While silicone mold rubber generally has excellent release properties and won’t stick to most surfaces, it may adhere to materials with open pores (such as open grain wood, very dry plaster, concrete, etc.). It can also bond to glass, surfaces coated with shellac, and itself (which can be advantageous when adding new silicone to a cured mold).
Here are some tips for sealing a model before applying silicone:
- Use an acrylic spray.
- Use petroleum jelly thinned with mineral spirits, being careful to avoid leaving brush strokes as the rubber will pick them up and they will be visible on the mold surface.
- Use wax, again being careful to avoid leaving brush strokes on the model.
- Avoid wiping the model with alcohol before applying silicone rubber.
- Do not use shellac, as it contains alcohol and the rubber will bond to the model.
- Avoid using a release agent containing silicone, as it may act as a bonding primer for silicone rubber.
As always, it’s important to err on the side of caution. If there are doubts about the compatibility of a sealer or release agent with the rubber, it’s best to conduct a small test on a non-critical piece first.
