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Sunday, August 25, 2013

Silicone Mold Release Agents -

*The writer of this site uses a homemade silicon & the below mentioned Krylon Acrylic spray (ie: for fabric & porous non edible applications) or the diluted Vaseline when more practical Am considering trying the below mentioned SuperSeal™.

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.

 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’ll 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

How to Release Silicone from Silicone:

To release silicone rubber from silicone rubber, use a release agent that does not contain a significant amount of silicone oil.

Mann’s Ease Release® 200 was made especially for releasing silicone rubber from silicone rubber and other surfaces. It goes on as a light mist coating and will not interfere with surface detail.

Option: you can also use petroleum jelly thinned with a solvent such as mineral spirits. Make sure you don’t leave brush strokes on the cured rubber’s surface as they will be reflected in the mold

NOTE: Uncured polymer is PVA based - cured Polymer must use release agent

 Why didn't my mold rubber cure?
 A: This is called "cure inhibition"  Cure inhibition occurs when a surface contaminate prevents a material from curing as expected.
Experiencing Inhibition When Making A Mold – When making a mold, cure inhibition occurs when contaminants on a model surface prevent the liquid mold rubber from properly curing. While the cured rubber mold may look fine, you will discover that inhibition occurred at the interface between the rubber and the model’s surface. The rubber will be sticky and not fully cured.

For example, applying latex, urethane or silicone rubber directly over a model made of clay containing sulfur will result in cure inhibition. The sulfur in the clay is preventing the rubber from curing. The rubber may appear fine on the outside, but anywhere the rubber touched the clay, it is sticky and will never cure.
Remedy: Apply a suitable sealer.

Not Allowing A Sealing Agent To Dry or time to “flash off” prior to applying release agent or mixing and applying mold rubber over your model.
Remedy: After applying the required number of coats, let your sealing agent dry thoroughly (30 minutes should be enough) before applying release agent (if necessary) or mold rubber.
Be aware; Humidity will affect the evaporation rate of solvents. The more humid the environment, the longer a sealer or sealer / release combination will take to dry. In more humid environments (80% RH), these solvents can take a couple of days to dry or may never dry depending on the solvent.
Also, if you use a solvent based sealer such as shellac or acrylic and then use a liquid release agent over the top of that, the solvent in the liquid release may "re-liquify" the shellac or acrylic and additional time is necessary to let everything dry.

Applying Rubber Into/Over Rubber - Some mold rubbers are not compatible with others. For example, condensation cure silicones will not cure when applied against an addition cure silicone, and vice-versa.

Minimizing Cure Inhibition – Read the technical data sheet for the products you are using. It should tell you under what circumstances inhibition would occur and what you can do to prevent it. For example, applying a sealing agent to a sulfur clay model before applying mold rubber will prevent cure inhibition in most cases.

FAIR USE STATEMENT: This website article may contain copyrighted material the use of which has not been specifically authorized by the copyright owner. This material is being made available for the purpose of education, commentary and criticism, it is being distributed without profit, and is believed to be "fair use" in accordance with Title 17 U.S.C. Section 107.

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