It has been our experience that plastics poured into or over plaster molds may give unsatisfactory results. However, we also find that because of size, the economies of plaster are inescapable. We therefore recommend that when plaster must be used (use Ultracal 30 only) it's well worth the trouble to make a plastic-faced plaster to eliminate many of the drawbacks plaster has as a molding material.

When plastic-faced plasters are used,the porous surface is eliminated, making releasing easier. Also, sealing is no longer required and the hard surface is easily sanded.

To begin the construction of a plastic-faced plaster, prepare and release pattern with adequate parting agents. H.B.Fuller or Hapcoat 3750 is the recommended epoxy surface coat to be used for plastic-faced plasters.

Mix H.B.Fuller or Hapcoat 3750 according to directions and apply the first coat sparingly with a stiff brush, concentrating on dabbing at inside corners to insure air does not become entrapped at these points. If you keep this first coat think you can see any air pockets that are created by brushing. Dabbing or stippling gives better results.

Allow this coat to gel to a state called "tack-free" (this means the plastic is still soft, but does not stick to your finger when touched). At this point, mix and apply a second surface coat. This can be applied more liberally and with less care than the first coat. Immediately upon completion of the second coat, pour plaster into cavity, completely filling void. Allow to set 8-12 hours.

Note: Before pouring plaster, many customers arrange sisal fibers around cavity into wet surface coat. This gives plaster and plastic a mechanical bond, as the chemical bond is never as good a plastic to plastic. This is optional and is necessary only if the tool will be reused often or is to expected maintain dimension over a long period of time.
NOTE: Mandatory and recommended industrial hygiene and safety procedures should always be used when handling materials.