Tips and Tools: Protecting Plaster Molds

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Rachel K. Garceau’s Within the Hollows, slip-cast porcelain. Garceau uses plaster molds to create slip-cast forms for her site-specific installations.

Have you ever noticed gouge marks on your plaster molds caused by strap clamps? Try recycling old yoga mats to protect your molds.

As we all know, plaster is a contaminant to clay, so working with plaster molds requires careful handling and attention. This is particularly important when using multiple-part molds, which are usually held together with mold straps that have a metal buckle. When tightening and loosening the strap, the buckle can gouge the plaster, wearing away the outside of the mold and increasing the risk of plaster bits getting into your casting slip or clay (1).

1 Damage on the outside of a mold caused by the buckle on the mold strap. 2 Use scissors to cut up old yoga mats to use as protection between your plaster molds and the mold straps.

Cushioning the Clamps

In order to protect my molds and decrease the potential for contamination, I cut up old, worn out yoga mats (2) and place them between the mold and the buckle on band clamps before securing the clamp (3). Not only is it a great way to recycle my old mats, but it’s also a great material to put between a mold strap and a mold for several reasons. The mats are thin, so they don’t add bulk to the outside of the mold, which can get in the way while using and storing the molds. The mats have a surface texture that is spongy and grippy, so they prevent the strap from slipping and give you a little extra play for clamping down on the strap. Lastly, if the mats get casting slip or clay on them, they are easy to clean with a sponge and water and dry fast.

Rounding the Edges

Another precaution I take during the mold-making process is rounding the outside edges of the mold (4). This helps to reduce the possibility of chipping a sharp corner. I use a Surform rasp followed by sanding using wet/dry sand paper under water to avoid creating dust. This process also creates a small groove between mold pieces which can be helpful when taking them apart and putting them together.

3 Place the cut yoga mat pieces underneath the mold strap’s metal buckle when securing the mold for slip casting or storage.
4 Round the edges on mold sections to further prevent plaster from chipping off.

Composting Plaster

Tip: Plaster scraps and old molds can be broken down and mixed in to compost, providing a source of calcium to the soil. Interestingly, if you have heavy clay soil, the gypsum (plaster) can help to break it up.

the author Rachel K. Garceau is currently living and working in Atlanta, Georgia. Garceau has completed artists residencies and fellowship programs at Penland School of Crafts, North Carolina, Vendyssel Kuntmuseum, Denmark, and Arrowmont School of Arts and Crafts, Tennessee. To learn more, visit


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