Historic Preservation - Technical Procedures
- Removing Suspended Acoustical Ceiling System And Restoring Original Plaster Ceiling
- Procedure code:
- National Capitol Region Specifications
- Suspended Acoustical Ceilings
- Last Modified:
- Removing Suspended Acoustical Ceiling System And Restoring Original Plaster Ceiling
- Last Modified:
REMOVING SUSPENDED ACOUSTICAL CEILING SYSTEM AND RESTORING
ORIGINAL PLASTER CEILING
A. This procedure includes guidance on removing a suspended
acoustical ceiling system to restore the original plaster
ceiling above. This may include duplication of various
ornamental plaster features as required to replace
damaged or missing elements. THIS WORK SHOULD BE
PERFORMED BY AN EXPERIENCED CONTRACTOR SPECIALIZING
IN HISTORIC PLASTERING TECHNIQUES.
B. The installation of suspended acoustical ceiling systems
in GSA buildings often results from the necessity to
conceal new ductwork for mechanical and/or fire safety
systems, or to reduce energy costs for heating and
cooling. As a result, the character of original spaces
is often compromised. In some cases, highly detailed and
decorative plasterwork is obscured and often damaged in
order to meet these needs.
C. Depending on the function and location of the space, the
significance of the obscured ceiling, and the purpose for
installing the suspended ceiling system, removal of the
system and restoration of the original plaster ceiling is
recommended when feasible, particularly in areas of
significance. See 01100-03-S and 01091-20-S for
recommended approaches in rehabilitating historic
D. For guidance in planning for the installation of new
mechanical, electrical or fire safety systems in historic
buildings, see 15010-01-S, 15010-03-S and 15300-01-S.
E. See 01100-07-S for general project guidelines to be
reviewed along with this procedure. These guidelines
cover the following sections:
1. Safety Precautions
2. Historic Structures Precautions
4. Quality Assurance
5. Delivery, Storage and Handling
6. Project/Site Conditions
7. Sequencing and Scheduling
8. General Protection (Surface and Surrounding)
These guidelines should be reviewed prior to performing
this procedure and should be followed, when applicable,
along with recommendations from the Regional Historic
Preservation Officer (RHPO).
A. American Society for Testing and Materials (ASTM), www.astm.org .
1.03 QUALITY ASSURANCE
1. The reproduction, manufacture and installation of
the decorative plaster moldings, brackets, dentils,
leaves, scrolls, cornices, and all other ornamental
plaster shall be executed by a firm who has
executed work on other projects equal in scope to
this project for a period of not less than seven
2. Submit list of projects and before and after
photographs to demonstrate the firm's capability.
1.04 DELIVERY, STORAGE AND HANDLING
1. Packing and Shipping:
a. Deliver materials to the job site, ready for
use in the manufacturer's original and
unopened containers and packaging, bearing
labels as to type and material, brand name,
and manufacturer's name. Delivered materials
shall be identical to reviewed samples and
b. Deliver shop cast ornamental decorative
plaster to job site properly protected and in
lengths and shapes as required.
2. Storage and Protection: Store materials under cover
in a dry and clean location, off the ground.
Remove materials which are damaged or otherwise not
suitable for installation from the job site and
replace with acceptable materials. Protect plaster
and all cementitious material from intrusion of
dampness and foreign materials.
1.05 PROJECT/SITE CONDITIONS
A. Environmental Requirements:
1. Maintain a uniform temperature of not less than 55
degrees F. in areas of spaces to receive plaster
finish. Maintain temperature a week before, during
and after installation. Distribute heat uniformly
with proper ventilation recommended by the
2. Take every precaution to allow plastered surfaces
to cure properly without excessive heat or
A. Plaster Aggregate: Sand for interior plaster shall
conform to ASTM C-35.
B. Water: Potable and containing no impurities that will
affect the set of the plaster.
C. Base Coat Plasters: Gypsum plaster, regular with sand
aggregate for hand application, shall conform to ASTM C-
D. Finish Coat Plasters:
1. White gauging plaster, conforming with ASTM C-28,
2. Finish lime, conforming with ASTM C-206, Type S.
3. Hydrated lime, conforming with ASTM C-6, Type N.
4. Quicklime, conforming with ASTM C-5, Type B.
E. Molding plaster, conforming with ASTM C-28, Type V.
F. Materials, means and methods to reproduce the existing
decorative plaster shall be as recommended by the
specialty contractor for this portion of the work.
1. Parts, by weight, unless otherwise noted or
2. Gypsum plaster on masonry substrate:
c. First coat: 1 part gypsum plaster to not more
than 3 parts sand, by weight. Add fiber as
per reference standard.
d. Second coat: 1 part gypsum neat plaster to not
more than 3 parts sand, by weight.
e. Third coat: 4 parts lime putty to 1 part
gauging plaster, by volume.
3. Molding plaster: Mixture and proportions as
recommended by the specialty contractor with lime
putty to add plasticity and to act as a lubricant
for the template or cast.
1. Mix plaster in a batch type mixer at the
construction site. Frozen, caked or lumpy material
shall not be used. Clean mixer of all set or
hardened material before materials for a new batch
2. Mix each batch of plaster separately. Thoroughly
mix to obtain uniformity of color and workable
consistency of mass, and only in such quantities as
will be used before it has started to set.
Retempering after the plaster has started to set
will not be permitted and such plaster shall be
3. Mix hydrated lime with amount of water called for
in printed directions of the manufacturer. Treat
hydrated lime in a manner to obtain smooth or lump-
4. Slake pulverized quicklime by sifting it into
amount of water called for in printed directions of
the manufacturer and allow to stand 5 or 6 days or
until thoroughly slaked and allow to cool.
5. Batches for base coats must not be in excess of an
amount that can be entirely used within two hours,
and for finishing coats that can be entirely used
within thirty minutes.
A. Verification of Conditions:
1. Examine conditions above ceiling system to
determine whether removal and restoration is a
feasible task. Reference original or early
photographs and drawings to confirm original design
and detailing of spaces.
a. Does the system conceal extensive ductwork for
b. Is the obscured ceiling located in a
significant public area?
c. Are the obscured features ornamental,
decorative or otherwise significant?
d. What condition are the features in and what
level of effort would be required to restore
them if the suspended ceiling were removed?
2. Examine all existing plaster conditions. Restoring
the ceiling to its original condition may require
duplication of existing ornamental plaster running
moldings, cornices, ornaments, brackets, scrolls,
leaves, dentils, etc. (see 09200-05-R and 09200-11-
R for guidance). If duplication is not required,
the work may include replacement, repair or
restoration of work in place and to remain, to
produce whole continuous plaster surfaces and
3. Verify, by measurements taken at the job site,
those dimensions affecting the work. Bring field
dimensions which are at variance to the attention
of the Contracting officer. Obtain decision
regarding corrective measures before the start of
A. Protection: Cover floor with newspapers or dropcloths.
Protect carpeted areas with waterproof drop cloths.
3.03 ERECTION, INSTALLATION, APPLICATION
NOTE: CONSULT WITH RHPO BEFORE PERFORMING ANY KIND OF
DESTRUCTION/REMOVAL OF MATERIALS OR SYSTEMS THAT IMPACT
HISTORIC FINISHES. CONSULT RHPO TO DETERMINE FEASIBILITY AND
BEST MEANS OF REMOVAL TO AVOID DAMAGING SIGNIFICANT MATERIALS.
A. Remove ceiling tiles from structure; carefully remove
suspended ceiling structure, fasteners and other related
accessories. Take special care not to cause additional
damage to original plaster ceiling and ornament when
removing structure from the ceiling surface.
B. Remove exposed electrical installations and install in a
C. Carefully remove all soft, broken or loose plaster back
to masonry, lath and to solid adjacent plaster, making
clear and sharp edges; bevel inward. Sweep masonry and
laths clean and prewet surfaces.
a. Mix plastering materials and apply in strict
accordance with the manufacturer's published
specifications. Use materials without
admixture of materials other than those
specified herein in each instance. No
retempering or retarding of partially set
plaster mixes will be permitted, trade custom
or local practices notwithstanding.
b. Execute plastering in such a manner so that
the finished work will be free from
depressions, bulges, slick spots, scratches,
brush and tool marks, cracks, visible joints,
crazing and discoloration. Surfaces shall
have true planes, with uniform texture, and
with lines and arises that are straight, plumb
and level. Work shall be true to grounds and
guidelines and free from blemishes and defects
of any sort.
2. Apply base coat (scratch coat) of plaster. Apply
with sufficient materials and pressure to force
plaster to form good bond and cover well. Roughen
this coat to create key for finish coats. Allow to
set and thoroughly dry out before applying the
3. Apply second coat (brown coat). Do not apply brown
coat sooner than 48 hours after application of
scratch coat. Evenly dampen scratch coat to
provide uniform suction before brown coat is
applied. Thickness of brown coat shall be
approximately 3/8". Bring brown coat out to ground
and required lines, to true, even surfaces.
Straighten with rod and darby and leave rough to
accept finish coat. Moist cure brown coat for 48
hours after application, and then allow coat to set
and dry out.
4. Lap joints in scratch and brown coats including
joints at interior angles, continue past the angle
or corner and feather off on the adjacent wall.
5. Before the application of the finish coat, cut out
shrinkage cracks and fill with scratch coat mortar.
6. Apply finish coat well ground to scratched
surfaces, then double back, and trowel down,
filling all imperfections. Finish 1/16" to 1/8"
thick and treat and finish as directed.
6. Sand smooth troweled finishes lightly to remove
trowel marks and arises.
7. Finished Surfaces: Plumb, straight, level and true
throughout and shall not vary from a true plane by
more than 1/8" when tested with a 10 foot
straightedge at any point.
8. See 09200-03-R and 09215-01-R for additional
guidance in plastering.
E. Neatly repair or replace any damaged plaster cornices and
moldings to exact profiles, true with adjoining work,
keying the new work to the sound work in place.
1. For Patching:
a. Do all cutting, patching, repairing and
pointing of plaster work after other work is
in place, and at such times as directed.
b. Execute pointing around fixtures, outlet
boxes, switches, plates, fitting, piping,
conduit, registers, frames and other
appliances abutting or extending through the
c. Discolored, broken and damaged portions of
plaster shall be cleaned, cut out and filled;
repair work thoroughly and neatly. Cracks and
indentations shall be raked out or cut out,
moistened and filled with finishing materials.
d. Patched area shall match adjoining work in
texture and finish.
e. For patching existing work, cut back to sound
plaster on straight lines and back bevel edges
to remaining plaster. Provide new accessories
f. Provide plaster repair for ornamental work
which is not scheduled for complete
replacement. Execute work using skilled
workmen trained in this phase of the work.
Repair and restore cracks, chips, spalls, and
other damaged surfaces, and restore surfaces
and appearances to their original state.
g. For additional guidance in making plaster
repairs and replastering, see 09200-01-S,
09210-02-R, 09210-04-R and 09210-05-R.
2. For Replacement:
a. General: The Contracting Officer along with
the specialty Contractor will select portions
or whole elements, from which negative on-site
molds shall be made. The means and methods
for making these molds shall be solely in the
hands of the specialty Contractor, but whose
results shall be an exact duplication (less
flaws of existing) of the original in factory-
cast plaster complete with embedded and
integral means for securing the work in place.
The finished precast plaster work shall be
made from the field cast molds and delivered
to the job site ready for installation.
b. Prior to installation, accurately cut out
existing portions which are to receive new
precast plaster replacements. Provide
additional furring, lathing and supporting
elements for attachment of the precast
elements. Install into the existing work
maintaining perfect continuity of line and
design without break in pattern or appearance.
Set rigid, plumb, and secure in a concealed
manner. Double wire tie all connections.
c. Butter joints between precast and precast, and
between precast and existing, so that they are
not visible to the eye.
d. Installed and completed installation shall not
give the appearance that repair or restoration
work has been performed, and be acceptable to
the Contracting Officer.
e. For additional guidance, see 09200-05-R and
F. Clean plaster surfaces and remove loose paint. See
09200-08-R, 09900-07-S and 09900-08-S for guidance.
1. Plaster on lath may not be painted until one month
after it is installed if the room temperature is
kept above 50 degrees F. and the relative humidity
is kept below 70%.
2. Plaster on solid masonry backing may not be painted
until two months after it is installed with the
same restrictions as for the plaster on lath.
A. Exercise care to avoid soiling or spattering the plaster
onto the work of other trades. Use cover cloths or other
suitable means of protection. Should soiling or
spattering occur, remove it by sponging, brush cleaning
and as otherwise required before the plaster sets, to
B. Mop floors clean of refuse and debris. Take precautions
to prevent unnecessary staining and smearing of floors.
C. Protect finished plaster work against damage, and from
freezing or premature drying out.
D. Marking or writing on finished plaster surfaces will not
be permitted. The Contractor shall strictly enforce
observance of this requirement.
E. Protect plaster repair areas against too rapid drying,
based on manufacturer's instructions.
END OF SECTION