Official Luthiers Forum!

Can anyone describe the visual impact of adding fumed silica to clear epoxy? Any brand differences?
I'm thinking of trying it in my System Three Silver Tip for pore filling/figure popping.

I have used the System Three silica in Clear Coat when the pores are large and even in Seal Lac to help it fill pores. It works fine. You can't tell it it is in the mix once cured. I haven't tried any of the cheaper brands and since I don't use very much there is little incentive to do so.

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Joe Beaver
Maker of Sawdust

I can't speak specifically of West Systems product..:

The fumed silica products I have used in the past tended to give clear epoxy a light milky white/opaque color... But didn't really turn it white...

I have never used it in a finish application - we used it in places where you needed the strength of glass mat but couldn't get a woven product in...

Its also very effective as an additive to reduce sagging/flowing of epoxy...

The stuff is very very fine glass particles... As such - it makes epoxy very very hard to sand and extremely abrasive on edge tools...

Test on scrap. Proceed with caution.

Also has severe health dangers......

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Thanks for the input.
I've run into some conflicting information. Probably due to differences in specific products. That's why I'm asking about what you guys have used and found.

Some say it yellows epoxy a bit. Some say milky others clear.
I found this:https://www.aerosil.com/product/aerosil/en/industries/adhesives-sealants/effects/transparency/pages/default.aspx

MSDS says pretty safe, not associated with silicosis like you'd think. Not that I'd be cavalier about getting anything but clean air in my lungs.

I really like the Silvertip epoxy. I can apply two passes in one day and I don't need to sand between them. It also sands very easily! I think you'll like working with it...

I've never used fumed silica for pore filling. Always for thickening epoxy for leveling fiberglass, or sometimes for fillets at joints in fiberglassing on boats. Thus it tends to be a bit thicker coating and tends to get more milky as you gain depth. As mentioned above, it makes the epoxy very hard and more difficult to sand, so I'd stay away from it for pore filling where I want to sand as lightly as possible in order to get it level, without exposing fresh wood and pores. Always wear a mask with this stuff, though. It blows around with the slightest air movement.

-Tony

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Tony Thatcher
Bozeman, Montana

I often use chopped polyester fiber additive in my West Systems epoxy. It makes it much stronger. The cured epoxy is just the slightest bit more opaque, but really adds no color at all. I don't use the fiber when pore filling, just for structural laminations and glue ups. You can add a little or a lot depending on how thick you want the wet glue. A lot allows you to make fillets in corners.