RH Numbers Rising

[CC Solutions]

Think of concrete as waterproof! Swimming pools are made from it, dams, pilings.... You think the Hoover Dam is full of admixtures? (Maybe, I don't know ) but the point is concrete loves and needs water!

[Ernesto]

Did they even have admixtures when they built the damn dam?

So your saying elevated mve will not attempt to go up through the walls when a slab is covered with a 100% Moisture mitigation system? And no mold will grow on the wood framing? It has to go somewhere. Path of least resistance.

[CC Solutions]

What I'm saying is that moisture does not travel sideways through a slab.
Be sure you quote me as 'through' a slab. It can travel under a slab, through a blotter layer, run through cracks, flow across a slab, but it doesn't go sideways through a slab. So if you have a good vapor retarder under the slab, the area under a wall, in a HVAC chase, under a cabinet or whatever, will dry out over time while the rest of the slab covered by an impermeable membrane will stay wet.

Some have a hard time grasping this concept, but moisture locked in a slab is not a real problem. Really!!

[Ernesto]

Tain't nuthing under the cabinets or walls. lol

Quote:good vapor retarder under the slab

There is no definition of that in the southwest building codes...or least thats what the builders tell me. If you mention that you get a blank stare.

[CC Solutions]

I've done some work in the south and the west. It is so different than the Midwest!!!! Folks are a lot more laid back.... Real easy going and hospitable... And the southern gals Don't know how guys in the south can handle all those southern gals!

[rthompson]

Yes, The initial readings are generally lower due to the drying effect from thhe friction of the drill bit which creates haeat and drys the immediate area around the hole.This is why a period of time is required for the hole to equilibrate.
Rayt

[Ernesto]

I've tried to run my vacuum in the hole for a few minutes to cool it down. Not sure if it helps. But it seems like it should.

[CC Solutions]

(04-08-2011 08:01 AM)Ernesto Wrote:  I've tried to run my vacuum in the hole for a few minutes to cool it down. Not sure if it helps. But it seems like it should.

Maybe you should blow the hole out with compressed air. It is very cold and will clean the hole out.

[rthompson]

There is no doubt the hole needs to be thouroughly. With the vacuum you would pull in ambient air, which is normally drier than the concrete RH and that would tend to dry the hole further.
Rayt

[eaadams]

(04-06-2011 08:28 AM)CC Solutions Wrote:  It can travel under a slab, through a blotter layer, run through cracks, flow across a slab, but it doesn't go sideways through a slab. So if you have a good vapor retarder under the slab, the area under a wall, in a HVAC chase, under a cabinet or whatever, will dry out over time while the rest of the slab covered by an impermeable membrane will stay wet.

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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(04-05-2011 08:42 PM)Ernesto Wrote:  Well I got another annoying pertinent question. Whats a healthy rh percentage for a concrete slab? See where I am going? No, ok how about, where does all the mver's possibly h20 go when your slab is 99% and is only sealed around the perimeter of the walls. Does it go up into the walls?

Might not be a big deal in commercial apps but in a home, could lead to SHS. Can concrete stay 99% and keep it's strength and not deteriorate

Ernesto - yea it can get bad. Note your own referenced article @ Figure 1: Slab-on-Grade Done Right - http://www.buildingscience.com/documents...s/insights

(04-07-2011 06:12 AM)CC Solutions Wrote:  I've done some work in the south and the west. It is so different than the Midwest!!!! Folks are a lot more laid back.... Real easy going and hospitable... And the southern gals Don't know how guys in the south can handle all those southern gals!

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?