This month’s question involves more than the actual finishing
of the joint and goes somewhat beyond the realm of the standard
but justifies a look at the industry information available.
The designer had specified that the gypsum panels be installed
perpendicular to the framing. While this works without problems
most of the time, when the length exceeds the standard
available manufactured lengths, a butt joint occurs. Butt joints
are difficult to finish, and a crown will occur even at the hand
of the most experienced finisher.
The real problem surfaced when the wall angle for the ceiling
grid was installed. The crown on the butt joint caused a gap
between the wall angle and the face of the drywall. The contractor
wanted to know if there were industry tolerances defined
to establish the acceptability of changes in surface levelness
much like the tolerances used for flatness of a concrete floor
slab. After research I could not locate definitive tolerances in
any of the standard for installing and finishing drywall. In one
book I did find the suggestion that hanging drywall panels perpendicular
to the framing produces fewer joints to finish and
thus a saving in labor occurs.
In most cases this method using the longest length of drywall
panels available in spaces with dimensions less than the longest
length panel would not produce butt joints and would in fact
require less labor in the finishing process. However, the case in
question had spaces far exceeding the longest lengths available.
Further research on finishing butt joints shows that butt joints
will produce a crown. This fact is recognized by United States
Gypsum Company and in their Centennial Edition of The
Gypsum Construction Handbook Earlier editions do not go
into the same depth of detail except to say that the “Finishing
coats of joint compound must be feathered wider (approx. 18
inches) than for edge joints because there is no taper in which
to embed tape.” The Centennial Edition states: “End Joints—
Because ends of gypsum panels are flat and have no taper like
panels edges, end joints are difficult to conceal. Also, exposed
paper on ends may cause visible ridging or beading. The following steps are recommended for joint treatment to minimize
crowning and/or ridging of end joints:
“1. Before attachment, bevel panel ends approx. 1/8” at a 45
degree angle using a sharp utility knife. This keeps the paper
ends apart and reduces expansion problems caused by the raw
paper edge. Also peel back and remove any loose paper.
“2. Gypsum panel ends should be loosely butted together.
Ends should be separated slightly and not touching.
“3. Prefill the recess with joint compound and allow to set or
dry.
“4. Apply compound and paper reinforcing tape over the joint
in the same manner as for tapered joints. Embed tape tightly to
minimize joint thickness but leave sufficient compound under
tape for continuous bond and blister prevention.
“5. Finish the end joint to a width at least twice the finish
width of a recessed edge joint. This will make the joint less
apparent after decoration as the crown will be more gradual.”
The conclusion to be taken from this is that USG recognizes
the need to treat butt joints differently and at the same time
acknowledges that a crown of some type and size will be part of
the finished product. The problem of using butt joints on the
project in question could have been resolved by requesting a
change to allow the gypsum panels to be hung parallel to the
framing. This would have increased the labor to finish the dry-wall
but would have eliminated butt joints and the resulting
crowning that was found to be objectionable.
About the Author
Donald E. Smith, CCS is AWCI’s director of technical services.
Send your questions to him in care of AWCI’s Construction
