looking for a fileting material in a pinch.

According to what you are saying, Bondo Hair would be a great pre made fileting material. Only problem is it contains wax, but I guess that isn't a huge issue as I can wipe it down with acetone after it surface cures and then sand it down then glass over it with roven.

 

I found the cake (wheat) flour sands really well once set, and shapes very well. Very easy to mix, just keep adding after the expoxy is mixed until you get the right consistency - from syrup to the thick peanut butter. I also used it for fairing the hull before adding a final layer of cloth.

I found some of the other fillers to be very messy to work with, uncertain of the health of the dusty particles, and quite pricey.

Oddly enough I have read somewhere that structuring flour is ok (I see PAR repeats this in his post here by saying it is medium strength). I think this is to do with flour being fairly fibrous, possibly more so than some fine saw dusts - but shout if I am repeating herecies. I tested some on samples and found it wasn't too bad on its own. (Keep in mind I also later cover the fillets in cloth - so it is not structurally critical.)

 

Cooking flour alone is pretty good, but not nearly as good as other materials. Now, if you mix a high concentration of flour, but use silica to stiffen the mix (control viscosity), and especially if mixed with milled fiber too, it becomes pretty darn tough. You're correct Anthony, it's the fibrous nature of the flour that makes it work well. All the tough materials used will be fibrous in nature.

 

When gutting a 1965 Ensign for rebuild, I kept seeing purple powder when grinding down the fillets that were left after the rotten wood came out. I was later told that Pearson used purple carpenter's chalk to thicken the polyester resin. Not sure how strong it was as far as construction goes, but it was fairly tough to grind down and made an awful mess!

 

The baby powder idea that PAR suggests for cosmetic fillets really does work well. I've found by experimenting that I can stiffen up an epoxy paste with 1/2 q-cells and 1/2 baby powder almost enough that it stays put on a vertical surface (and is fine on anything approaching horizontal). You might need just a bit of silica on verticals.

I wonder, if a fibrous material makes a stronger fillet how about mixing up some resin with Metamucil?

The sugar free kind of course. It tends to "tighten up" my digestive system. Maybe it would make for a easy sanding thixotropic filler?

I'll let you know after I mix up a little batch this weekend.

 

Maybe it will even make the boat "go" faster.

 

Midcap,

I was just encouraging the OP to keep making progress.
Nothing clever

 

I like whole wheat flour and silica.

Dino

 

You can sift sawdust through a flour sieve to make passable wood flour. A little silica smooths the consistency from it being not fine enough.

Dino

 

no problem, I thought I missed something.

 

If you look at all these filler materials through a microscope, you'll quickly see why some are much better at some things and not others. The really fibrous materials have a lot more surface area, so the goo has much more "grip" on these types of materials. Conversely, smooth surface materials , like Q-cells or spheres have quite limited surface area, which is why they're light and easy to sand.

 

The latter two are hollow, meaning there's nothing to sand as soon as you break through their walls.

 

Not to mention fill with goo . . .

 

Sure, but they don't fill with goo until you put the next coat on (after sanding).

 

Yes, but only the broken ones on the surface. Actually, the spheres can't fill with goo, even if broken. Surface tension of the goo and the physical size of the molecules, make this imposable in room temperature cured epoxies.