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FAQ's - Installation of Plaster Cornice

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1. Wall Preparation
Prior to installing our fireproof plaster cornice in an area with drywall construction, first screw ½" plywood strips to the studs around the entire room using drywall screws. The strips should be as wide as possible yet still be able to fit in the hollow space behind the cornice. With masonry or concrete walls, the wood ground strips must be secured in place with masonry anchors and construction adhesive. These wood strips will hold the drywall screws, which will be used to fasten the cornice in place.

2. Layout
In laying out the room, particular attention must be given to outside corners. Mismatches in pattern are most obvious at these points and must be avoided. The cornice should start in a corner and run to the next corner. Never run towards the center of a wall from two opposite corners as this will certainly result in an obvious mismatch where they meet. Cornices, which feature brackets and coffers, must be laid out with particular care in order to avoid problems at the inside and outside corners. If a mismatch has to occur, make sure it happens at the most inconspicuous corner in the room.

3. Installing
First establish the drop of the cornice down the wall and put a pencil mark every 24" all the way around the room. These marks will be your guide as you install the cornice. The drop dimension must match the drop measurement on your miter box. The miter box can be fabricated with 1"x and 2"x lumber of the appropriate width. The box will then be marked and sawed down with 45 degree and 90 degree cuts.

Most cornices are approximately 6ft long and the casts need to be pre-drilled near each end and then in 2-3 locations evenly spaced between. The holes must have a slightly larger counter-sunk hole going slightly below the surface in order to hide the heads of the screws.

Using drywall screws of the appropriate length, the cornices are then screwed in place to the plywood ground behind the mouldings. Sometimes the wall might not be true and the cornice might slightly crack with an audible sound as the screws draw the moulding tightly to the wall. This is normal and not harmful due to the fiber reinforcement in the castings. The bottom edges must be held on the drop marks. Any butt and miter joints, which do not fit tightly together, can be back cut with a handsaw or block plane for a snug fit in these areas. Keep in mind that voids and openings in plaster mouldings can be easily filled and corrected during the pointing and patching phase of the job. If one moulding is lower and does not line up with the adjacent one, wood shims can be placed behind it's edge prior to tightening down the end screws to insure a smooth, even joint between one cast and another.

4. Pointing and Patching
The last step in the installation requires that the screw holes, cracks, gaps in the miters and the reveals where the cornice meets the wall and the ceiling be patched and pointed in. The long joint at the ceiling and walls will need to be carefully caulked with a quality paintable caulk. Screw holes, miter joints and butt joints can be filled with hand mixed plaster or premixed non-shrinking spackle. When patching with hand mixed plaster, be sure to wet the area to be patched with a paintbrush and clean water before applying the plaster. Hand mixed plaster patches beautifully if it is applied to a dampened area. Either the plaster or spackle can be applied with a small flat bladed pointing tool. As the patch is about to set, utilize a small damp brush to smooth over the area and create a very finished effect.