View Larger Image Making plaster cavity molds for tile makes it easy to consistently produce tiles of the same design and thickness.

April 7, 2008

Making Multiples: Cavity Molds for Handmade Ceramic Tiles

by Gary Carlos | Read Comments (1)

About a month ago, we ran a feature by Laura Reutter about a surefire method of making flat ceramic tiles (to view this article, see the features archive at www.ceramicartsdaily.org). After we ran the feature, I received some requests for instructions on how to make plaster tile molds, like the molds Laura used in the feature. So today, we bring you a feature on just how to do that. This one comes to us from Gary Carlos. Been dreaming of a custom tile backsplash in your kitchen? These easy instructions can help make it a reality! - Jennifer Harnetty, editor.


If you want to make many tiles of the same design, have a sculptural tile and want to minimize distortion around the edges, or want a consistent tile thickness, you should consider making a cavity mold. To make a cavity mold, make an original tile with the design of your choice out of clay, avoiding undercuts. Make the walls for the mold around a board that measures 1 1/2 inches larger than your tile on all four sides (use laminated wood as this eliminates the need for a mold release). Fasten the boards together with four spring clamps or C-clamps. If the boards are all cut accurately at right angles, the assembled form will keep plaster from leaking without the need to seal the joints with clay. Put a wad of clay on the outside of the base of each wall to keep the form secure. Rub some water on the bottom of your original tile to create a thin slip and stick it to the bottom board allowing a 1 1/2-inch border around all sides.

Pour the plaster at least 1 1/2 inches over the top of the tile – any less and the mold may crack during pressing. For most studio applications, I use #1 Pottery Plaster. Make sure the plaster is fresh (stored for no more than 6 months) and completely free of moisture. Measure room-temperature water and plaster by weight in a ratio of 0.7 parts water to 1 part plaster. Use 1 lb water to 1.4 lb plaster for a 4 1/2-inch square mold and 2.1 lb water to 3 lb plaster for a 6 2/3-inch square mold. Note: I’ve used decimals not ounces.
Slowly sift the plaster into the water. Once all the plaster is in, allow it to soak (slake) for one minute without any agitation. Mix the plaster with a clean stick until it becomes a heavy cream consistency (a milkshake consistency is too thick). This should ideally take 2 to 3 minutes, but can happen anywhere from 1 to 5 minutes.

When the plaster has reached a proper consistency, pour it into the form in a slow steady stream. Shake the table (but not too much) to bring any air bubbles to the surface, and to settle the plaster out, making the top completely flat. Swirl some water in the dirty mixing container immediately and dump it into a waste bucket (never down the drain!). When plaster sets, it gives off heat. After about 30 minutes it will cool back down and you can then take the form apart. If the boards stick give them a quick tap away from the mold and they will pop off.

To use the mold, cut a slab of clay the same size as the opening. Cover the clay with canvas and use a rubber mallet and a block of wood to press the clay into the mold. Use a wire cutter to slice off the excess clay. This homemade wire tool shown is based on one used at Moravian Pottery and Tile Works (where I had attended a workshop). Use a wooden straight edge to scrape off and level the back of the tile. You may want to sign or stamp the back at this point. Give the clay some time to set. This may vary greatly depending on the weather and dampness of the mold. After the clay has set up to about leather hard, you should be able to easily pop it out of the mold.

For expanded versions of this article (and “Flat Tiles the Easy Way,” by Laura Ruetter), be sure to check out Extruder, Mold and Tile: Forming Techniques, from the Ceramic Arts Handbook Series, on sale in the Ceramic Arts Daily Bookstore.

To see images of Gary Carlos’ work, visit www.garycarlos.com.