Using a non-PVA or vapor-open primer
We have done many basement remodels in the Portland, OR, area and have dealt with lots of different issues. The current dilemma (and fairly common) is that we have an old house that has no foundation waterproofing system. The basement is dry and has proper downspouts/rain drains and grading on the exterior.
A local building science guru recommended that we use a non-pva or vapor open primer to allow any humidity that diffuses through the concrete to dry to the inside. I could not find anything labeld a non-pva primer for the life of me. We talked to Sherwin Williams, Ben Moore, etc. and none of them had a drywall primer that was non-pva. Does anyone have a product that works for this??
Our wall assembly from the outside is as follows: wet dirt, 100 year old concrete foundation, 2″ unfaced EPS foam, 2×4 wall studs, R15 fiberglass batts, 1/2″ drywall.
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Just use a latex primer that isn't labeled "vapor barrier/retarder".
>"Our wall assembly from the outside is as follows: wet dirt, 100 year old concrete foundation, 2″ unfaced EPS foam, 2×4 wall studs, R15 fiberglass batts, 1/2″ drywall."
The vapor permeance of PVA primer with a couple coats of latex finish paint is about 3-5 perms.
The vapor permeance of 2" of Type-II EPS is less than 2 perms, roughly half the vapor permeance of the paint. Using a more vapor permeable non-PVA primer is not going to significantly change the moisture profile of the wall assembly.
Using EPS with a vapor barrier facer would basically eliminate the vapor diffusion of ground moisture into the studwalls, but may raise the moisture content of the foundation sill if there isn't adequate exterior above grade exposure on the foundation to allow ground moisture to dry toward the exterior. A foot is usually enough.
Thanks Dana,
Normally we used a faced EPS in our basement remodels and tape all the seams. In this case our new PM used an unfaced EPS because he found a deal on it, so that small permeability is what we are concerned about. I think if we still have 3-5 perms drying ability to the inside we should be fine?
What density is the EPS?
For foundation insulation applications it's usually Type II (1.5lbs per cubic foot nominal density), so that's the example I went with. If it's Type VIII (1.25lbs) roofing foam it could be as high as 1.8 perms @ 2" (which would still be fine), and if it's Type-I (1.0lbs) it could be as high as 2.5 perms, which is getting close to the vapor permeance of PVA primer. Type-I is usually sold with facers if only to make it more rugged in handling, but not always. If unfaced Type-I it's worth going with a higher permeance paint.
Weigh a sample to determine it's density if you're not sure.
I am not clear on why non-PVA as opposed to simply vapor open? Is there a concern this individual has with PVA in addition to the need for the paint to allow drying to the interior?
PVA stands for polyvinyl acetate and is a common component of most latex paints although you can get paints that pure acrylic; they are just typically more expensive.
Peter