I've used a lot of 410 over the years and not had a problem with paint solvents, but have to say that I've not used every type of paint going over the stuff. I know that the mix of 105/205 resin and 410 is perfectly OK with automotive acrylic and cellulose spray paint, both International Perfection and automotive 2 pack polyurethanes and most one pack paints that use toluene or white spirit as the principal solvent. A friend reported that it initially softened very slightly when painted with Polyfiber Polytone, a vinyl-based aircraft paint that uses MEK as a solvent, but that's the only case I've heard of a problem and to be honest I put that down to the MEK softening the epoxy, rather than a problem with 410 itself. Even then the surface hardened back up as the solvent evaporated, with no obvious sign that there had been a problem.
In practice, the 410 is fairly well coated in epoxy when you apply it, especially if just using it as a very thin fairing coat, applied fairly wet with a squeegee. My guess is that West are covering themselves because one or two people have had a paint problem! My advice would be to try a sample with the paint you intend to use and see if it causes a problem.
The only issue I have with 410 is that if it is applied as a stiff mix filler in a fairly thick layer it always traps air bubbles and these manifest themselves as pinholes in the surface. If applied fairly wet as a very thin fairing coat this tends not to be such a big problem, but if the coat is more than just a nafigravit thick I tend to play safe and put a coat of Polyfiber UV Smoothprime over it. This is a water-based urethane primer that fills even the smallest pinholes perfectly, and is compatible with just about any paint finish you want to put on it. The downsides are that it isn't cheap and it takes several days to harden.
Filling larger voids is best done with microballoons and epoxy, just finishing off with a thin skim of 410 over the top. This gets around the problem of air entrapment that makes thicker layers of 410 prone to pinholes to a large degree.
Car filler is not at all good on boats in my experience. The first boat I restored around 25 years or more ago (when I was poor and couldn't afford epoxy!) was faired with body filler and it performed badly. It was OK on areas that weren't immersed, but was very susceptible to swelling and blistering below the water line. I later found out that the polyester resin binder in body filler isn't very resistant to moisture and the filler powder used is talc, which sucks up water like a sponge. The net result is that you get a combination of osmosis and swelling from water absorption of the filler powder, which causes the stuff to blister.
Jeremy
PS: I'm typing this whilst waiting for a new composite prop tunnel to cure, so actually have hands covered in sticky blobs of 105/205 right now..............
