Thickened epoxy

I'm just getting ready to build my first boat, the Pocket Ship. In studing the plans I am a little confused. In some areas the instruction is to glue parts together with thickened epoxy, lilke the scarf joints. I understand the fillets are thickened with wood flour and to the consistencey of peanut butter. But when glueing scarf joints I would think the epoxy should be thinner. Is it just enough so it doesn't run out?  And if it is thickened at all what product is the best?

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RE: Thickened epoxy

Turn thy PocketShip hymnal to Page 9, "Marine Epoxy Basics."

Last paragraph, Page 9:

"Clamping Glued Joints

For clamped wood-to-wood joints like scarfs, we need the strongest possible mix. We mix colloidal silica powder [these days, usually Cell-o-fill] into the epoxy to thicken it. Silica powder is very dense; it’s literally very fine sand. This mixture produces an extremely hard adhesive. It’s no fun to sand so clean up carefully. We refer to the ideal thickness of such a mix as a “mustard” consistency. It doesn’t drip off a stick, but it spreads easily and smoothly."

First paragraph, Page 10:

"Filling and Fairing

For filling gaps, or for epoxy “fillets” (pronounced “fill-it” in this application), we use low density thickener. The most common material is wood flour, which is nothing more complicated than refined sawdust. You will mix it with the resin and hardener to create a peanut butter-like paste, and you’ll be using gobs of it in the PocketShip. Wood flour and epoxy creates a strong filler which adheres to the wood on either side of a joint, fills gaps well, and can be spread smoothly with simple filleting tools."

The manual is usually specific about the epoxy mix at each major step.  Just pulling at random, bottom of Page 26:

"Mix up epoxy, thickened to a paste consistency, and slather it generously onto the blocking. Clamp the blocking to one half of the centerboard trunk. Use lots of clamps, and clean up the squeezed-out epoxy."

RE: Thickened epoxy

   Also, Hungry, don't breath the silica or Cell-o-fill. You will find that sillica and Cell-o-fill will float around in the air even when you can't detect a breeze so wear your dust mask.  

RE: Thickened epoxy

Here's what MAS says about Cell-o-fill:

Cell-o-fill is derived from all natural alpha cellulose, the fibrous ribbons create a matrix with the epoxy and help reduce sagging and slumping. Used in place of Colloidal Silica, it will not billow in the air like silica and you will need half as much to create the same thickness. There are no health hazards associated with Cell-O-Fill and International standards consider it a nuisance dust.

Breathing protection is still required.  After all, you're still sanding epoxy.

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