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

wrote:

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

Go to:

http://usg.com

Search for "back blocking" - they invented the technique so they can
explain it best.

Bob (but not THAT Bob) wrote:
wrote:

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

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.