USG IMPERIAL Basecoat Plaster - Manual

Preparation Protect the product from moisture during storage and on the job. In cold weather, heat the interior of the building to
a minimum of 55 °F (13 °C) for an adequate period before the application of plaster, while basecoat and finish is
being applied, and until the finish is dry. Air circulation should be kept at a minimum level during this period.
If possible, maintain building temperature-humidity combination in the “normal drying” area of the graph below.
When dry conditions exist, relative humidity often can be increased by wetting down the floor periodically. During
these periods, make every effort to reduce air movement by closing windows and deflecting heater blower and
duct output away from the surfaces being plastered. If the building temperature-humidity combination is in the
“rapid drying” area of the graph on page 2, or I
MPERIAL Brand Gypsum Base is applied over steel studs, special
joint treatment measures must be taken. These include the use of a S HEETROCK ® Brand 90 or 210 Setting-Type
Joint Compound (D URABOND ® ) or S HEETROCK ® Brand Lightweight Setting-Type Joint Compound (E ASY S AND ™ ) and
S HEETROCK ® Brand Joint Tape. Follow the directions below under “Joint Treatment” section of “Application.”
Application Mixing Mix plaster with a cage-type paddle driven by a heavy-duty drill capable of producing 900-1000 rpm minimum
under no load. Approximate water-plaster ratios for I
MPERIAL Brand Basecoat (hand or machine application) are
8 to 10 qt./80 lb. (7.5-9.5 L/36.3 kg) bag.
Place the water in a 12- to 15-gal. smooth-sided container. Start the mixer, slowly add plaster and mix at least
2 minutes to disperse lumps completely. Do not mix more than 5 minutes.
Joint Treatment For normal drying conditions—Apply I MPERIAL ® Brand Tape over all joints (edges and ends). Do not overlap tape at
intersections.
Align I MPERIAL ® Brand Type P (pressure sensitive) Tape over the joint and press it into place over the entire length
of the joint. Eliminate wrinkles and assure maximum adhesive bond by pressing the entire length of tape with a
steel finishing knife or trowel. Press the tape into corners with a corner tool. Do not overlap.
Alternatively, attach I MPERIAL ® Brand Type S Tape with spring-driven hand stapler using 3/8 Љ staples. Use two sta-
ples at each end of the tape; staple the remainder at staggered 24 Љ intervals. At wall-ceiling angles, staple
every 18 Љ to 24Љ along the ceiling edge only. For wall-to-wall interior angles, staple every 18Љ to 24Љ on one
edge only, working from top to bottom. Position the tape to bridge the joint at all interior corners without overlap-
ping. For fire-rated assemblies, staple either Type P or Type S Tape 8
Љ o.c.
S HEETROCK ® Brand Joint Treatment System When building temperature-humidity conditions fall in the “rapid drying”
area of the graph or I MPERIAL Brand Gypsum Base is applied over steel studs, use S HEETROCK ® Brand Joint Tape
embedded with S HEETROCK ® Brand D URABOND ® 90 or 210 Setting-Type Joint Compound or S HEETROCK ® Brand E ASY
S AND ™ Lightweight Setting-Type Joint Compound. Mix the compound in a clean 5-gal. container (plastic is
preferred). Use a commercial potato masher or a 1/2
Љ heavy duty 200- to 300-rpm electric drill with a drywall
blade-type mixing paddle. Drill speed must not exceed 400 rpm. Use the amount of water shown on the bag
and always sift the powder into the water to ensure complete wetting. Stir vigorously for 3 minutes; if lumps
remain, allow the mix to soak for a minute or two then restir until smooth.
Note: Do not contaminate compound
with other materials, dirty water or previously mixed batches. Do not retemper batches.
Butter joints with compound using a trowel or steel finishing knife to force compound into the joints. Center
S
HEETROCK Brand Joint Tape and press it into the fresh compound with trowel held at a 45° angle. Draw trowel
along joint with sufficient pressure to remove excess compound. After tape is embedded, apply a skim coat of
joint compound to reduce possibility of edge wrinkling or curing. Allow joint treatment to set and dry thoroughly
before plaster application. Plaster prefill is not required over S
HEETROCK Brand Setting-Type Joint Compound. Mix
and apply a finish coat, feathering 3 Љ to 4Љ beyond edges of tape. Allow to set before plastering.
I
MPERIAL
®
Brand
Basecoat Plaster
Application Tips
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