One problem in home restoration is how to repair a piece of decorative moulding for coving that is no longer manufactured or sold. Mouldings around fireplaces or light fixtures may be damaged or partially broken, or perhaps you've found a piece of architectural coving that you would love to reproduce and use elsewhere or in a bigger project. The solution is to take a latex rubber cast of the coving and use the cast to reproduce the original moulding.
Find a section of the moulding you want to reproduce in a length of up to a few feet.
Clean and sand the moulding to get it as near perfect as possible. Any blemishes will be reproduced in your mould.
Brush a coat of the latex mould onto the surface to be moulded. In the case of the coving, this will be the front and edges, not the back. Allow the rubber to dry, or speed up the drying process with a heat gun or hair dryer, being careful not to overheat and burn the mould (generally two to four minutes).
Recoat the coving with the rubber moulding five or six times, allowing the latex to dry between each coat. The material will take on a whitish, translucent look. Don't worry about exterior drips.
Reinforce the strength of your mould by moulding in a layer of cheesecloth or gauze. Cover the moulding with the cheesecloth and brush it with the latex, using the brush to poke down any bubbles or wrinkles.
Let the mould dry for 24 hours.
Gently pull the completed rubber mould from the coving, starting at one edge and peeling it back. The mould should pull away cleanly and you will have successfully taken a mould of your coving.
To reproduce your mould, set the mould upside down in a base of loose sand to provide support. Make a mixture of plaster of Paris about the density of pancake batter. Pour the plaster into the mould and let it set for 60 minutes before removing. Your coving is now reproduced.
Don't rush the process. Make sure each layer of latex mould is dry before applying the next. Don't get confused: "moulding" is the British and "moulding" is the American variation of the same word.