So I'm in Minnesota, just buying a farm. One place I might use natural plaster is if I convert a certain pole building to be insulated and usable...I might use straw bale and plaster. Or something. But it gets way below zero here. (I guess I have to ask about the straw bale question too.) Will it be okay? Or where do I go to find out? (I'm also into free if possible - happy to use cattails and such. No source of the fancy sand, but there's ordinary sand here.
Natural plasters will work extremely well in cold climates on interior walls. I plastered the walls of my rammed earth tire and straw bale home in Colorado with earthen plasters. Straw bale will work well, too, so long as you do it right. Are you thinking about using earthen plasters on the exterior of the home? That could be problematic. You will need to protect the walls from driving rain. There are other ways of making earthen plasters more moisture resistant, as I outline in my book, The Natural Plaster Book. You might also consider lime-sand plaster on the exterior walls, but this takes a lot of experience and knowledge. I'd hire a professional if you want to go this route. That said, lime-sand plasters are really the absolute best finish for exterior walls in any climate that experiences significant rain.
I've heard of a lighthouse in Devon that survives due to centuries of regular maintenance with lime plaster over earthen walls.
Would more fiber in the plaster be a good tool for cold climates (less spalling due to freezing moisture)? I know that extra straw in exterior plasters seems to help reduce weather damage generally, and it might also add slightly more insulation value to the plasters.
(Of course, primary weather protection is even better, as it prevents water from wandering in there and freezing in the first place.)
The main thing with any natural building exterior finish is to give the whole building a more traditional look, with deep eaves and porches (this creates very short exposed upper walls, instead of tall surfaces that the weather can drive against below the eaves).
If you try to make a natural-finished house like the 1940's war-effort houses, or modern tract apartments with no eaves to speak of, you will be very disappointed in the performance. These types of unprotected exterior walls often have damp and mold problems with conventional materials too, but they're easier to hide and ignore with vinyl siding and stick-frame. You see similar problems in some of the freeform cob cottages; it's easy to make the roof too small for the thick walls, and create points where the eaves drip or splash directly onto the walls.
I'm P.O.'d about this right now because my mother's living in a townhouse with poor eave/wall proportions, and has been diagnosed with permanent respiratory problems (allergic asthma) that may be tied to episodes of mold in the walls and carpet when gutters were blocked. May just be living in a rainy climate, there's mold everywhere for months at a time. But I still don't like looking at the signs of water damage in her tall, exposed, 2-story walls with less than 12" eaves. Not just builders, but anyone choosing a place to rent or live, should know what good weather detailing looks like, and the signs of water damage that mark either ongoing problems or very careless remedies.
Thanks. I am thinking about inside walls. But the comments about exterior finish are interesting, because I'm dealing with a converted barn (cement block) which really needs some extra insulation. I'll inquire into lime-plaster. Looks like I need the book.
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