Removing Suspended Acoustical Ceiling System And Restoring Original Plaster Ceiling

PART 1—GENERAL

1.01 SUMMARY

1. 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.
2. 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.
3. 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.
4. 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.
5. 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

1. American Society for Testing and Materials (ASTM), www.astm.org.

1.03 QUALITY ASSURANCE

1. 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:
   1. 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.
   2. 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

1. 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

1. Plaster Aggregate: Sand for interior plaster shall conform to ASTM C-35.
2. Water: Potable and containing no impurities that will affect the set of the plaster.
3. Base Coat Plasters: Gypsum plaster, regular with sand aggregate for hand application, shall conform to ASTM C-28.
4. 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.
5. Molding plaster, conforming with ASTM C-28, Type V.
6. 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

1. Proportions:
   1. Parts, by weight, unless otherwise noted or directed.
   2. Gypsum plaster on masonry substrate:
      1. First coat: 1 part gypsum plaster to not more than 3 parts sand, by weight. Add fiber as per reference standard.
      2. Second coat: 1 part gypsum neat plaster to not more than 3 parts sand, by weight.
      3. 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.
2. 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. Re-tempering 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 the manufacturer and called for in printed directions 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

1. 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.
      1. Does the system conceal extensive ductwork for the building?
      2. Is the obscured ceiling located in a significant public area?
      3. Are the obscured features ornamental, decorative or otherwise significant?
      4. 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

1. 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.

1. 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.
2. Remove exposed electrical installations and install in a concealed location.
3. 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 pre-wet surfaces.
4. Replastering:
   1. General:
      1. 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.
      2. 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 or 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.
   7. Sand smooth toweled finishes lightly to remove trowel marks and arises.
   8. 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.
   9. See 09200-03-R and 09215-01-R for additional guidance in plastering.
5. 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:
      1. Do all cutting, patching, repairing and pointing of plaster work after other work is in place, and at such times as directed.
      2. Execute pointing around fixtures, outlet boxes, switches, plates, fitting, piping, conduit, registers, frames and other appliances abutting or extending through the plaster.
      3. 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.
      4. Patched area shall match adjoining work in texture and finish.
      5. For patching existing work, cut back to sound plaster on straight lines and back bevel edges to remaining plaster. Provide new accessories as required.
      6. 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.
      7. 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:
      1. 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.
      2. 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.
      3. Butter joints between precast and precast, and between precast and existing, so that they are not visible to the eye.
      4. Installed and completed installation shall not give the appearance that repair or restoration work has been performed, and be acceptable to the Contracting Officer.
      5. For additional guidance, see 09200-05-R and 09200-11-R.
6. 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

1. 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.
2. Mop floors clean of refuse and debris. Take precautions to prevent unnecessary staining and smearing of floors.
3. Protect finished plaster work against damage, and from freezing or premature drying out.
4. Marking or writing on finished plaster surfaces will not be permitted. The Contractor shall strictly enforce observance of this requirement.
5. Protect plaster repair areas against too rapid drying, based on manufacturer’s instructions.