Fillers......Decisions, Decisions?????

[Lowell Bernhardt]

While I was perusing the Fiberglass Coatings Inc. website today, making out my wish list I noticed something. Man there are alot of different fillers for epoxy! My question is this: which do you think best for stitch and glue construction? I plan on building Bolger's Diablo and H. Payson just says that I'll need 5# of fillite mix. (boy ani't that helpful!) "Fillite Mix", to me that's kind of like telling someone to go to the drug store and buy "some" pills. tongue.gif
FGCI sells a bunch of different fillers but I really have no idea which to buy for this purpose. I read somewhere that someone used chopped glass as a filler for the fillets on this boat. The stuff seems to be cheap enough, any suggestions? Thanks.

Lowell

[Don Maurer]

I use wood flour (very fine sawdust) and cabosil (Silica fibers) in about a 50-50 mix for everything. The ratio doesn't seem to be all that critical. Mix to a mayonaise consistency for gluing and stiff enough so it won't drip for fillets. Some peaple say a peanut butter consistency, but it never feels like peanut butter to me.

[JimConlin]

Most of these additives and fillers do something better than the others. Here's my practice:

For fairing and cosmetic filleting, phenolic microballoons(like WEST 407) and quartz microspheres both work well. They're easy to sand if the resin mix isn't too rick. A little cabosil makes the bog smoother but harder to sand.

For fine fairing of large surfaces, the WEST 410 is good, but not if the surface will get hot.

For bonding reasonably tight joints, flocked cotton fiber (like WEST 403) thickens the resin so it runs less but doesn't prevent squeezing the joint tight. The aircraft people call this stuff 'flox'.

For structural putty, wood flour is good. A bit of colloidal silica (Cabosil) makes the mix spread more smoothly. It's tough to sand.

For potting fasteners, I use the WEST #403 high-strength stuff. It's miserable to sand. I can't think of another use for it.

These are the fillers I use regularly. There are others, but they're more specialized.
Jim

[Mark Van]

The Diablo doesn't require large fillets, just enough so the fiberglass tape goes on smoothly. I'd just use coloidal silica for that. It is very hard to sand, but if you put the fiberglass tape on before the fillet cures, you don't have to sand it.
Talc is good for final finishing over fiberglass cloth, spread it on with a trowel, and sand. It is pretty easy to sand. I've used quite a variety of WEST system fillers, but I think talc works best.
I've built a 12 foot stitch and glue boat and a 39 foot plywood houseboat, and colloidal silica and talc were the only fillers I used.
By the way, I used Fiberglass Coatings 1 to 1 laminating epoxy resin, and was very pleased with it.
Mark

[Lowell Bernhardt]

Colodial silica seems to be the way to go. What about colodial silica and some chopped glass? I would think that this would make the joint stronger? Just me thinking out loud.

Thanks
Lowell

[Tomcat]

For filleting, I use 1 part sillica and 3 parts Q-cell, or phenolic microballons if the budget allows. I will also use wood flour if it is necesary to have a woodie look.

Keep in mind:

Color: Q-cell is white, Phenolic is purple/brown, flour is wood brown.

Yield: if you use a mix like 50-50 sillica/wood flour you will get at best 1/3 the volume you would get with Q-cells, that means more mixing, and weight, and no structural improvement.

Weight: same as above.

Strength. Don't add stuff like coton, or milled glass unless the joint is going to come under tension, and it isn't being covered with glass (why? not on my boat). Coves in areas like bulkheads where the hull skins and deck maintain dimensions, may not require tension stuff in the form of either milled glass of cloth. For instance on my trimaran hulls only the connectives' bulkheads required glass. On an open undecked boat, usualy the joints will be coved/glassed inside and out, so no fibers are required. The stuff is so forgiving, it is hard to go wrong.