Silicon Rubber Mold Making â€” Part 1

Part 1 of the silicon rubber mold-making reference series. Content is being restored from archive sources.

This series covers:

Selecting a master pattern
Mold-box design and construction
Two-part silicon rubber selection
Pouring technique

See also: the legacy single-page reference at /molding1.htm.

Frequently Asked Questions

What does Part 1 of the silicon rubber mold making series cover? Part 1 covers selecting a master pattern, mold-box design and construction, two-part silicon rubber selection, and preparation of the master before pouring. This foundational phase must be completed correctly before any rubber is mixed, as errors in material selection, mold box sizing, or master preparation cannot be corrected after the pour begins.

What should be considered when selecting a master pattern for silicone mold making? The master pattern must be rigid enough to hold its shape under the weight of liquid rubber, sealed if made of porous materials (foam, unfired clay, unsealed wood), and designed with the parting line in mind — a one-part mold requires a flat back and no undercuts, while a two-part mold is required for anything with significant three-dimensional form on all sides.

What is the minimum clearance required in a mold box around the master? At least 1 inch of clearance on all sides of the master and at least 1 inch minimum depth below the bottom of the master are required to ensure adequate rubber wall thickness. Thin silicone walls (less than 3/4 inch) are prone to tearing during demolding, especially at undercut areas.

Why must masters be sealed before pouring silicone rubber? Porous materials absorb liquid silicone and bond permanently to it, destroying both the mold and the master. Sealing with 2–3 coats of spray lacquer, shellac, or urethane primer prevents absorption. After sealing, a thin coat of mold release (petroleum jelly or Ease Release 200) is applied to ensure the mold can be separated from the master after curing.