Paint choices
Hello,
We need to choose the paint for the interior walls in our Passive House, and I believe we were advised to use latex paint to introduce vapor retardation. We are in Pittsburgh, PA, Zone 5, with a lot of plants in the house, and a thick wall: exterior cladding, 1×4 rainscreen, 4” of mineral wool, Solitex Mento weather barrier, plywood, 6 or 8” of cellulose, 5/8” of drywall. Electrical outlets were sealed with electrical putty… On average, using Joe Listburek’s rule of thumb calculation for dew point, we pass, although it is still T.B.D. as to what our interior conditions will be like w/r to temperature and humidity. I read some of the blogs here on the topic, and understand vapor retarder Type III like latex paint would be sufficient to meet the code.
Looking through the paint options (need to be low VOC too), I have hard time finding any information about permeability, or even locate “latex” paint. Some latex content may be there, but the paint is called “acrylic”…? The manufacturers don’t seem to provide much info. Should one include some vapor-retarding primer instead? What products might be suitable to meet both criteria?
For low VOC, we determined these would meet the requirement.
• Per NGBS indoor air quality requirements, architectural coatings need to be selected from the following list: Sherwin-Williams Emerald (CARB), Sherwin-Williams Harmony (CARB, 2g/l), BEHR Premium Plus (meets GS-11 at 46g/l, but is not certified), Miller acro pure (certified GS-11, 6g/l), Benjamin Moore Natura (meets GS-11 at <5g/l, but not certified). Thanks, Lucy
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Replies
Yes, paint spec'ed as a vapor retarder is usually the primer. Sadly, most are relatively high VOC. My go-to source for mainstream relatiable high performance reasonably environmentally friendly paint is Ben Moore, but their vapor retarder primer is 99 g/L VOC.
This old thread might give you clues about where to look, even if the specs aren't up to date.
https://www.greenbuildingadvisor.com/community/forum/green-products-and-materials/20342/answers-moisture-vapor-retarder-primer-paints
A membrane is a way to accomplish the same function without VOCs. But it sounds like it's too late for that.
You might assume that from a human health perspective most of the VOCs from the primer especially will be gone by the time you move in.
Question: what electrical putty did you use, and was it in fact low VOC and not bad smelling?
I always find discussions of vapor retarder paint...curious. You can say that such and such a paint has a certain perm rating, but every time the house gets sold or rented to a new owner, another coat (or two) of paint goes on. Or the kids rooms get painted every couple of years with new schemes. All this makes the perm rating of the original paint (and wall assembly)...different. Right? Will decreased permeability due to multiple coats significantly diminish the ability of a wall to dry to the inside? Is this a robustness issue? I'm...curious.
Lucy, this is not especially germane to your question, but I can't help myself, I must tell a funny story about low VOC paint. (There is a lesson to it.)
Twenty years ago I built a high end corporate office and studio complex in midtown Manhattan. The architect was very environmentally oriented, and so he specified low VOC paint. This notion of low VOC paints, glues, carpets, furniture etc was quite new at that time.
About six months after we occupied the facility we started to notice that the walls didn't appear quite right. The tipping point was when an "anatomical" drawing slowly appeared on the wall of a rest room that the construction workers had used, kind of like a Virgin Mary sighting. Well this led to meetings with the GC, painting contractor, rep from the large paint manufacturer etc.
It turns out the painting contractor, a well known firm, had not primed the sheetrock per the architect's specifications, he merely applied two finish coats, and the low VOC paint didn't cover as well as the old fashioned stuff. Not using primer was ostensibly common practice in NYC office construction, they all claimed anyhow. What happened? Much topcoating etc, with smelly paint, in an occupied office complex. So much for the VOC avoidance.
Anyhow, the lesson is, make sure your painting contractor is on board with your choice and technique!
PS: We used Ben Moore Aura in our house, it was super. Probably doesn't make your VOC spec though.
Andrew,
The Achilles heel of many complex energy efficient assemblies will probably end up being future occupant behaviour. People expect to be able to do routine maintenance and make minor changes to their residences without suffering adverse consequences. To me, expecting them to refrain from using certain common interior finishes, like paints, tiles, mirrors or wall paper, does'n make for a very robust house.
Lucy,
The terms "latex paint" and "acrylic paint" are interchangeable. Either term is used to distinguish paints that require water for clean-up from the old-fashioned oil-based paints that required paint thinner for clean-up.
Almost no one uses oil-based paint anymore to paint interior drywall or plaster, so (for all intents and purposes), "latex paint" means "paint."
Malcolm,
You're right, of course, that occupant behavior often undermines the plans of designers and builders. (My favorite example is when a certain wall assembly works, but only if the occupants keep the interior RH below 30% during the winter. If the occupants turn off the bathroom exhaust fan and install a humidifier, the wall fails. Not good.)
But I don't think we have to worry too much about multiple layers of interior latex paint. I've talked to Joe Lstiburek and John Straube about this issue, and neither of them is particularly concerned. After all, the original purpose of the paint (from a building science perspective) is to make the interior surface of the wall a little less permeable than unpainted drywall. If you throw on four more coats of paint, the wall's performance won't shift into dangerous territory. It will just become a little less permeable. Assuming that the wall was built with attention to airtightness, it should still perform well.
Big interior mirrors glued to the wall are a different story, of course, especially in hot, humid climates that have months of air conditioning. It's a good idea to install mirrors on stand-offs (with a 1/2-inch air space between the mirror and the drywall) in those climates.
I used a potassium silicate paint on my new house (http://romabio.com/). It is absolutely zero VOC as far as my nose can tell. You won't be able to smell anything even if you stick your head into the pail. It is 90 percent vapor permeable. A little pricey but a wonderful product if you can stand the smell of latex or oil-based paints.
I am also trying to decide on paint and primer. Did you choose a brand? What brand primer did you end up using? I have used the bullseye 1-2-3 primer a lot in the past. Does anyone know if this is a good vapor retarding primer?
Kail,
Here is a link to the technical data sheet for Zinsser Bulls Eye 1-2-3 Water-Base Primer. It makes no claim to be a vapor-retarder paint -- so you should assume that it isn't.
I have had good luck with Benjamin Moore Aura and now Natura paints. Both are zero VOC and paint and primer in one. I started using Aura about 7 or 8 years ago and Natura about 3 years ago. Aura is listed as Acrylic and proprietary resins while Natura is listed as 100% acrylic latex. I could not find the perm ratings on either, but as 100% acrylic latex Natura should be fine for a class III VR. The only difference I noticed between the 2 paints were that: Aura covers a little better, smells a tad worse (though better than most paints) and costs more than Natura. Neither one is cheap, but they usually provide almost double the coverage of cheap paints.