Here are pictures of two buildings 150 miles apart, a home in Tahoe and a school in Tracy. Both were built years ago and both have the same delamination issue.

20150704_225503Both have the same trim, the same generic type of synthetic finish on top of a Portland Cement Plaster brown coat and the same moisture migration problem.

img_0003Give me your diagnosis of what has occurred and I will give you mine.

img_0009In both cases we have windows installed with the brown coat applied tight against the window jam and head. The wood trim was installed using nails penetrating the plaster, WRB and underlayment hopefully into the framing member.

The finish was applied to the edge of the trim creating a minimal seal of synthetic finish, and in other pictures of the school window/trim/finish joint, the finish and paint coat have been trashed.

The condition not seen but the most relevant is that bulk moisture on the face of the wall migrates off the finish except where the brown coat is not covered by finish, that would be around the windows under the wood trim.

That brown coat absorbs moisture aggressively. And moisture around windows can get into the body of the panel through the shrinkage crack between the window jams and the plaster.

When that moisture finds its way down the wall and cannot get out through the pores of the synthetic finish or elastomeric paint coat, the pressure of the water breaks the bond of the paint or finish coat from the brown coat to let the water out.

Part two I will talk about how we solved the problem on these two jobs and how to create details that will forestall the issue in the future.

If you have questions about this condition or other situations, call or email:

Bruce Bell
Bell Construction Consulting

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