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How to protect an exterior clay based plaster wall from the humidity of an attached greenhouse

Posts: 80
Location: Manitoulin Island - in the middle of Lake Huron .Mindemoya,Ontario- Canadian zone 5
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I have a timber framed strawbale house 2/3 constructed. The walls are all up and plastered inside and out with a clay based ( also contains some sand and finely chopped straw) plaster. The plaster was painted with a couple of coats of Eco-House house white silicate dispersion paint.

One of the next steps in construction is to build the attached southern greenhouse, which already has a concrete block foundation in place. I would have preferred earth bags, but the learning curve for me and my builder was just too steep, so we went with concrete blocks. There will be large, raised growing beds along the northern wall of the greenhouse, which is also the southern wall of the house proper. There are steps down from the main floor ( 4 ft above grade) to the ground level walkway of the green house. The highest point of the greenhouse roof will attach to the house wall at the level where the the first and second floors meet, then the roof slopes down to the south vertical wall of the greenhouse.

I am wondering about moisture and mold possibly affecting the exterior surface of the house's southern wall. There is blue-skin covering the concrete blocks of the foundation and knee wall up to about 4 feet above grade, and the soil in the growing beds will be in contact with this. Directly above the concrete, however is the painted earthern plaster. Greenhouses are damp, splashing can occur during watering and damp plants can grow and touch the wall - should I worry about the earthen plaster near the grow beds? Should I coat that area with something less breathable than the Eco-House silicate paint? Or is the paint enough?

Thanks for any advise you can give me on this.

Manitoulin Mary
Posts: 2413
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Hi Mary,

You seem to have a lot of "moving parts" here that you are needing to work in concert with each other. With the type of build you have started with SB and then OPC block imagination, I really would need to see pictures of what you have so far to give any type of advice. The paint you chose is a great one, with a long history. I would suggest you could have done just as well with a traditional lime paint at a fraction of the price. Until I see pictures (and probably after) I have more questions than answers at this point. Attached greenhouses are wonderful, and I am currently designing one into a small home for a client...they do take a great deal of planning and forethought.


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