I am going to start working on a cab for my friend and will need to do minor filling on a front fender where it is dented, Do I need to sand to bare metal and epoxy first or can I sand the OEM paint and fill over that? Thank you in advance for your help.
For fixing a small dent try to get the dent out as much as possible. Its best to go down to bare metal, but as long as you feather the paint out with 180 grit or so most fillers will adhere to sanded OEM paints. If you purchase a quality filler it will state on the side of the can what it will stick too.
Depends on what it is and what you and the customers expectations are. Collision type work, I will sand to bare metal and apply the filler over 80 DA sand scratches. Restoration type work I will apply epoxy first (part is usually stripped to metal) and apply epoxy over that. I've never been comfortable applying filler over sanded paint. 2 part glaze i small amounts yes, but filler no.
I am with Chris on this one.....BUT know of a large dealership body shop that has the body men feather their plastic filler into the paint with no bare metal showing or paint edge to feather out if you understand what I am saying. The work they deliver is very GOOD for dealership work.
Usually when doing collision work and repairing a dented fender for example I will usually have no or very little metal actually showing. I'll cover the bare metal, then have the result like you described Toro, but I don't like putting it over sanded paint. Feathered out into the existing finish yes but never over sanded paint. Just the way I have done it. If you were to do it I'd only do it over OEM paint sanded with 80 and never over refinish paint.
Keep in mind that for the highest quality it's always epoxy first then filler, but lots of times that isn't possible, due to the type of job and how much you are getting paid to do it. You've gotta factor that in JC.
My technique is a little complicated to explain, but basically what I have learned is that most (not all) OE finishes will accept filler well, but paint (unlike metal, which should be 80 or coarser) likes a really fine scratch before filler if you don't want it to show down the road. Luckily I own my own shop and don't have to put up with the other bodymen laughing at me for feathering out the paint around my repairs with 220 before filler.
I really appreciate all the help and advice guys, I am going to get as much of the dent out as possible and sand down to bare metal with 80 grit then epoxy and fill the following day. I want this truck to be as good as I can get it.
Do the same thing Crash, but usually with worn 80 or 180 on my aggressive DA. Snap On PS100. I find that probably like you, it's the only way to avoid that halo effect. Most OEM paint now is so thin I just DA the paint off rather than use something rotary. When I do need rotary for getting paint off I just lock the old trusty Snappy. No need to put anything coarser than 80 grit on the metal.