Q&A: Problems with Silicone Plugs

Q. We have problems with smooth powder coat finishes from what we think is plug contamination. When a silicone masking plug touches the surface of a part, it causes a powder separation similar to a large fish eye. Is this a common problem, and how do we avoid it? Will washing the silicone plugs before they are used help? B.A.

A. There are a few types of powder that do not like silicone in any form (plugs, tape, release liners, etc.).

The common problem with silicone goes back 20 years when masking supply companies used to use a silicone-based (think WD-40) mold release. Most reputable masking material suppliers do not use any mold release other than soap and water, and have not done so for many years. This has enabled them to use silicone as a primary material for its exceptional resistance to the heat requirements associated with the curing of powder.

In the rare instances where a coating completely conflicts with silicone, you should use EPDM masks, which are used by many large companies that have concerns about silicone plugs. The down side of EPDM is its limited reusability. Silicone plugs will provide more cycles. But EPDM can be the right choice when the appearance of the finish is far more critical than the cost of the mask.

It is possible that your supplier uses a mold release that causes the problem. Try another supplier before going to the EPDM. Find suppliers on the Products Finishing website at PFonline.com.