Guide Specification for Interior Ornamental Plaster

NWCB Technical Document 11/94 INTERIOR PLASTER Guide Specification for Interior 700-400 Ornamental Plaster

Specification Reference: Framing & Lathing – ASTM C841 Plastering – ASTM C842

1. General 1.1 Execute ornamental lath and plaster in accordance with scale details shown on drawing.

2. Framing and Lathing 2.1 Install framing and lathing of cold rolled lather’s channel or pencil rod with wire ties 3.4lb metal lath to a rough shape of the required detail, allowing a minimum plaster thickness of ¾”.

3. Run Plaster 3.1 Apply scratch coat of sanded base coat plaster to the metal lath. 3.2 Run cornices and moldings full, straight and true with molding plaster, using clean cut metal conforming to the profiles shown on drawings. 3.3 Align lines accurately with square intersections and accurate miters at corners and angles.

4. Cast Plaster 4.1 Prepare enriched ornamental work which cannot be run in place with molding plaster or gypsum cement cast in reusable silicone rubber molds. 4.2 Back the work with jute, burlap, fiberglass mesh, galvanized wire or mechanical fasteners as required for strong attachment to the substrate. 4.3 Reinforce castings with wood fiber, fiberglass strands, fiberglass mesh, galvanized metal lath or wire.

5. Finishing 5.1 Make all joints carefully and point neatly so as to be invisible. Sandpaper rough spots and leave the entire work ready for decoration.

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1. Brackets were laid out and shaped using 1” x 3/16” flat iron 2. Carrying channels were erected using 1-1/2” channel supported by anchoring into holes tapped into the concrete wall and anchors tapped and plugged into the ceiling (at a maximum of 4” spacing) 3. A water level line was used to lay out the position of brackets on the wall and a chalk line was snapped at the ceiling line of the brackets. 4. Brackets were fastened to the wall using concrete anchors or nails 5. Furring channels were tied on at each member at bends. 6. The ¾” channel furring was tied (at the points where they crossed the brackets) to the carrying channel and at one point to the wall using No. 14 gauge galvanized annealed wire. 7. 3.4 lb diamond mesh lath was bent to shape on a bench edge or plank and tied to furring.

On very large cornices, it may be necessary to provide additional bracing for rigidity with rod or channel stiffeners placed diagonally as required to make a good stiff job.

Cornices with Stuck Member A stuck member is a molding which has been precast in a shop and is stuck to the cornice. The plasters do this by scratching the surface of the base coat plaster and applying molding plaster which adheres to both the precast piece and the base coat.

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 2 OF 2