Technical Procedures Disclaimer
Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.
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We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.
PART 1 - GENERAL
1.01 SUMMARY
- This procedure includes guidance on applying plaster veneer over a gypsum base. This also includes the following work:
- Steel framing members to receive gypsum base.
- Gypsum base screw-attached to steel framing and furring members.
- One-component veneer plastering over gypsum base.
- Screw type metal support system and furring are specified elsewhere in Division 9.
- Shaft walls constructed with gypsum base face layers are specified in Division 9 specification for Gypsum Board Shaft Wall Systems.
- See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
- Safety Precautions
- Historic Structures Precautions
- Submittals
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- 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 DEFINITIONS
- Gypsum Board Construction Terminology: Refer to ASTM C11 for definitions of terms for gypsum board construction not otherwise defined in this procedure or other referenced standards.
1.03 SYSTEM DESCRIPTION
- Performance Requirements:
- Fire-Resistance Ratings: Where indicated, provide materials and construction which are identical to those of assemblies whose fire resistance rating has been determined per ASTM E119 by a testing and inspecting organization acceptable to authorities having jurisdiction.
- Provide fire-resistance-rated assemblies identical to those indicated by design designations in U.L. “Fire Resistance Directory” or in listing of other testing and agencies acceptable to authorities having jurisdiction.
- Fire-Resistance Ratings: Where indicated, provide materials and construction which are identical to those of assemblies whose fire resistance rating has been determined per ASTM E119 by a testing and inspecting organization acceptable to authorities having jurisdiction.
1.04 SUBMITTALS
- Product Data: Submit manufacturer’s product specifications and installation instructions for each veneer plaster and gypsum basecoat component, including other data as may be required to show compliance with this procedure.
1.05 QUALITY ASSURANCE
- Qualifications: Single Source Responsibility: Obtain veneer plaster products (gypsum base, joint reinforcing, and veneer plaster) from a single manufacturer for each veneer plaster system indicated.
1.06 DELIVERY, STORAGE AND HANDLING
- Packing and Shipping: Deliver materials in original packages, containers or bundles bearing brand name and identification of manufacturer or supplier.
- Acceptance at Site: Handle gypsum base to prevent damage to edges, ends, and surfaces. Do not bend or otherwise damage metal corner beads and trim.
- Storage and Protection: Store materials inside under cover and keep them dry and protected against damage from weather, direct sunlight, surface contamination, corrosion, construction traffic and other causes. Neatly stack gypsum base flat to prevent sagging.
1.07 PROJECT/SITE CONDITIONS
- Environmental Requirements:
- General: Establish and maintain environmental conditions for application of veneer plaster to comply with ASTM C843 and with veneer plaster manufacturer’s recommendations.
- Minimum Room Temperatures: For adhesive attachment of gypsum base and application of veneer plaster, maintain not less than 50 degrees F. (10 degrees C.) nor more than 80 degrees F. (27 degrees C.) for one week prior to application and continuously thereafter until veneer plaster has fully dried. Distribute heat evenly; prevent concentrated or uneven heat on veneer plaster near heat source.
- Ventilate building spaces to remove water not required for hydration of veneer plaster materials. Avoid conditions which result in veneer plaster drying too rapidly.
PART 2 - PRODUCTS
2.01 MANUFACTURERS
- Georgia Pacific Corp.
www.buildGP.com - National Gypsum Co.
Gold Bond Building Products Division
www.nationalgypsum.com - USG Corporation
www.usg.com
2.02 MATERIALS
- Gypsum Board Products:
- General: Provide gypsum boards of type indicated in maximum lengths available to minimize end-to-end joints.
- Gypsum Base for Veneer Plaster: ASTM C588, of types and thicknesses indicated below; with square or tapered long edges as standard with manufacturer; and as follows:
- Type: Type X for fire-resistance-rated assemblies.
- Thickness: 5/8” unless otherwise indicated.
- Gypsum Backing Board for Multi-Layer Applications: Gypsum backing board, ASTM C442; or gypsum base, ASTM C588; or gypsum wallboard, ASTM C36, as recommended by manufacturer for application method indicated; and as follows:
- Type: Type X for fire-resistance-rated assemblies.
- Thickness: 5/8” unless otherwise indicated.
- Joint Reinforcing Materials:
- General: Provide joint reinforcing materials indicated which comply with joint strength requirements of ASTM C587 and are acceptable to veneer plaster manufacturer for application indicated.
- Joint Tape: Paper.
- Joint Tape: Open-weave glass fiber fabric.
- Embedding Material for Joint Tape: As recommended by veneer plaster manufacturer for use with joint tape material indicated.
- For high strength veneer plaster and paper tape, use setting-type joint compound.
- Veneer Plaster Materials:
- One-Component Regular Veneer Plaster: ASTM C587, manufacturer’s standard one-component veneer plaster for application directly over the following without use of separate base coat material such as Dens-Cote (Georgia Pacific Corp.), Gold Bond Uni-Kal Plaster (Gold Bond Building Products Div., National Gypsum Co.), Diamond Veneer Finish (USG Corp.), or approved equal.
- Two-Coat Veneer Plaster: Veneer plaster shall be by the same manufacturer as the gypsum base where installed over gypsum base conforming to ASTM C587, such as Imperial Basecoat and Imperial Veneer Finish Coat (USG Corp.), Gold Bond KLING Base Coat Veneer Plaster and Uni-Kal Veneer Plaster(Gold Bond Building Products Div., National Gypsum Co.), or approved equal.
- Finish Coat Aggregate: As required to match adjacent surface.
- Miscellaneous Materials:
- General: Provide auxiliary materials for veneer plaster construction which comply with referenced standards and the recommendations of veneer plaster manufacturer.
- Bonding Compound for Interior Plastering: ASTM C631.
- Laminating Adhesive: Special adhesive recommended for laminating gypsum base face layers to base layers of gypsum board in multiple layer construction.
- Spot Grout: ASTM C475, setting-type joint compound of type recommended for spot grouting hollow metal door frames.
- Gypsum Base Screws: ASTM C1002.
- Concealed Acoustical Sealant: Non-drying, non-hardening, non-skinning, non-staining, non-bleeding, gunnable sealant such as “Sheetrock Brand Acoustical Sealant” (USG Corp.), or approved equal.
- Sound Attenuation Blankets: Unfaced mineral fiber blanket insulation produced by combining mineral fibers of type described below with thermosetting resins to comply with ASTM C665 for Type I (blankets without membrane facing) such as “Thermafiber SAFB (sound attenuation fire blankets), or approved equal.
- Mineral Fiber Type: Fibers manufactured from glass or slag.
- Insulation shall have a flame spread rating of 15 or less with a smoke developed of 0 when tested per ASTM E84.
2.03 ACCESSORIES
- Trim Accessories:
- Provide cornerbeads, edge trim and control joints of material and, for edge trim, shapes indicated below which comply with ASTM C1047 and veneer plaster manufacturer’s recommendations for application indicated.
- Material: Formed metal or metal combined with paper; with metal complying with the requirement; sheet steel coated with zinc by hot-dip or electrolytic processes, or with aluminum.
2.04 MIXES
- Veneer Plaster Mixes: Mechanically mix veneer plaster materials to comply with referenced veneer plaster application standard and with recommendations of veneer plaster manufacturer.
PART 3 - EXECUTION
3.01 EXAMINATION
- Examine substrates which veneer plaster construction attaches to or abuts including preset hollow metal frames, cast-in-anchors, and structural framing, with installer present, for compliance with requirements for installation tolerances and other conditions affecting performance of veneer plaster construction. Do not proceed with installation until unsatisfactory conditions have been corrected.
3.02 ERECTION, INSTALLATION, APPLICATION
- Application of Gypsum Base, General:
- Gypsum Base Application Standard: Comply with ASTM C844.
- Apply gypsum base to framing in accordance with ASTM C844. Apply base with long dimension parallel to studs and attach with 1 inch Type S screws, spaced 8 inches on center around the perimeter and 12 inches on center on the intermediate stud. Do not force base in place; stagger end joints of adjoining boards. All butting ends and edges of base shall occur over supports.
- Erection Tolerance: No more than 1/16 inch offsets between planes of gypsum base faces, and 1/8 inch in 8’-0” for plumb, level, warp and bow.
- Install sound attenuation blankets as indicated, prior to gypsum base unless readily installed after base has been installed.
- Locate exposed end-butt joints as far from center of walls and ceilings as possible, and stagger not less than 24 inches in alternate courses of base.
- Install gypsum base for walls/partitions in manner which minimizes the number of end-butt joints or avoids them entirely where possible. At stairwells and similar high walls, install gypsum base horizontally with end joints staggered over studs.
- Install gypsum base with face side out. Do not install imperfect, damaged or damp boards. Butt boards together for a light contact at edges and ends with not more than 1/16 inch open space between boards. Do not force into place.
- Attach gypsum base to steel studs so that leading edge or end of each board is attached to open (unsupported) edge of stud flange first.
- Attach gypsum base to supplementary framing and blocking provided for additional support at openings and cutouts.
- Spot grout hollow metal door frames for solid core wood doors, hollow metal doors, and steel doors 3 feet 4 inches wide. Apply spot grout at each jamb anchor clip just before inserting gypsum base into frame.
- Form control and expansion joints in veneer plaster surfaces at locations indicated, with space between edges of gypsum base, prepared to receive trim accessories.
- Cover both faces of steel stud partition framing with gypsum base in concealed spaces (above ceilings, etc.), except in chase walls which are properly braced internally.
- Except where concealed application is required for sound, fire, air or smoke ratings, coverage may be accomplished with scraps of not less than 8 sq. ft. area, and may be limited to not less than 75% of full coverage.
- Fit gypsum base around ducts, pipes, and conduits.
- Isolate perimeter of non-load-bearing veneer plaster partitions at structural abutments. Provide 1/4 inch to 1/2 inch space and trim edge with “U” bead edge trim. Seal joints with acoustical sealant.
- Where sound-rated veneer plaster construction is indicated, including double-layer work and work on resilient furring, seal construction at perimeters, control and expansion joints, openings and penetrations with a continuous bead of acoustical sealant including a bead at both faces of partitions. Comply with ASTM C919 and manufacturer’s recommendations for locations of edge trim, and close off sound flanking paths around or through construction including sealing of partitions above acoustical ceilings.
- Space fasteners in application of gypsum base to comply with referenced gypsum base application standard and manufacturer’s recommendations.
- Methods of Gypsum Base Application:
- Single-Layer Application: Install gypsum base as follows:
- On partitions/walls apply gypsum base vertically (parallel to framing), unless otherwise indicated, and provide sheet lengths which minimize end joints.
- On partitions/walls 8’-1” or less in height apply gypsum base horizontally (perpendicular to framing); use maximum length sheets possible to minimize end joints.
- Fasten with screws.
- Double-Layer Application: Install gypsum backing board for base layer and gypsum base for face layer as follows:
- On partitions/walls apply base layer and face layers vertically (parallel to framing) with joints of base layer over supports and face layer joints offset at least 10 inches with base layer joints.
- Fasten base layers with screws and face layer with adhesive and supplementary fasteners.
- Single-Layer Application: Install gypsum base as follows:
- Installation of Trim:
- General: Where feasible, use same fasteners to anchor trim accessory flanges as required to fasten gypsum base to supports. Otherwise, fasten flanges to comply with veneer plaster manufacturer’s recommendations.
- Install corner beads at external corners.
- Install metal edge trim where edge of gypsum base would otherwise be exposed or semi-exposed. Provide type with face flange to receive joint compound.
- Install bead where veneer plaster construction is tightly abutted to other construction.
- Install metal corner beads at external corners of veneer plaster work.
- Install control joints at locations indicated, or if not otherwise indicated, at spacings and locations required by referenced gypsum base application standard.
- Installation of Joint Reinforcement:
- Reinforce interior angles and flat joints in gypsum base with joint tape and embedding material to comply with referenced gypsum veneer plaster application standard and with veneer plaster manufacturer’s recommendations.
- Veneer Plastering:
- Gypsum Veneer Plaster Application General:
- Plasterer shall be responsible for determining the most effective procedure for cutting and time lapse between coats based on job conditions. Plaster which is cracked or crazed due to improper timing, curing or any other reason shall not be accepted. Remove and replace unacceptable plaster, including gypsum base and bonding agent if damaged during removal of defective plaster.
- Gypsum Veneer Plaster Application Standard: Apply gypsum veneer plaster to comply with ASTM C843 and veneer plaster manufacturer’s recommendations.
- Grout frames solidly and continuously where indicated or required for fire-resistance ratings; otherwise spot-grout at each anchorage point by encasement of anchor devices in plaster bed.
- Concealed Surfaces: Omit veneer plaster in areas where plaster will be concealed from view when completed work, but do not omit veneer plaster behind cabinets, furniture, furnishings and similar removable items.
- Provide smooth trowel finish, unless otherwise indicated to match existing adjacent surfaces.
- Provide texture finish matching existing, in locations indicated.
- For Two-Coat Applications:
- Base Coat Application: Fill metal trim and joint base with tight, thin coat of base coat plaster material. Allow to set before proceeding with work. After bed has set up, scratch in a tight, thin coat of basecoat plaster over entire area, immediately doubling back with plaster from same batch to full thickness of 1/16 inch. Fill voids and imperfections. Leave surface rough or cross-rake with fine wire rake. Allow basecoat to set to provide proper suction for finish coat.
- Finish Coat Application: Scratch in and double-back with finish plaster to fill out to a smooth, dense surface, free from “cat faces” and other irregularities or blemishes. Final trowel after surface has become firm, holding trowel flat and using water sparingly. Do not over trowel. Overall veneer plaster thickness shall be 1/8 inch.
- Grounds: Where frames and other units in the veneer plastering act as grounds (not including trim accessories) for flush plastering, groove finish coat at juncture with the other work.
- Gypsum Veneer Plaster Application General:
3.03 ADJUSTING/CLEANING
- Remove temporary coverings used to protect other work.
- Remove plaster spillage promptly from door frames, windows and other adjoining work. Repair surfaces which have been damaged by plastering work.
- Patching: Cut out broken and damaged plaster to straight lines. Cut out cracks to width of not less than one inch. Fill areas to be patched with base material. Apply finish coat of same material; patched area shall match adjoining work.
3.04 PROTECTION
- Provide final protection and maintain conditions, in a manner suitable to installer, which ensures that veneer plaster work being without damage or deterioration at time of substantial completion.