Although silicone mold rubber (Mold Max®, OOMOO® and Smooth-Sil®) won't stick to much and has the best release properties of the most common mold making materials used today, it may stick to surfaces with open pores (open grain wood, very dry plaster, concrete, etc.). It will also bond to glass, surfaces coated with shellac and itself (which is an advantage if you need to add new silicone to an already cured silicone mold. (Related FAQ: How do I release silicone from silicone?)
Some tips for sealing a Model Prior to Applying Silicone
- Use an acrylic spray such as Krylon Crystal Clear®.
- Use petroleum jelly thinned with mineral spirits (be careful not to leave brush strokes – rubber will pick them up and they will show on the mold surface.
- Use a wax such as Sonite Wax™ (from Smooth-On) or Butcher's Wax (Home Depot). Again, be careful not to leave brush strokes on the model.
- Use SuperSeal™ (from Smooth-On). Advantage: It is a soap blend that doesn't interfere with surface detail and can be completely removed from the model surface with warm water after use.
- Ease Release® 200 is also effective for releasing silicone rubber from various surfaces.
- Don't wipe model down with alcohol prior to applying silicone rubber.
- Don't Use Shellac! Shellac contains alcohol and the rubber will bond to the model.
- Don't use a release agent that contains silicone (Universal® Mold Release). These types of release agents may act as a bonding primer for silicone rubber. Use only Ease Release® 200.
And, As Always – Don't Risk It. If you have doubts about the compatibility of a sealer and/or release agent with a rubber, do a small test first on a non-critical piece.