Most of the time, I use ready-mix joint compounds to tape and
finish the drywall I hang. But occasionally I find myself
working in less-than-ideal drying conditions, or on small jobs
that need to be finished within a day or two. To keep these
jobs moving, I reach for bags of setting compound instead of
buckets of mud.
Setting compounds harden through a chemical reaction rather
than through evaporation, making their setting times
predictable and consistent. And once a coat of setting compound
has set up, it can be covered with another layer of compound
even if it's not completely dry, which speeds along the taping
In addition to using setting compounds on small jobs that I
need to finish as quickly as possible — and on most of my
repairs — I use them to prefill gaps or damaged areas
before embedding tape.
Types of Compounds
While opening a bucket of mud is easier than mixing up a batch
of setting compound, drying-type compounds (conventional
premixed muds) can be tricky to work with. They perform best
when the air, the compound, and the surface are all the same
temperature — before, during, and after taping. They
require a minimum temperature of 55°F; their drying time is
greatly affected by temperature, humidity, and airflow. In
fact, if conditions remain poor after taping is complete, it
could take weeks for the mud to thoroughly dry.
Advantages of setting compounds. Setting compounds are more
forgiving than their drying-type counterparts, so they offer
better results under a wider variety of conditions. They can be
used in temperatures as low as 45°F, and will set even in
extreme humidity. They offer rapid hardening, low shrinkage,
and an exceptional bond that is virtually unaffected by climate
Keep in mind, though, that while setting compounds can be used
even in low heat and high humidity conditions, quality drywall
work still requires proper temperature, humidity, and airflow.
Otherwise, cracking and ridging can occur as temperature and
humidity levels normalize when the building is occupied.
Also, setting compounds shouldn't be applied over moist, dusty,
or cold surfaces. The same goes for very dry surfaces, because
the moisture in the compound may be drawn out too fast,
resulting in a poor bond.
Brands. Most lumberyards and paint-supply stores carry
one or two varieties of setting compounds (see Figure 1). I
haven't noticed any significant differences between brands, so
I use what is available in my area — primarily Sheetrock
Durabond and Easy Sand (800/874-4968, www.usg.com).
Figure 1. Though not as hard or as strong
as regular setting compounds (at left), lightweight setting
compounds (at right) are sandable and almost as easy to finish
as premixed joint compounds.
Setting time. Setting compounds come with different
setting times. Five-minute compounds are great for quick
patches, whereas 300-minute ones are perfect for overnight
drying. I stock 20-minute, 45-minute, and 90-minute compounds,
but use the 90-minute kind the most.
Sanding. Setting compounds also come in nonsandable
and sandable versions. I use Durabond — a nonsandable
compound — for heavier fills and in places where extra
strength is needed, such as corner beads in heavy-traffic areas
(Figure 2) and off-angle inside corners on sloped
Figure 2. Setting compounds are ideal for
repairing damage and filling large cracks before taping (top).
Because of its exceptional bond strength, the author often uses
setting compound when installing corner beads, which are
subject to daily impacts, and when using fiberglass mesh tape,
which is weaker than paper tape (bottom).
Lightweight (sandable) setting compounds like Easy Sand aren't
as strong as the nonsandable types, but they can be sanded
almost as easily as drying compounds.
Despite their forgiving nature, setting compounds do need to be
properly mixed. The temperature and quality of the water and
the way in which the ingredients are mixed can affect the
quality of the final product and its actual setting time.
Water temperature. Using cold water can result in a chunky mix,
and can also slow the setting time. I've found that simply
allowing the mixed compound to slake a few minutes longer than
normal minimizes this problem.
Using hot water, on the other hand, decreases the setting time
and can result in wasted material. A 45-minute compound, for
instance, can set in as little as 35 minutes when it's been
mixed with hot water.
Compound temperature. One of the benefits of powdered
mixtures is that they don't have to be protected from freezing
temperatures. Nevertheless, for best results the bags should be
brought to room temperature before mixing; if the powdered
compound is too cold you could end up with a lumpy mixture, and
if it's too warm the mix may cure too quickly.
Clean vs. dirty water. The quality and setting time of
the mix — and the strength and bonding abilities of the
final product — are always better when clean water is
used. However, I've experimented with using the dirty water
left over from cleaning mixing tools and empty buckets, and to
my surprise, the resulting mix seemed very usable. Just the
same, I don't really recommend this approach if clean water is
readily available, because it might make a five-minute or
20-minute compound set too quickly to use; I'd also be
concerned about the compound's strength.
A more important issue when mixing is to avoid using dirty
tools coated with setting compound, or buckets that still
contain a thin layer of the stuff; these conditions have the
biggest effect on setting time. Whether you're using 90-minute,
45-minute, or 20-minute compound, it'll start to set up early
if you use a coated tool or bucket. So always clean up as soon
as you finish mixing a batch: Scrub your tools and the inside
of the bucket and rinse with clean water. Merely setting your
mixing paddle in a bucket of water won't prevent the compound
from setting up.
Add the compound to the water. Starting with clean water in a
clean bucket or mud pan, I add a little compound at a time as I
mix. Once it's reached the desired consistency — that of
premixed mud — I wait a few minutes to let the compound
slake and to give chunks time to dissolve. Then I mix it again
— just as I would do if I were mixing tile grout.
I use a mixing paddle for large batches, typically a single
blade or cage-type paddle, which makes cleanup easier. For
small batches, I use a cake mixer installed in a drill; it
gives me a quick and creamy mix (Figure 3).
Figure 3. The author uses a mixing paddle
for large batches (left) and a cake mixer mounted in a cordless
drill for smaller ones (right). To avoid lumps and
unpredictable results, he makes sure the water, tools, and
containers are clean, and pours in the water first, then the
For heavy fills, the compound can be mixed thicker so it won't
sag or run. Start thin, then add a little compound at a time to
thicken the mix. Just make sure it's thoroughly mixed, and be
aware that thicker mixes tend to set up a little faster.
When embedding tape, I use a thinner mix (according to USG,
setting compounds can be mixed quite thin without compromising
strength). Setting compounds are usually used for hand taping,
so there's little need for the kind of extra-thin mix that
would be used with production taping equipment.
Working With Compounds
The amount of compound I mix is based on the setting time and
the size of the job. When taping a single room, for example, I
may estimate that it will take 90 minutes to apply the taping
coat. On a job like this, I typically want to be able to apply
multiple coats of compound with as little time between layers
as possible. But instead of using a 90-minute compound, I'll
mix up two or three small batches of the 45-minute material.
That way, I can minimize waste and increase the likelihood that
I'll able to apply the next coat as soon as I finish.
If I have only the 90-minute compound with me and the job is
small enough to coat in less time than that, I'll mix the
compound early. I may mix it up before I finish hanging the
drywall, or before cleaning or doing other prep work.
It's important to remember, though, that once the compound
starts to set up, it cannot be remixed.
In general, I try to apply compound in thin, even coats with
nicely feathered edges. This is especially critical because
regular setting compounds are virtually impossible to sand
Figure 4. Since regular setting compounds
can't be sanded, the author applies them in thin coats and
feathers the edges (top). After the compound has set up (but
before it's dry), tool marks and ridges can be shaved off with
a sharp taping knife (bottom).
When I tape with a drying compound, I lightly sand before
applying the finish coats, which removes tool marks and
unfeathered edges and leaves a smooth finish. But sometimes I
want to apply a second coat before the first coat is dry; in
those cases — since a setting compound can't be sanded
while it's wet — I use the sharp edge of a taping knife
to shave off any uneven surfaces on the set-up (but still wet)
For the finish coat, I use a drying compound, which is lot
easier to work with when you're doing very thin top coats. No
time is really lost, because in order to finish-sand and then
decorate, all layers of compound have to be thoroughly dry
Drying compounds can be applied over setting compounds and vice
versa; just be aware that different compounds sand differently.
If you're finish-coating with a lightweight drying compound
over a setting compound, you'll need to be extra careful when
sanding; the softer drying compound will sand away easier than
the setting compound, leaving an uneven finish —
especially if you're using too soft a sander. And before
finishing and decorating, all layers of the compound must be
Myron Ferguson is a drywall contractor in
Galway, N.Y., and moderator of the JLC Online drywall