I built a 32 foot cabin cruiser boat several years ago with my father and I bought a book on fiberglassing. I was buying resin in 10 gallon buckets and 12 oz cloth in 50 yard rolls! So I've laid alot of cloth and resin in my time. Anyway, the book stated its better to fill the weave with just plain resin, rather than bondo or somethin else, because the resin will soak back into the cloth and create a stronger bond, and bondo just stick to where you put it, it doesn't soak in and penetrate like using resin will.

It works for me.

Jason