What I have done in the past is just to let it run. When all the fill coats are done, then I sand off the runs in one pass. The trick for me is to get enough in the fill coats that I dont sand back into the glass.

> I kept putting on fill coats of resin with a brush and as spidey said, I
> kept picking out brush hairs. I tried the foam brush, but it would flake
> off small bits of foam. Anyway, every coat I'd put on would run or sag.
> I'd scrape it off, sand the whole thing down and then put on another coat
> that would run, sag, etc.

> After getting tired of this I decided to try something else. I sanded down
> an area of the kayak so there were no runs, sags, or low spots. I don't
> want the kayak to look sanded the entire time I'm working on it until I
> get it varnished, so I mixed up a small batch of epoxy and rubbed it on
> with a clean cloth. I used a terry cloth, but a plain cotton cloth should
> work better. I was able to put on a REAL THIN coat without the runs etc. I
> will actually have to put on a couple of these coats if I want to build it
> up.

> My idea is this, why not build up 3 coats with a brush, then clean off any
> unavoidable runs and sand it down. Put on any future filling with a cloth
> and avoid having to sand it all down again. At least it would only be
> light sanding.

> Has anyone else tried this and if so how did it work for you?