Making a plaster mold

mold making putty

With a this missing piece of the ceiling, this post shows how to make a plaster mold.  We don’t make a habit out of fixing plaster or making molds, but for small, spot repairs, it makes sense that we do it.   It’s always good to have skills that expand beyond painting.

A small ornament was destroyed when it fell from the ceiling.  It would have to be re-created using a mold.  See previous related posts:  Part 1: Frick Collection Ceiling Repair and Part 2:Plaster Repair.

mold making puttyA putty was made out of a dental-like mold (fast-drying) and thoroughly pressed onto the model.  We just followed the instructions on the box — mixing the 2 ingredients together which makes a pliable elastic mold that dries fast.

mold making puttyWhen making a mold, you need a model in good condition.   Quickly after mixing the putty, we placed it on a model piece and thoroughly pressed it.

mold making putty let dryThe putty dried to a perfect print of missing section.

mold fillingA liquid slurry (consistency of sour cream) was mixed and poured into the cast.

mold fillingIn order to fill the area completely, a wall of blue tape was arranged.  Using a palette knife, the mixture was pressed down and compacted.  This is very important.

mold fillingDried plaster.

mold preparationGently break away excess or cut it away to avoid breaking the mold.

mold preparationFreshly pulled out of the mold.

mold preparationLet the mold dry completely.  At the museum, we had the convenience of this kiln to assist with drying (at low temperature).  Otherwise, be sure to dry to cure (6-12 hours).

mold preparationUsing specialized chasing tools, scrape away excess.

mold preparation

mold preparationEtch the backside so the wet plaster can adhere well.

mold preparationCleaned and ready to go.

mold preparationUsing a marker, signify extra areas to cut off.

mold preparationCut off excess.

mold preparation

mold preparationMix the plaster of Paris and Wellbond to “glue” the ornament on the backside.

mold preparationAdditional carving and shaping was needed.

mold preparationUse extra plaster to filling the gaps on the surface.

mold finishedShellac was used on the surface to seal the plaster.

mold shellacFinish the ornament with base paint, decorative finish as further explained in post: Ceiling repair at Frick Collection.

mold base paint

mold finishSee also Part 1, Part 2 of this series.

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