Techniques for Plaster Impressions and Imprints

Urethane Rubber Molds

• Urethane rubber comes in both liquid and paste forms. Contractors use paste urethane to make impressions of in-place ceiling and wall decorations. This method works well to copy a historic ornament without removing and possibly damaging it. Contractors use liquid urethane in a process called flood molding. They mount the object inside a liquid-tight box, coat it with liquid soap, and pour the liquid urethane around the object until it fills the box. Urethane dries overnight, and produces a reusable rubber mold for use with plaster and composition formulas. Composition formulas differ from plaster in that they contain glue and linseed oil to make them flexible when dry.

Sheet Metal Templates

• Skilled plaster specialists use sheet metal templates to create smooth plaster borders. They transfer the profile of the desired border, often a replica from a historic building, onto a piece of sheet metal. Then they cut the pattern out, and mount the sheet metal to a piece of wood of equal length to stiffen the template. The entire cut-out shape of the template must extend beyond the edge of the board to create the correct border shape. To create the plaster border, the specialist applies a thick layer of plaster to the wall, places the template against the wall, and applies pressure as he pulls it across the wet plaster. He may repeat the process multiple times to completely fill out a wide border template.

Stencils

• Plaster specialists and do-it-yourselfers use pre-cut plastic or homemade cardboard and masking tape stencils to create three-dimensional designs and textures. The open space in a stencil becomes the positive design on the plaster surface, and the stencil thickness matches the thickness of the finished design. Attach stencils to the wall or ceiling with tape, and use a putty knife to evenly fill the open spaces with plaster. Remove the stencil, allow the plaster to fully dry and gently finish undesired rough edges with a fine-grit sandpaper.

Imprints

• Easy to do yourself, imprinting techniques create beautiful designs and textures on plaster surfaces. Gently push household objects such as feathers, plant leaves, shells, rocks or figurines into partially dry, but still soft plaster. Paint dry plaster imprints with liquid or tinted dry powder paint to create added contrast.