# Help with vapor barrier had some mold growth



## gatorslayer18 (Apr 17, 2015)

I used rmax 1/2 and furring strips last year started measuring for cabinets and noticed surface mold on the unfinished drywall at the outlets and some screw holes. (Not black mold) I removed the drywall and noticed mold growing on the back side but only where the furring strips were touching the drywall. I replaced 90% of the wood when I replaced it couple years ago. Was i supposed to use a barrier? exterior wall,block home, stucco outside.


I plan on bleaching the wood (letting dry couple of days) then putting in the unfaced insulation and the 6mil plastic up, then drywall.

Would this be correct I live in FL.


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## joecaption (Nov 30, 2011)

No clue what Max 1/2 is.


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## gatorslayer18 (Apr 17, 2015)

Rigid foam board with foil backing


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## ThatDaveGuy (Dec 31, 2010)

Sounds like you might have leaking from the exterior that can't dry to the inside w/ the rmax up. My first though would be exterior flashing, sealing, etc., especially around any penetration like a window.


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## Windows on Wash (Aug 30, 2011)

+1

Sounds like warm and moist exterior air are leaking to the interior at the penetrations and condensing when they reach the cooler interior surfaces where the gaps and cracks are.


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## Gary in WA (Mar 11, 2009)

The furring is touching the colder drywall AND the warm CMU, without a impermeable barrier behind the wood (only)- on the block: you will always get condensation there. OR, exterior foam board (unfaced) to raise the condensing surface temperature. Block can warm itself from solar gain, the earth nearby, and warm air temperature.

NO FOIL-FACED; http://www.buildingscience.com/documents/insights/bsi-037-mold-in-alligator-alley

Gary


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## Yodaman (Mar 9, 2015)

gatorslayer18 said:


> then putting in the unfaced insulation and the 6mil plastic up, then drywall.
> 
> Would this be correct I live in FL.


This would be correct for a typical stick framed wall, but don't think this is correct for a CMU wall. I think the vapor barrier needs to go directly on the CMU, then furring, your unfaced foam, wall studs, w/ unfaced insulation. The cmu will wick moisture from the ground even if sealed well from the out side. Putting the VB under the drywall would allow the moisture to migrate into the fiberglass. 
Need a little more research and or input from insulation experts.


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## Yodaman (Mar 9, 2015)

Windows on Wash said:


> +1
> 
> Sounds like warm and moist exterior air are leaking to the interior at the penetrations and condensing when they reach the cooler interior surfaces where the gaps and cracks are.


Yes and if the house static air pressure is negative, it will pulll the moisture out of the cmu and into wall cavity. 

Under sized soffit vents caused a neg pressure situation in my own house. After it was corrected the inside RH went up 10 to 15%. Also my basement walls immediately dried, which always felt a little damp.


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## Yodaman (Mar 9, 2015)

Yodaman said:


> inside RH went up 10 to 15%.



MISSPOKE - This inside RH dropped by 10 -15 %, need more coffee :wink:


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