still sitting at 99%. (both of these jobs were done right with no blotter layer)

#1 and you should have a serious warning light on with this, the 2" blotter layer is against code now, (calgreen) so watch out. If you get a moisture problem, whoever did that blotter layer is highly liable in a construction defect claim & also the design team is in trouble in a design defect claim. The flooring person is liable for not pointing this out pre-construction as is the GC & Concrete Contractor. It is flooring 101 and guys are getting sued left and right about it up and down the state.

Certainly that 2" blotter layer is the issue. If you didn't get enclosed until december the slab was rained on, maybe once or twice in I think that odd rain we got in October. The rain came down and went right through your saw cuts & joints, straight down to the sand. That sand acts like a huge sponge & will feed that slab with moisture forever. That is just how it works & why the blotter layer is no longer allowed.

Jason has a good point about the 1.6", your test should have been at 1.6". However, I have to say I've often thought about this. The blotter layer is against ACI. ASTM assumes people follow ACI. I would be willing to bet that an accurate ASTM instruction for a slab with a blotter layer would have a deeper probe. Pure conjecture but I just suspect that the point of the RH is to test the 'future' moisture and the blotter layer is a huge source of 'future' moisture. So in the presence of a blotter layer a deeper probe would make sense. (I am just talking / thinking here, not meant to be relied on)

"sensor in the hole, capped and then put under dome"

what dome? I think IFTI did this didn't they?
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RE: high RH readings after 5 months - eaadams - 03-13-2014, 09:46 AM

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