I have two sheets of 4x12 by 2/2" 16" OC that will butt together end to end. Can somebody explain the technique where you put a thin spacer board on the rafters closest to the butt end to make the butt slope slightly towards the rafter to allow for easier mudding? What size should the spacers be and on what rafters are they placed? thanks
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Search for "back blocking" - they invented the technique so they can explain it best.
i haven't done it, but i have heard about the technique. you use two strips, probably 1/8 or slightly thicker, and apply them on the rafters on either side of the joint. this creates a low spot at the joint and makes finishing the butt joint easier. i think you need to make the strips a little wider than your sheet so it fits under the adjacent course.
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