I'm old school from the days of using lacquer primer, etc. We used to 60-80 grit the metal, apply bondo, sand and then primer. What's preferred way now with 2k urethane primers? Some say: metal, bondo, primer. Others say: metal, primer, bondo, primer again. I'm restoring a '56 Ford oval track racer. I've replaced rusty body portions with new sheetmetal. Much of the old car had surface rust when it was built years ago and was sanded and then primed with some sort of thick high build gray primer. Except for where I'm doing bodywork, the primer adherence is fantastic. It was painted red over this primer and I've stripped that top coat off with razor blades. Naturally, where I'm body working it's to bare metal. I'll probably be using Southern Urethane primers. I have a bunch of Northwest Airlines airplane paint kits that I'll be using for a top coat.
Bondo should NEVER be on top of anything but 32-grit prepped bare metal, if you want it to stick and last. You can, however, use glazing putty on top of primer sanded with 80-grit. Hope this helps!
Nothing has changed since old school only the technology in the products My weekly metal work blog www.themetalsurgeon.com
I just shot these photo's this week to remind myself why I chose METAL-PRIMER-FILLER (hint: the dark spot in the middle) They're from a 58 GMC grill I'm working on. I know it sat from the 80's to 2009 under a tarp in Camp Nelson, Ca which is about 4500' El, so it saw annual freeze/thaw and snow/sun (ok the sun was in the form of cedar boughs dropping) Though out of focus this was an attempt at showing rust at the bottom of a filler repair. It didn't show until I'd sanded down through what I'd originally thought was straight metal under the paint... Just food for thought. For desert consider the benefit of using SPI epoxy primer to seal the metal before the filler... A shot of a 70's or earlier repair that sat out doors for 20 years. Clearly this held up over many years but it to failed... But, it was also done over the original paint not bare metal so was that being lazy back then or reasoned as is now (apparently) the the thinking regards metal protection?
The body filler is like a sponge to water. The primer is not a sealer. So if a primed car is left to the seasons, most likely there will be rust under the body filler. Glazing putty is that, for light glazing. Even that, the primer has to have some good scratches in it. For example, I was not able to work on my car over winter, it had a supposed water proof cover on it. There was a few spots with exposed metal and light body filler. There was more rust under the body filler then around in the exposed metal. The filler is like a sponge and traps moister. So if you can, Metal, prep the metal with some kind of cleaner etching solution, body fill, self etch prime, then filler primer.
What tha heck are you guys using for body filler? Duraglass (and similar products) is totally waterproof. I never use anything else over bare metal. That light stuff is strictly for filling sanding marks as far as I'm concerned. So my formula would be metal > duraglass > bondo > primer
I use Rage gold or Evercoats Z Grip. The issue is if there are any pin holes, with there will be the water gets right in. I have never been a fan of fiberglass fillers myself.
I'm pretty old school, still use lead (sometimes), but also appreciate the modern technologies for their better adhesion, abrasion and chemical resistance, long lasting shine, etc. To answer your question: You can do it either way. Epoxy primer has better adhesion to metal than bondo does. Any other primer, you probably cannot use under bondo, check the tech sheets for exact info on it. Even if using high build urethane, you need to put an etch, or epoxy primer under it for best adhesion. Different bodymen will give you different preferences, but there are a few ways to do it right, not just one! For example, epoxy over bare, filler work over it, spot in bare spots with epoxy, then high build, then sealer, then paint. Or filler over bare metal, then epoxy for adhesion, then high build, etc. Or etch primer first, remove etch, do filler work (the etch primers I used are not good bases for fillers), then either epoxy, or epoxy then high build. Or you can use House of Kolor primer, it has great adhesion, you can use filler under it, and over it, acts as a high build primer, sands easily, and it acts as a pretty good sealer as well, though they also sell colored sealers, incl. a silver metallic one. The thing is to know the products you are using and use them correctly for a long lasting base for paint. Oh...and a pet peeve is using fiberglass or other waterproof filler over bare metal to "preserve or protect it". If you have pinholes in the metal, water will get in and rust the steel under the filler. Yeah, an absorbent type filler may suck up some of the water and perhaps accelerate the problem, but it is the metal underneath the filler rusting that causes the rust bubbles to appear! Do your metalwork right , no tack welding or stitch welding, or flanges...butt welds, solidly done, and then for extra insurance, a good rust preventative or sealer on the backside of you work. I like POR-15 topped with undercoat or bed-liner.
Bare metal, sanded 80 grit, epoxy (SPI), body filler (Rage Gold), epoxy w/reducer as sealer, base color (House of Kolor), and clear (SPI Universal) works great for me.
Nothing else even comes close to epoxy for protecting the base metal. I bought and rebuilt a 20 ton heavy equipment trailer in the late 80's. Once all the fab work was done, we sandblasted everything, shot it with a Sherwin Williams industrial epoxy primer, and put a coat of S-W industrial enamel over the epoxy. Since then, that trailer has run thousands of highway miles and spent a bunch of time on construction sites where the frame gets bombed with all sorts of gravel, dirt clods, and anything else the tires sling up. Today, there's not a speck of rust anywhere on the frame or underside of the bed. A typical trailer like that one will have significant rusty spots on the underside in less than 10 yrs because a fair amount of the factory primer and paint has been knocked off thru use. If we'd used any sort of primer other than epoxy, ours woulda been ready for more paint probably 15 yrs ago.
Here is what I do, I use PPG products. I clean all metal of rust and make repairs as needed, clean all welds with a wire wheel or similar means. Sand all to bare metal with 80 grit, wax and grease remove. Spray a self etch wash primer first, it is a yellowish color and very thin. Then it is on to DP90 black, the black shows everything. You have up to 7 days to apply filler directly to the DP, but I usually wait a day and scuff it with a red scuffy. The filler bites into the DP in a chemical way and gives better bite than grinding does. My opinion. Sand filler, I use rage gold, up to 180 grit, look for pin holes and fill with a glazing putty. Then once filler work is done it gets another coat of etch primer on the bare metal spots that got exposed because of sanding, one coat of DP90 again, let dry over night. Then I spray on 2 coats of slick sand. I let the slick sand sit for a month before I sand that. Sand slick sand with 240 then 320. Then 3 coats of DAS primer. Then I let the primer sit another month, the waiting is for shrinkage, They say it is sandable the next day but that is bull shit in my experence, if you waited this long a few more months is not going to hurt. Once sanding is completed DBC for color and then some DCU for the clear. If you want numbers for all the products send me a pm.
It doesnt really matter, the bondo will fall out the first time you get hit anyway. Bondo has weight, think "Light is fast". Paint it and race it. You'll never tell the difference from the grandstand at 100 mph. Hope you have fun with your new project.
I use Kirker epoxy. It has the benefit of being iso free. It builds and sands well ( most epoxies do not ) and is only $100 for two sprayable gallons. Epoxy is also the most water resistant primer, so if something is sprayed with epoxy, weather isn't an issue if left sitting.
Things have changed as far as putty goes too. The old stuff won't adhere to epoxy and most of the polyester primers. I use an epoxy primer, then I try to use Evercoat products for the rest of the prep.
Question I have a fender I got back from the media blaster which has some rough body work done to it. He sprayed it with epoxy primer. I am not ready to start all the body work at this time. When I do start how should I rough up the area prior to filler?
Just dont forget to scuff the epoxy before the bondo. I do metal, epoxy, bondo, epoxy, highbuild. Maybe iverkill, but its never failed me -LUKEY-
I guess you don't have much confidence in my driving!!!!!!!!!! If I ride around in the back, I won't be a target!! You'll like it. Come on by and pay me a visit. I still have your cooler here someplace.
The next week or so will be real busy at work, shutdown/maintenance...after that I'll make sure I get over there...I'll try to dig up a pic of our old 56 ford dirt car.Thanks for the invite.
We use House of Kolor KP2CFA/B epoxy over all of our metal work before filler. It is a crazy lime green color when you mix the light blue and yellow a&b parts. The shocking color is so you know where you have put the product. It sucks to spray a grey colored epoxy and forget where you have sprayed. Bare blasted fresh metal and grey epoxy look alot alike in the shadows. Once dry the epoxy is sanded with 80 grit to get filler to stick. Then prime, sand, paint as ususal. We have been using this product for years with great results. Questions? PM me.
I know this is an old thread, but here's my 2 cents. I did a 57 Chevy Belair 2 dr hdtp complete off frame. I decided to try filler over epoxy primer. I used SPI black epoxy primer over the bare body, 2 coats as per instructions, let it sit a day. By the looks of the semi-gloss finish I thought the filler would not feather out properly. However, I found that was not the case. No sanding at all is required if coating is done up to 7 days. The filler feathered great, and the glossy black finish made it easy to see areas needing fill. After blocking another application of epoxy can be used or a build primer. I used all SPI materials from the epoxy to urethane prmer, black base and their universal clear. Not only are their products top notch, the prices are great, $180 for a gallon of epoxy with a gallon of activator. It is a true epoxy mixed 1:1, spray with a 1.3- 1.4 tip. Great products, prices and service.
This is what happens when you use filler over bare metal , had 50 cent sized ding that cracked the filler and this is what was underneath had to take it all out , this was done a long time ago but the car has been garaged an not outside
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