I have always used thin coats and a sqeegee in the past for filler coats often toped off by a brush and runs will form up to several hours later. This is with very thin coats. Before I used the Cab-O-Sil method, I put on 3 thin filler coats, each time getting gross runs on the vertical surfaces. It seamed like a lot of extra sanding that wasn't really necessary. My theory is there is always a better way.....just need to find it.

I read somewhere that using Cab-O-sil will prevent runs and hold the epoxy on a vertical edge. It did do that very well. I also thought I read on this board about using Cab-O-sil for the same purpose. I have also read about the amount you can add without affecting the structural properties of epoxy. I think that was 5% by mass so I'm way, way lighter than that taking 1/12 by volume. Effectivly, to coat the entire hull and sides using a roller, I used a total of 4 tablespoons of the stuff. So I'm not worried about structural effects.

Also this time I used a thin foam roller from West Systems. I think some of the milkyness also came from using the roller compared to using the sqeegee.

Except for the hard little points, which scraped off, I am pleased at how it prevented runs as I was able to put on a thicker coat than before with no runs at all.

Cab-O-sil is fused silica, I think that some are confusing this with micro balloons, which will color the epoxy white.

I guess my next stage of experimentation will be to brush as Nick suggests. Doesn't this introduce air into the epoxy from working it so much? Also, do you use a foam brush for the fill coats? How wide of a brush?

Thanks for the input. I'll post a pic later this week of the Cab-O-Siled hull and using a scaper for those who are following this.

Tom

: I don't recommend the cab-o-sil to thicken the epoxy. Like Lee said, it will
: dull the finish and make sanding more difficult.

: Instead, use the same brushing pattern I use for varnish. Working from
: centerline to sheer line in about 1 foot wide sections: With a full brush
: spread on the epoxy using horizontal strokes (parallel to the centerline).
: Without refilling the brush, even it out with vertical strokes (center to
: sheer line). Then one more time with a lighter touch tip it off with
: horizontal strokes. Move on the next section. (If I were varnishing, I
: would alternate sides to maintain a wet edge.)

: The key to avoiding drips and sags is getting the coat even and smooth. If
: you are careful you can actually end up applying quite a bit of resin in
: one coat.