How to Make Crown Molding from Plaster of Paris

Last Updated: July 28, 2022

It's easy to make your own crown molding, especially if you just need a small piece to fill a gap. All you need is some gypsum, also known as plaster of Paris, and some clay for making a mold. Our how-to guide will show you how to turn these simple materials into realistic-looking fake plaster molding!

Steps

1
Roll out a thick piece of clay and press it onto a piece of crown moulding. Thickness adds strength which is needed later when pouring the plaster.
2
Peel the clay off and straighten out minor bends. The clay should be an exact reverse replica of the crown moulding.

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3
Reinforce walls with wood pieces and/or strong plastic. Seal edges to contain the poured plaster.
4
Mix plaster of Paris and pour a little in the mould. Ensure that the nooks and crannies are filled before pouring enough plaster to fill the mould. Your fill line will be the thickness of the crown moulding.
5
Discard the clay and let the plaster dry until it feels dry to the touch.
6
Trim as needed. Handle the dry plaster moulding carefully to prevent chipping.
7
Ignore any tiny air pockets for now.
8
Spread a thin layer of glue on all contact points.
9
Insert the plaster moulding into the gap without force. It should fit snugly.
10
Once the glue is dry, fill any air bubbles and gaps with caulking. Wipe off excess caulking with a slightly damp and smooth cloth.
11
Once you're satisfied that the gaps and surface are seamless, prime and paint as needed.

Warnings

Keep the clay you use to make the plaster mould completely separate from clay used to make pottery. Plaster bits don't shrink when fired in a kiln. Since clay shrinks when fired, pottery would break around the plaster.

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