GUIDE SPECIFICATION FOR PATCHING WITH LATH AND PORTLAND CEMENT PLASTER
PART I: GENERAL
Scope of Work: Work included under this section of the specification for lathing and plastering. The contractor shall provide all labor, materials and equipment necessary to complete patching as shown on the drawings and/or described herein.
General Requirements: Compliance with standards and industry specifications: Northwest Wall & Ceiling Bureau (NWCB) standards (206) 524-4243 The Northwest Wall and Ceiling Bureau Stucco Resource Guide ASTM: C1063 - Installation of Lathing and Furring for Portland Cement Plaster ASTM C926 - Application of Portland Cement Plaster Where products are specified they shall be installed in accordance with local building codes and/or manufacturers recommendations.
Contractor Qualifications: Applicator/contractor must be qualified in the workmanship of lathing and plastering and a member of the NWCB. Shall be approved by architect.
Submittals: Applicator/contractor shall be prepared and may be required to supply samples.
Quality Control: Attend a pre-Installation meeting. Applicator/contractor shall be prepared for third party inspections by qualified persons or agency.
Environmental Conditions: Reference NWCB Stucco Resource Guide. Acrylic and cement finishes have varying requirements for environmental conditions. Protect all material from freezing. Do not apply materials to frozen surfaces. Moist cure cement if required to insure a proper cure. Do not attempt work in unsatisfactory environmental conditions.
PART II: MATERIAL
- Grade D 60-minute asphalt saturated kraft paper
- b. 15 lb. felt (repair work only)
Lath: Galvanized (self furring)
- Expanded metal lath (2.5 lb/yd or 3.4 lb/yd)
- Accessories: casing beads, channel reveals, control joints, expansion joints to match existing in style, material and ground thickness. Asphalt Emulsion (if required)
- Portland cement: ASTM C150 Type I/II
- Portland cement ASTM C618 Type IP
- Masonry cement ASTM C 91
- Lime ASTM C206 Type S
- Sand: ASTM C144 or C897 "washed" plaster or masonry sand
- Fibers ASTM C 1116: glass, nylon or polypropylene -1/2 inch long
- Bonding agent: ASTM C932
Mix Proportions: Per the NWCB Stucco Resource Guide or approved by architect
Cement Finish: Portland cement finish stucco pre-blended at factory or site mixed per NWCB Stucco Resource Guide
Skim coat: proprietary polymer enriched cement designed for use as an EIFS basecoat/adhesive. Follow manufacturers instruction for mixing.
Fiberglass mesh: 4-6 oz per square yard
Acrylic Finish: Proprietary acrylic finish approved by NWCB/architect
PART III: EXECUTION
Examination: Prior to starting lath and plasterwork, carefully inspect installed work of other trades. Notify architect or proper authorities in writing of any detrimental conditions before proceeding with work, including all flashings, framing, sheathing or unsatisfactory conditions in existing stucco finish. Owners shall be notified of any plants, trees, furniture, landscaping or other items that may need to be moved or protected.
Flashings: Installed by others
Weather-resistive barrier: Apply weather resistive barrier from bottom to top. Lap weather resistive barrier in shingle fashion with all flashings. Lap weather resistive barrier with existing weather resistive barrier. Seal any holes or damage to weather resistive barrier with a brushed on asphalt solution.
Trim Accessories: Properly install, miter and align trim accessories with existing trim accessories. Fasten all trim accessories to framing members 8 to 12 inches on center.
All intersections, miters, splices and terminations of control joints and channel reveals shall be set in a bed of sealant or back-sealed in a manner approved by architect.
Casing beads shall be set around windows to provide the specified joint design width.
Metal Plaster Base: Cut and fit lath neatly into patch area. An overlap with the existing lath is optimal if possible. The lath shall over lap the nailing flange of all casing beads, channel reveals or expansion joints. Control joints may be placed over the lath. Fasteners should be placed six inches on center along framing members. Fasteners should only be through the sheathing over solid framing members and not into sheathing between studs.
Plastering Protect all areas not to be plastered from damage.
Apply a bonder to edge of existing cement plaster to insure a good bond for new patchwork. Allow to get tacky before plastering.
All plaster work to be applied with hand tools.
Apply a scratch coat of Portland cement plaster approximately 3/8 inch thick. Scarify or score to provide keys for the brown coat. Brown coat may be applied as soon as the scratch coat has attained sufficient rigidity to receive brown coat. The brown coat shall be rodded off to produce a flat even surface with existing plaster. After the surface moisture has left the brown coat, the brown coat shall be hard floated to densify the plaster membrane. A hard neoprene, cork or shingle float shall be used. Moist cure brown coat for 3 days if relative humidity is below 70% and temperature is above 75 degrees F or windy conditions exist.
Follow finish procedure (methods 1-5) as chosen by owner/architect:
Finish coat shall be applied no sooner than 7 full days after brown coat has been applied. Apply finish coat and feather into and match existing texture.
Clean existing finish coat of dirt, grease, mold, algae or any substance that will prevent a proper bond of the new finish coat (use a bonding agent if needed). Finish coat shall be applied no sooner than 7 full days after brown coat has been applied. Apply finish coat over patch area and existing stucco. Work to architectural breaks and maintain a wet edge with finish. Match approved texture sample.
Clean existing finish coat of dirt, grease, mold, algae or any substance that will prevent a proper bond of the new skim coat. Provide a test area if there are any doubts of a proper bond. Allow brown coat to cure 5 days before applying skim coat. Spread skim coat over all surfaces to a uniform thickness of approximately 1/16 inch thick. Work to architectural breaks, no cold joints. Leave no surface irregularities that will not be covered by finish coat. Allow skim coat to dry before applying finish coat. Apply finish coat and maintain a wet edge to architectural breaks. Match approved texture sample.
Follow all instructions in method #3. While skim coat is wet, trowel a 4 to 6 inch strip of fiberglass mesh over the joint between the old stucco and new brown coat. Fully embed reinforcing mesh into the wet skim coat. Mesh may be butted or overlapped. Continue to follow the steps of method #3.
Clean existing finish coat of dirt, grease, mold, algae or any substance that will prevent a proper bond of the new skim coat. Allow brown coat to cure 5 days before applying the skim coat. Provide a test area if there are any doubts of a proper bond. Spread skim coat over all surfaces to a uniform thickness of approximately 1/16 to1/8 inch thick. Work to architectural breaks, no cold joints. Fully embed a reinforcing mesh into wet skimcoat, troweling from the center to the edge of the mesh, to avoid wrinkles. Mesh shall be continuous over all areas to be plastered. There shall be an overlap of reinforcing mesh of 2 inches. Leave no surface irregularities that will not be covered by finish coat. Allow skimcoat to dry before applying finish coat. Apply finish coat and maintain a wet edge to architectural breaks. Match approved texture sample.
Allow acrylic finish coat to "fully" set before removing protective cover from the elements.
CLEAN UP: All excess materials shall be removed from job site. Surrounding areas shall be clean and free of debris.