Slideshow: Making Replacement Pieces

Making the Wax Impression

Intact motifs on the existing plaster ceiling were selected to make the replacement pieces. Here, William Bisson masked off a “sun” motif with painter’s tape, then applied petroleum jelly to the existing painted surface to help release the impression from the ceiling (photo, left). He then brushed on several coats of flex wax over the motif to a minimum thickness of 3/32 inch (photo, right).

Prepping the Wax Mold

Once hardened, the wax impression was removed from the ceiling (photo, left). Apprentice Derek Dawson then removed the painter’s tape and prepped the wax negative for mold making (photo, right).

Prepping the Mold’s Saddle

While Ron trimmed up the wax impression (photo, left), William and Derek mixed fast-drying gauging (gypsum) to make the bottom, or saddle, of the mold (photo, right).

Applying Spray Oil

To help the plaster replacement pieces release easily from the mold, the wax impressions were first sprayed with cooking oil. Here, the backs of two wax pieces were sprayed in preparation to make mold saddles.

Forming the Saddle

The fast-drying gauging plaster was poured over the wax impressions (photo, left), then leveled to create the mold’s saddle—a flat surface needed to make the thin, replacement pieces (photo, right).

Forming the Replacement Pieces

After 20 minutes or so, the saddles were flipped over and their wax negatives were sprayed with cooking oil. A super-hard, highly-refined molding plaster (Hydrocal) was then poured over the wax impressions to make the flat-work pieces. They too were leveled flat, similar to the saddles (photos, above).

Releasing the Mold

The Hydrocal molding plaster cures quickly. After 5 minutes, the mold’s saddle was removed (photo, left), then the thin, Hydrocal replacement piece (photo, right). The replacement piece is later trimmed down and scribed to the damaged area.

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