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NWCB Technical Document 06/04 EXTERIOR SYSTEMS Guide Specification for 600-103

1. General 1.1 Work included under this section for lathing and plastering: The contractor shall provide all labor, materials and equipment necessary to complete the job as shown on drawings and/or described herein. 1.2 All required flashings except those providing ground for plaster shall be installed by others. 1.3 Details of workmanship and installation not specified herein shall conform to the Northwest allW & Ceiling Bureau’s standards and recommendations: 1.3.1 NWCB guide Information 600 Series – as they apply. 1.3.2 NWCB Stucco Resource Guide, current edition. 1.3.3 ASTM C-1063 , Lathing and Furring for Portland cement plaster 1.3.4 ASTM C-926 Application of Portland cement plaster 1.3.5 Where products and systems are specified or used, they shall be installed per manufacturer’s directions. 1.4 Applicator must be able to reference projects of equal scope 1.5 Contractor to provide samples (if required). Do not proceed until samples are reviewed and approved by architect/owner. 1.6 Contractor to be a member of the NWCB in good standing. 1.7 Deliver manufactured materials in unopened containers with label intact 1.8 Materials shall be protected from damage to the elements (rain, freezing, etc) 1.9 Environmental conditions: Cold Weather: Do not use frozen materials. Do not apply plaster to frozen surfaces. Do not apply plaster when ambient air temperature is less than 35 degrees F. If a potential for freezing exists, an approved admixture may be used. Hot Weather: Protect plaster from uneven or excessive evaporation. Moist cure if temperature is above 77 degrees F or relative humidity is below 70%.

2. Products 2.1 Sheathing: ASTM C-79 treated core or a proprietary sheathing meeting the standards of the NWCB. 2.2 Weather-Resistive Barrier: To meet Fed. Spec. UU-B-790a or AATCC-127 and have a minimum 30 minute water-resistance rating and have a minimum water vapor transmission of 35 grams per square meter in 24 hours. Minimum 2 layers over all types sheathing. 2.3 : The type and configuration of lath is determined by the style of construction. All lath shall be self- furred over sheathing. All exterior lath shall be galvanized. 2.3.1 ASTM C-847 Expanded metal lath 2.5 or 3.4 lb per sq. yd.: Diamond Mesh, for soffits only (Flat rib, Hi Rib). 2.3.2 ASTM C-1032 Woven wire lath: 17 gauge x 1 ½ inch openings 2.3.3 ASTM C-933 Welded wire lath 16 or 17 gauge. 2.4 Accessories: Shapes used as grounds sized to provide the required thickness of plaster. All accessories

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© NORTHWEST WALL AND CEILING BUREAU to be either galvanized, zinc, Aluminum or Polyvinylchloride (PVC). 2.4.1 Cornerbeads: Shall be welded wire open mesh type to allow plaster to fully engage bead. Plastic nose for an acrylic finish coat and metal nose for a cement finish coat. 2.4.2 Casing Beads: May be expanded flange or short flange. 2.4.3 Control Joints: one-piece components and shall be a type with a lip or method to lock or engage the plaster membrane. 2.4.4 Weep screeds: Shall have a minimum 3 1/2 inch nail flange and be a type that allows moisture to escape. 2.4.5 Expansion Joints: Two or three piece telescoping accessories.

2.5 Plaster materials: 2.5.1 Portland Cement: ASTM C-150 Type I/II 2.5.2 Cement: ASTM C-91 2.5.3 Plastic Cement: ASTM C-1328 2.5.4 -Hydrated : ASTM C-206 2.5.5 Washed Sand : ASTM C-897 , ASTM C-144 2.5.6 Water: clean and potable 2.5.7 Fibers 1/2 long ASTM C-1116 2.5.8 Optional Additives: 2.5.8.1 Air entraining approved by architect/NWCB 2.5.8.2 Water reducers approved by architect/NWCB 2.5.8.3 Winter admixtures approved by architect/NWCB 2.5.8.4 Natural colors for cement finish coats or factory prepared finish coat. 2.5.8.5 Acrylic finish coat approved by architect/NWCB 2.5.8.6 Venetian finish approved by architect/NWCB 2.5.8.7 Cement plaster specified for paint shall be a vapor permeable paint and be made for stucco ( alkali-resistant) 2.5.9 Mix Designs (choose one A,B,C,D) Parts per volume. A. 1 portland cement, 1 masonry cement, 3-5 (per sum total of cement) sand B. 1 portland cement, 1/2 to 3/4 lime, 3-4 (per sum of cement and lime) sand. C. 1 plastic cement, 3 1/2 - 4 1/2 (per sum of cement and lime) sand. D. Proprietary stucco basecoat approved by architect/NWCB (Fibers shall be added to all designs) 2.5.10 Finish Coat 2.5.10.1 1 white cement (or regular), 1-2 lime, 3 –3 1/2 sand (16/20 medium sand finish) or (20/30 fine sand finish). 2.5.10.2 Fog Coat- (integrally colored cement finish only) per manufacturer.

2.5.11 Accurately proportion materials for plaster batch with measuring devices of known volume. Shovel count for sand is acceptable after standardization is established. 2.5.12 Mix with an approved style mixer for plaster, do not over mix, do not re-temper.

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www.nwcb.org © NORTHWEST WALL AND CEILING BUREAU 3. Execution 3.1 Attach weather-resistive barrier (WRB), lath and accessories per NWCB Stucco Resource Guide and ASTM C-1063. Apply WRB complete exceeding minimum code required laps and in a “shingle-” to integrate with flashings (by others) to allow water to shed and exit at base of wall (weepscreed) or a flashing point. Lath shall be applied across (perpendicular) to framing supports and well lapped. Fasteners shall penetrate a minimum 3/4 inch into wood framing (studs/joists) and be attached 6 to 7 inches on center along the framing support. 3.2 Control joints may be applied over the lath, layout of control joints shall be per drawings or architect/owner. 3.3 Vertical control joints shall pass through horizontal control joints, but not horizontal expansion joints. 3.4 All terminations of control joints in weather (rain) exposed locations shall be set in a bed (daub) of sealant. 3.5 Horizontal expansion joints shall have the lath cut and lap the nailing flanges. 3.6 All accessories shall be securely fastened to structure prior to plastering. 3.7 Nominal thickness of plaster: First (scratch) coat : 3/8 to 1/2 inch Second (brown) coat: 3/8 to 1/2 inch Finish coat: 1/8 inch or less Total nominal thickness of basecoat to be a minimum 3/4inch (except over CMU or see PCP-622). Fire-rated assemblies shall be a minimum 7/8 inch thick. 3.8 Plaster may be applied by hand or with plaster pumps. Prior to using a plaster pump, the contractor shall verify experience pumping cement plaster. 3.9 Apply first (scratch) coat with sufficient pressure to embed lath and trim flanges. 3.10 Cross rake (horizontal) to provide key for brown coat. 3.11 Apply second (brown) coat with sufficient pressure to ensure tight contact with scratch coat. Rod to a true and even plane. Tolerances shall be within a 1/4 inch in ten feet. 3.12 Floating: The brown coat shall be floated with a “hard” float to densify and compact the brown coat. Hard floating to be done when the surface (sheen) moisture has started to disappear. The float shall be cork, wood shingle or semi-rigid neoprene. A sponge float is not acceptable. 3.13 Curing: Brown coat may be applied as soon as the scratch coat has attained sufficient rigidity to receive the brown coat. Brown coat must cure a minimum 7 days prior to applying finish coat.

Finish coat: The finish texture to be ______Sand Finish (fine, medium, heavy) Machine Dash (fine, medium, heavy) Knockdown Dash Lace Finish Comb Finish Mission or Santa Barbara Finish English Finish Smooth Trowel (not recommended for cement finish)

Apply finish coat with wet edge from architectural break to architectural break.

The Northwest Wall and Ceiling Bureau recommends that you refer to the current edition of the Stucco Resource Guide for more comprehensive specifications and detailing when using stucco.

This technical document is to serve as a guideline and it is not intended for any specific construction projects. NWCB makes no express or implied warranty or guarantee of the techniques, construction methods or materials identified herein. PAGE 3 OF 3

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