I have two friends who have opposite ideas as to the order for filler. I have always sanded the piece to bare metal then sprayed a coat of self etching primer then applied any filler needed and then sprayed sandable primer and then finish sanded. Friend says this is a** backwards that I should sand to bare metal then fill any dings with filler and then spray the etching primer. Then the sandable over that. Any ideas as to which is better or does it make a difference? Mike +++++++++++++++++++++++++++ If you read most body filler containers most say to bare metal. There are fillers made to go over primers but they are finish fillers, mostly finer polester fillers than the others. There are now more styles of body fillers available than carter has peanuts. Some fillers are made for quick sanding and finish work, others made that are much smoother but require a lot more sanding. One line of fillers available are specifically formulated for BC/CC paints and not recommended for single stage. Ditzler's DP series epoxy primers were made for under filler work. I owuld just follow the directions on each filler can. If it says, bare metal, then bare metal it is. ++++++++++++++++++++++++++++++++++++ The filler is to smooth the body panel and should be applied on bare metal so that it can bond to the sanding scratches in the metal. The bondo should not be greater than 1/8" thick. If it is going to be thicker than that you need to do some more metal work. Then comes the self etching primer. Derrick +++++++++++++++++++++++++++++++++++++++ Well, if you use an epoxy primer like Ditzler DP40, it's better to apply it first, and the filler over top. The epoxy primer bonds better to steel than does polyester filler, which in turn bonds better to the primer than it does to steel. At least this is what I was told by a pro bodyman who used Ditzler products. It works for me. Gordon Richmond +++++++++++++++++++++++++ Old way--bare metal then filler, then primer. The last 10 or so years, bare metal --epoxy primer, then filler with fill primer on top of that. Keep filler to minimum thickness. Gorden is right! Epoxy primer sticks better to metal than filler, filler stick better to epoxy primer. Kerry ++++++++++++++++++++++ Just a small addendum to this... NEVER put bodyfiller directly on bare metal- ESPECIALLY if there are any pinholes, seams, etc in the surface. Polyester Fillers will ABSORB moisture if the surface is ever broken. So, if you get a scratch-through to the filler, it will absorb moisture from the air and directly transfer it to the surface of the bare metal... guess what happens? Rust occurs between the metal and filler, and eventually it delaminates from the surface. Whenever I treat bare metal (usually freshly sandblasted)... it is ALWAYS with an epoxy primer. It has great adhesion properties to bare metal, and is commonly used as an "adhesion promoter". Self-Etching primers are good, but they are applied relatively thin... and do not hold up well to age without a topcoat (this is fine for "collision" work where the repair is done in short period of time). But, this is a hinderance if you store the pieces for long periods of time before getting around to working on them. Even so--- IF the primed pieces sit more than 72 hours---- I scuff the epoxy primer with 80 grit and reprime before I apply any fillers or high-build primers. Even after fillers and blocksanding- I reprime any areas that were broken to bare metal with epoxy primer again. Then of course- an epoxy "sealer" is used just before application of the finish-coat. When done in this fashion, even if the surface is ever broken and the filler absorbs moisture- it cannot transfer to the bare metal due to the epoxy barrier coating. If the moisture cannot get to the surface (steel) therefore no oxidation (ferrous oxide) can occur. I used (PPG not Ditzler) DP- systems (DP- 40 green, DP-50 white, DP-90 black,...etc) for years until it's recent re-formulation. It is/was excellent primer. I could prime a sandblasted piece and leave it outside a few months before any evidence of oxidation would occur. This was due to the primer breakdown from exposure to sunlight. Most primers are suceptible to UV and other damaging sunlight. To conclude: bare metal, epoxy primer, filler, epoxy primer, high-build primer, final "blocking", epoxy prime any filler or bare metal areas, epoxy sealer, finish coats Ray ++++++++++++++++++ Waterproof fillers..- Yes there are, but be careful, the only true 'waterproof' fillers are those that have fiberglass in them, and one made by USC called All-Metal. With fiberglass fillers like Gorilla Hair and Duraglas, only use the thinest possible amount, and never bring it higher thant the dent. Only use it to fill small holes, and I mean small, and if the holes are bigger than a pencil eraser, make sure that you flatten out the filler on both sides of the repair. Then apply an epoxy primer on the inside of the repair and then topcoat with some paint. Use a really good filler on top of the waterproof stuff to get a smooth finish. If you bring fiberglass filler higher than the repair, you will spend a whole day trying to snad it down. ++++++++++++++++++++++ If you do not have large areas that need a filler and you are not into lead, then useJB Weld or something similar as a seam filler over bare metal. Or epoxy primer, epoxy filler, epoxy primer with acrylic lacquer thinner as a sealer (per DP-XX instructions). The only primers that I have seen hold up as well are the old style enamel primers. Paul Villforth ++++++++++++++++++++++++++++