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Historic Preservation - Technical Procedures

Spectitle:

Removing Suspended Acoustical Ceiling System And Restoring Original Plaster Ceiling

Procedure code:

0951101R

Source:

Internet & National Capitol Region Specifications

Division:

Finishes

Section:

Suspended Acoustical Ceilings

Last Modified:

02/24/2012

Details:

Removing Suspended Acoustical Ceiling System And Restoring Original Plaster Ceiling



REMOVING SUSPENDED ACOUSTICAL CEILING SYSTEM AND RESTORING
ORIGINAL PLASTER CEILING


PART 1---GENERAL

1.01 SUMMARY

    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.

    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
         interiors.

    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

         3.   Submittals

         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).

1.02 REFERENCES

    A.   American Society for Testing and Materials (ASTM), 100
         Barr Drive, West Conshohocken, PA 19428, (610) 832-9585
         or FAX (610) 832-9555.

1.03 QUALITY ASSURANCE

    A.   Qualifications:

         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
              years.

         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
                   certificates.

              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
              manufacturer.

         2.   Take every precaution to allow plastered surfaces
              to cure properly without excessive heat or
              accelerated drying.


PART 2---PRODUCTS

2.01 MATERIALS

    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-
         28.

    D.   Finish Coat Plasters:

         1.   White gauging plaster, conforming with ASTM C-28,
              Type V.

         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.

2.02 MIXES

    A.   Proportions:

         1.   Parts, by weight, unless otherwise noted or
              directed.

         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.

    B.   Mixing:

         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
              are loaded.

         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
              discarded.  

         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-
              free putty.

         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.


PART 3---EXECUTION

3.01 EXAMINATION

    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
                   the building?  

              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
              treatments.

         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
              installation.

3.02 PREPARATION

    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
         concealed location.

    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.

    D.   Replastering:

         1.   General:

              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
              brown coat.

         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
                   plaster.

              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
                   as required.

              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
                   09200-11-R.

    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.

3.03 ADJUSTING/CLEANING

    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
         avoid scratching.

    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