IMG_0549I was asked to go to a job in the Central Valley of California to look at come cracking. These pictures are 2 representative cracks that I found.

As you can see, there was crack control fabric applied on top of a brown coat, the picture on the left, and some aggressive movement created the chasm in the picture on the right. The finish was an acrylic with a medium dash finish texture and the aluminum reveal screed is one inch wide.

The problem occurred because the Architect wanted to create what he thought would be movement stress relief in the wall. He specified installing double studs and attaching the reveal screed on one stud. And then attaching the lath by laying the edge across the attachment flange of the trim but attaching the lath on the second stud. This created an “artificial plane of weakness” in the lath/trim attachment.

The principle could work, but two points need to be made. The edge of the lath should be nestled in the crotch of the trim, and both should be attached into a framing member.

He also thought the crack membrane would hold the Portland Cement brown coat together if there happened to be some stress at that point. There were no breaks in the reveals to allow for expansion or contraction, but manufactured junctions inserted where horizontal and vertical reveals met.

The structural steel and steel stud infill framing were installed with no thought to how much expanding steel elongates and what that stress does to plaster. The wall was put under stress and the plaster responded at it’s weakest point – the joint between the lath and the trim.

There are several ways of responding to expectations of structural movement, and they all have to be considered in the plaster panel as well as the framing.

If you’ve concerns about your plaster details and need some conversation, call or email:

Bruce Bell
Bell Construction Consulting

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