New stucco over foam: cementitious or synthetic color coat?
My New Mexico house is getting a whole new stucco job and the new stucco is over 1.5 inches of EPS insulation, making the wall sandwich look like this outside to in:
Cementitious stucco w/ metal lath
1.5″ unfaced EPS foam
0.25″ cementitious stucco
Latex paint (ugh)
0.75″ cementitious stucco
Single layer of tar paper
2×4 stud wall insulated with faced mineral wool batts
The cementitious base coat is on, and now I get to choose what kind of color coat to put on: cementitious or synthetic. I was all set to choose cementitious, but in the two weeks since the base coat has gone on, it’s developed a bunch of tiny cracks all over, and some slightly longer straight ones at the joints between the foam boards. None are big. The base coat was fiber-reinforced, so I suspect that some of the cracks are the result of the foam expanding and contracting, and maybe the low temperature?
So now I’m questioning the wisdom of applying a cementitious color coat if it’s just gonna immediately crack as well. My neighbor has a synthetic color coat on his house and there are zero cracks after 6 years.
Is there any reason I should be concerned about a synthetic color coat? I worry that it could trap moisture, but I live in the desert and there’s foam under it…
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