I enjoy your “Wachuwannano ” articles every
month. Keep up the good work.
The question I have is, as a general contractor, when do I have
a right to tell finishers they are using too much water in their
joint compounds? And not only water, but everything from specialty mud conditioners to Joy and Ivory dish soap.
I personally do concrete, stucco and EIFS, and know excess
water can reduce strength more than 50 percent as well as
increase shrinkage. I have never had a job where six months later
you can’t see some joints. Sometimes it’s a couple of rooms, and
sometimes the whole job. As the home builder I always get the
blame from the finishers and also the distributors because I didn’t provide “satisfactory drying conditions.” Well nobody ever
complains when doing the work. I even pay for a “Level Five”
finish and specialty primers. I understand temperature and
humidity removal are important, but I keep thinking there
must be other causes. I have had crews put topping on with
paint rollers, which just seems too thin, (yes it was mud and not
primer). And with the pneumatic tools, compound seems to be
getting even thinner. I know the label says “a little water can be
added to improve workability” but how much is too much?? I
sure would appreciate your thoughts. —Byron J Anger
Glad to know you enjoy the column, it’s nice to know the work gets read.
I talked with a gypsum board manufacturer’s representative at
AWCI’s annual convention. His first suggestion was to get a
new drywall finisher. He was aware of the many concoctions
used by some finishers to supposedly enhance the workability
of mud. He strongly suggested reading the directions on the
bucket. Some of the newer lightweight compounds will turn to
soup if too much water is added, so you might want to include
a clause in your contract stating that manufacturer’s instructions
shall be followed.
ASTM C475, Standard for Joint Compound and Joint Tape for
Finishing Gypsum Board,has no physical property requirement
for viscosity. Mud manufacturers will generally produce their
products in a viscosity that is preferred by a specific market. For
example, a manufacturer may have one “flavor” or brand of
mud, but may have five different viscosity versions for five different market preferences. That said, ASTM C474, Standard
Test Methods for Joint Treatment Materials for Gypsum Board
Construction, does discuss viscosity only for consistency and
repeatability of testing for the physical properties required in
C475. The physical requirements for joint compounds in C475
are check cracking, putrefaction (spoiling)and shrinkage. Physical requirements for the Assembly of Taping or All-Purpose Compound and Joint Tape are bond and edge cracking.
Another avenue is to use the language in ASTM C840 for Level
5 finishes; at least this may help stop the roller action with mud.
22.6.6 Level 5:
22.6.6.1 All joints and interior angles shall have tape embedded in
joint compound and shall be immediately wiped with a joint knife
or trowel leaving a thin coating of joint compound over all joints
and interior angles. Two separate coats of joint compound shall be
applied over all flat joints.One separate coat of joint compound
shall be applied over interior angles. Fastener heads and accessories
shall be covered with three separate coats of joint compound.A thin
skim coat of joint compound shall be trowel-applied to the entire
surface. *Excess compound is immediately sheared off, leaving a film
of skim coating compound completely covering the paper. As an
alternate to a skim coat, a material manufactured especially for this
purpose shall be applied. The surface shall be smooth and free of toll
marks and ridges (see 22.4.1.1).
*emphasis added
About the Author
Donald E.Smith, CCS,is AWCI’s director of technical services.
Send your technical questions to him at smith@awci.org, or fax
them to (703)534-8307.
