Applying Vapor Barrier Primer
I am in zone 5 in Salt Lake City, Utah. “Pretty Good House” 4000 ft2 with a roughed in ACH50 result of 1.01, double stud walls, and rain screen.
We specified using a vapor barrier primer from Sherwin-Williams. We are getting ready to start painting drywall next week and my contractor is concerned about the quality control of applying this product and also the cost. Standard primer is $19/100ft2 and moisture barrier primer is $38/ft2.
A few questions:
1) Applying the vapor barrier primer at 6-8 mils, compared to 4 mils for standard primer is concerning per my general contractor. He is not sure how to manage quality control since this is not typical for his painters. We thought of marking off 1100ft2 areas on the floor to ensure it is being applied thick enough. Any other ideas? Should we just measure wet mils with those card gauges as a calibration?
2) We are considering using normal primer on interior walls and The Moisture Barrier Primer on the exterior facing walls and ceiling. Do I have to worry about vapor diffusion migrating from the interior walls to the exterior? This method might be confusing but will save ~$800 in primer. I’m not too concerned about $800 but I don’t want to through away money if it is an option.
3) Another thought we had was apply the Moisture Barrier Primer at the painter’s normal application rate of 5gal/400ft (4 mils). Then go back and apply a second coat on the exterior walls and ceiling to our required DFT.
In short, how do I ensure I get the right thickness of primer with painters used to applying a different product that needs to be applied twice as thick?
Thanks for the help.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Use a wet Mill gauge (the card thing) ask S&W for the wet mill thickness and dry mill thickness.
All the painter has to do is roll a section check it with the wet mill gauge. My guys do that every day. If you want to double check it, pick up a cheep micrometer scrape off a small pice and measure it, one mill = one thousandth of a inch.
If there's a air vapor barrier under the veneer, I would be careful with the vapor mitigating primer.
You could loose your perm rating.
If you use it on exterior side of exterior wall I would not put it on interior side of same wall and defiantly not on interior walls.
You're not in a humid area like Florida so I don't understand why you're using vapor mitigating
primer. You do realize the paint is a vapor mitigator , if you're worried about vapor drive add a few more mills of paint.
What most people don't understand is to have a true Air vapor barrier all walls ceiling and floor to exterior have to be coated (Think of it like painting a cube) that's from AABA American Air Barrier Association.
utah_matt,
What level of perm are you trying to get down to? Vapour-retarder primer yields somewhere in the 0.45 to 0.9 range. Two coats of regular latex will be about 5.
The paint is the primary vapor barrier so we are trying to get a class II, less than 1 perm.
utah_matt,
I would lean towards option three if it isn't too expensive. My fear is that one thick coat may have a poor finish quality, but maybe that concern is misplaced?
You don't need VB on the interior walls, just exterior.
Just to make sure everyone is reading this thread correctly:
'Interior' walls refers to interior partition walls—not the interior face of the exterior walls. Exterior walls implies walls that separate the indoors from the outdoors—exterior is not referring to the exterior face of the wall. The vapor retarder is being used on the interior face of the exterior walls.