USG IMPERIAL Finish Plasters - Manual (Page 4)

Treat joints of the fiber board panels using S HEETROCK Brand Joint Tape and a S HEETROCK Brand Setting-Type Joint
Compound (D URABOND or E ASY S AND ). Provide an additional coat of setting-type compound to fully conceal the tape.
Allow to completely dry. When the joints are completely dry, treat the entire wall surface with USG Plaster Bonder
according to the application directions. Then apply D
IAMOND Brand Veneer Basecoat Plaster 1/16 Љ to 3/32Љ thick
using scratch and double-back technique. This is accomplished by applying a tight, thin coat over the entire area,
and immediately doubling back with plaster from the same batch to achieve full thickness. When basecoat plaster
is firm, broom the surface to leave it rough and open for finish. With basecoat set and partially dry, apply I
MPERIAL
Brand Finish Plaster, using a scratch and double-back technique. Complete finishing when material is firm. Leave
finished surface smooth and dense for decorating.
Note that this two-coat technique also works for application over 5/8 Љ F
IBEROCK Brand Abuse Resistant Panels,
5/8 Љ I
MPERIAL Brand Gypsum Base, F IRECODE Core, or 1/2 Љ I
MPERIAL Brand Gypsum Base, F IRECODE C Core, in any fire-
rated design, as long as 20-gauge steel framing is used and the proper joint treatment procedure is followed.
Veneer Plaster Prior to application of Finish Plaster, the D UROCK Brand Cement Board must be treated with USG Plaster Bonder
Over D UROCK ® Brand and the joints treated with S HEETROCK ® Brand Joint Tape and S HEETROCK ® Brand Setting-Type Joint Compound
Cement Board
(D URABOND or E ASY S AND ). Then apply D IAMOND Brand Veneer Basecoat Plaster as a basecoat. With the basecoat
set and partially dry, apply I MPERIAL Brand finish plaster using a scratch and double-back technique. Complete the
finishing when the material is firm. Leave the finished surface smooth and dense for decorating. Note that only
two-coat veneer plaster system may be used over D
UROCK Brand Cement Board.
Veneer Plaster over sanded S TRUCTO -B ASE High-Strength Basecoat Plaster—You can achieve extraordinary levels
of indentation and impact resistance, as well as superior abrasion resistance with I MPERIAL Brand Finish Plaster
used as the finish coat in this system. Apply a base coat of D IAMOND Brand Finish Plaster. Allow the base coat to set
and leave it rough to provide proper suction for the finish coat. Apply a finish coat of I MPERIAL Brand Finish Plaster as
indicated above.
Finish Plaster When applying finish plaster to I MPERIAL Brand Gypsum Base, the paper on the gypsum base should be blue.
to Degraded Sometimes plastering on a jobsite can’t be done until long after the gypsum base has been installed and there
I MPERIAL Brand
has been lengthy exposure to ultraviolet radiation from sunlight. When gypsum base has become degraded due
Gypsum Base
to exposure to sunlight, the face paper turns from blue or grayish blue to gray or tan. When the face paper color
becomes gray to tan, it must be treated with USG
™ Accelerator—Alum Catalyst.
For Alum Catalyst treatment, dissolve three lbs. of alum in one gallon of water. Pour the alum slowly into water and
mix thoroughly. Allow the solution to stand until any undissolved materials have settled; then strain the solution into
a tank-type sprayer (such as a lawn and garden sprayer). One gallon of solution should treat 750 sq. ft. of gypsum
base. Begin applying finish plaster before the alum solution is completely dry.
Note: Alum treatment reduces the
setting time of Diamond Brand Interior Finish Plaster. Note: If USG Accelerator—Alum Catalyst is not available, an
alternative solution is to apply USG ™ Plaster Bonder over the faded Imperial Brand Gypsum Base. Note: Using USG
Plaster Bonder to correct degraded gypsum base will require you to use a two-coat veneer plaster system, since
the bonder application will eliminate base suction needed for proper one-coat veneer application.
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