What i'm asking is after i've epoxied the outside of the boat and I want to dill a seam or indention can I use the bondo, then paint over it and that work? Or do I need to epoxy over that again?
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Bondo is a polyester resin and is not compatible with most non-polyester resins. Most boat epoxies (West System, System One, etc) are not polyester resin. System One makes a resin that is compatible with bondo and regular epoxy, but I have not used it. My understanding is that they will not bond well together. Someone please correct me if I am wrong as I have also considered this option.
If you are exposing any wood then I'd re-epoxy it. The bondo will not seal the wood from water like the epoxy.
Also, the bondo will have trouble bonding directly to the epoxy due to the polyester compounds in the bondo. What does work is to laydown your first coat of primer over your epoxied surface then apply the bondo (assuming its just something small) over that primer coat. Fair out the bondo then laydown your other primer layers.
I've never actually used the bondo brand but I have used other autobody fillers as described above. Love how it works!
Thanks bro. Doing some research and your idea sounds good. If I can keep it from contacting the epoxy and then make sure that it's away from the water (painted) I think i'll be ok. The area is WAY above the water line.
When building with epoxy, as most of us do, it is very easy to mix your own "putty" by adding various fillers to what ever epoxy you are using. Wood flour. micro balloons, silica, etc are all thickening agents that work for various different applications. IMO this works best as there is no question about compatability and you can make it as thick or thin as you like. It is a very simple way to create custom "putty".
Well, i'm a knifemaker and have an incredible amount of very fine wood dust in my dust collector (it's seperate from the steel dust before someone asks) and I read where you can make a puddy out of that that will work better than Bondo!! Gonna try!
Steven, Yes, that's basically wood flour. As AJ said, that stuff works real well as a thickener and solves the bondo/ non- adhesion problem as well. I've even put finish "skim" coats of the thickened epoxy on the hull using a 12" spackle blade - it works real nice; much like finishing drywall, you get a real glassy surface and eliminate any overly thick spots. Cuts down on the finish sanding.
Ok, so let's say i've gotten through laying down the fiberglass/epoxy and I have some visible groves where the plywood meets. I can mix up some of this flour into a paste, spackle it on like drywall mud (which I have a lot of experience with unfortunately) and then sand to smooth?
The wood flour putty is a bit tough to sand. It will be smooth but you better have some time and a good sander. You'll save a substantial amount of time and elbow grease if you use a fairing compound like microballoons, etc... I've used Raka's Phenolic Microballoons and West's Microlite and loved 'em both.