Slump Hump Mold Information | Big Ceramic Store


  1. Smooth the slab on both sides.

  2. Cut the slab to the right size and shape. It can be helpful to use a template.

  3. Position the slab over or in the mold.

  4. Define the angles, sides and rim with a rubber rib and a sponge.

  5. Finish the rim with a bevel tool, or as you wish. You might add an extruded rim.

  6. Add handles if desired.

Soften any sharp edges of your plaster mold with a fettling knife.

As a general rule, increase the thickness of your slabs as the mold size increases.

A textured slab can add interest to your finished piece. Experiment with such things as heavily embossed wallpaper, lace, rubber mats, or gunnysack.

If form pulls up in center while drying, slow down the drying by covering with plastic.


While it is obvious how to change the depth of the Hump side of the mold (add more or less plaster), it is not so obvious with the Slump side. The answer is to do two pours.

  1. Coat the mold with mold soap.

  2. Pour plaster into the mold to the level you desire. (This will go into the "ring" or "foot" of the slump mold, and will fill the depth that you don't want. For example, if you want the mold to be half the maximum height, fill half the "foot" of the mold with plaster.)

  3. Shake mold to level plaster. Let set up.

  4. Coat this plaster three times with mold soap, letting the soap dry between coats.

  5. Fill mold to the top with plaster.

  6. Separate the two plaster forms. You will throw away the first pour, and be left with the second pour which is less deep than a completely filled mold.

Another way is to put clay in the "foot" of the mold, smooth with a rib on a banding wheel, and pour the plaster.


Hump Molds: You can use clay to fill part of the mold, then pour the plaster around the clay. For example you could use clay to block out the corners. Or stick clay coils to the bottom in a design, which will be molded into the plaster when poured.

Slump Molds: You may want to change the contour of the wall. Here is a series of steps used to modify an Oval Slump mold by reducing the depth of the wall and changing its contour.

  • Extrude a coil. You can make do with a round coil flattened while turning on a banding wheel, but ideally you will want to extrude a triangle shaped coil.

  • Insert the coil into the "foot" of the mold. Place the coil where the wall joins the floor and smooth it into place with a rubber rib while turning on a banding wheel. Shape this clay into the profile you want your final mold. For example a greater angle to the outside wall.

  • Spray or brush on a mold release. Make sure the mold is on a level surface and then pour in the plaster to the desired depth. The new walls will follow the contour of the clay you placed in the mold, and will be reduced in depth by the thickness of the clay.