someone told me that i should prime my fenders because they are pitted and then skim a light coat of bondo over it to fill in the pits. my question, is it good to use bondo over primer or better to use it on bare metal.
Fordy8man

Any body guys out there I need the same info, I am just abought to start reparing small bubbles in the paint.

 

First of, I'm not a true "bodyman". I would say that it depends on what brand and type of primer you're using.

I use DP (now DPLF or Lead-Free) 40 primer(PPG/Ditzler's catalyzed prime). With this primer, it is recommended to prime then put any body filler over it.

I've used this primer for over 13 years and never had a problem. The old lacquer based primers you had to do the opposite, filler first then prime.

Hope this help a little.

 

There are two schools of thought on this. As of late, body shops have been primering first with an epoxy primer, then doing body work. Of course if you are repairing a large damaged area, or rust I would repair that first then primer. Usually when a car is primered first the body is fairly straight and only requires surfacing to remove low spots. The old school method still works well of repairing the body defects then primer.

Vince

 

Body filler is nothing more than polyester resin with microspheres or microballoons added to it. That is what makes it "lightweight" and makes it easy to sand. It also makes it porous. If filler stays wet enough, it will actually absorb the water, and hold it against the metal like a sponge. The best way to protect the metal is by using a rock solid epoxy primer first, then subsequent coats of whatever. The epoxy primer will also adhere to the bare metal beter than the filler, making your bodywork more durable.

 

In theory, epoxy first sounds like the way to go . But for 50 years filler first, if applied right has worked perfect for me, why fix something that isn't broken??

Troy

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I was taught to apply body filler over bare ground metal. A few bodyshops I worked at used epoxy primer first and applyed the filler over the epoxy primer. I think either way you want to do it would be fine, but you have to scuff up the epoxy primer before you apply your filler if the epoxy has sat a certain amount of time, I believe its something like a day or two, but not sure of the exact time.

 

Fillers today will stick to most anything. I've bondoed over bare metal, primer, epoxy primer, and never had a problem. I worked on a former taxi cab that had 3 inches of bondo over the paint, dang near had to chisel it out. I wouldn't bondo over paint myelf, but have no qualms about a skim coat over primer. Dan

 

Sounds about right to me, Dinger

 

thanks guys. you've all been good help.
Fordy8man

 

What I do is this.Self etching primer(matrix),Epoxy prime(matrix),Filler(if not using lead) and then a high build primer(like transtar or 5 star).

 

One of the first things you learn doing body work, is to apply the filler to clean metal, that means no paint, primer, rust, just clean metal.

Troy
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69 ss rs full custom camaro 98 ISCA grandchampion
69 ss rs bb camaro wifes driver
66 Elcamino 350/all dz parts,ac,windows,loaded,my driver
69 ss chevelle bb conv.fresh frame off
26 T sedan street rod

 

<---- worked in teh body shop for the last 5 years ... listen up

if you have panels that are starting to rustbuble and such, the VERY BEST way to repair the rust spots is to grind them, sand blast any little craters that are left from the rust ..... use a VERY high quality primer over them like PPG 271/275 .....

then just sand that w. 80 on a DA and bondo over it ..... i SWEAR that bondo will stick to todays high quality primers, just prime over everything again when your done to seal it up

The real reason for the idea that you have to apply bondo to bare metal, THEN prime over it is cause back in the day when body filler was still an undeveloped product that was a PITA to work with, it wouldnt stick to paint and it blead through to the paint, (yellow spotting) so shops would save all the primer for ONTOP to try to seal it real good, but that was only laquer primer ..... which is fawkin worthless too

grind, primer, bondo, sand, bondo, sand, primer, guidcoat, sand, if its as straight as you want ... its ready for paint


good luck man

 

<---- worked in teh body shop for the last 5 years ... listen up

The real reason for the idea that you have to apply bondo to bare metal, THEN prime over it is cause back in the day when body filler was still an undeveloped product that was a PITA to work with, it wouldnt stick to paint

Well I'm glad that I know the REAL reason it was done that way. All of the years I did bodywork only to find out that it was not supposed to last. LowRoller....I hate to say, but some of the fillers they have today are the same fillers they had back when you were still riding the tricycle. Look at the directions on most cans of filler and it states to apply over clean metal. Everyone has a different way of doing things and when it comes to fillers some will apply over primer and some will apply over metal. The cars that we did were did to last for years. Applying over metal worked and if you take a look at the professional restorers, most will go to bare metal. One reason I like going to bare metal is to see what is under there. Especially if it is a car that has previously painted. I'm with Troy on this one.

Kevin

 

heh ... first off id liek to take back some of my drunken phrasing from my last post ... for example that **listen up** ... im not that ****y in real life .... only when ive got a full load in me

ill tyry this again ...

if you have panels that are starting to rustbuble and such,the way i prefere to repair the rust spots is to grind them, sand blast any little craters that are left from the rust and then brush in some high quality primer over the pitted areas... something like PPG 271/275 ..... just to try to hold the rust back for as long as possible, im anal about some stuff ... like my worries about rust coming back

its always best to grind down to bare metal, i agree TOTALY on that, cause you never know whats underneith the old stuff

when i DO primer an entire panel to start w/.... ill go back and sand that w. 80 on a DA and bondo over it ..... two fillers that i have experience using over the ppg 271/275 are the Bondo Brand and Everlite brand, ive seen both stick to the 271 quite well. after bodywork is done just prime over everything again when your done to seal it up

and then just ignore everything i said past this point in the LAST post on here ... lacquer is a good product when used properly ... works GREAT as a filler for perfecting the panel, just make sure you use the proper paints over it to avoid problems. my old boss attempted to use dbu/dbc base and 2002 clear over lacquer primer .... that held on for like 2 months ...

yes, alot of the fillers ARE the same stuff or only slightly different .... i actualy ment more about teh spot fillers (putty) .... THOSE have come a LONG LONG way since the green stuff

hopefully i sound LESS like an ashhole this time .. lol

 

One reason I like going to bare metal is to see what is under there. Especially if it is a car that has previously painted. I'm with Troy on this one.

Thats why I don't like to go to metal sometimes. It sucks when you get a vehicle and end up digging into someone elses bodywork and its 5 inches thick on a panel that was never pulled out, or over big rust holes. I have mostly applyed my filler over metal and haven't seen a problem with it lasting. Even on a car of mine where I applyed it a little thicker then I would of liked to It has been holding up fine. I don't see much change in the bodyfillers from when I started using them 15 years ago, except for more and more fancy terms like space age microspheres. I've also applyed filler over epoxy primer before and it seems to work fine. One thing I've never done is apply it over paint, as I've never heard any of the tech people say to do it that way. Only thing I heard its okay to apply over paint is some of the finishing puttys in a thin coat. The biggest problems with the filler seems to be from people who abuse it. I will agree with you on the lacquer primer. In my opinion the catalyzed urethane primers are a much better product, but already been disagreed with on that, so find out what works for you and use the products the way you like.

 

lowrider, sorry but I feel you dont have a clue!

I assume when you say 271/275 you mean NCP271/270, sorry but NO WHERE in the tech sheet does it say you can topcoat this product with filler. You can apply a poly glaze product to correct minor imperfections but thats a FAR CRY from appling body filler.

Plus NCP primers DO NOTHING to prevent rust that has already started. Again the tech sheets state this fact. READ THEM.

Both methods have a place in the repair world. But if done properly filler over clean bare metal with outlast you and your kids...Eric

 

270 and 271 are the red and grey primers .... and the 275 is the one catalyst we used of the 2 available for the product.

your right ....the psheets read somethink like techni-coat or something like that for filling minor imperfections, but then again ... ppg doesnt make evercoat filler, so i wouldnt expect the p-sheets to list evercoat as a suitable topcoat over the ncp primers

and ive had plenty of chances to see our previouse repairs come back wrecked again ... and the filler seams to stick just as well on damaged, warped panels weather its applied straight to steel or over primer, even when i had to beat on wrecked hoods to get them open ... it didnt flake off right away ... so with the same prep i would expect it to stick juuust fine to a panel that doesnt flex or wind up damaged somehow

as far as ncp primers preventing rust .... ive got some real cheap as can be epoxy ""corrosion resistant" primer on the hood of my lebaron .... JUST primer ... and i managed to rip the primer off the front edge one day by mistake ... just drove it through a salty new york state winter ... rust spot didnt get any bigger ... and the same primer is holding down the rust spots in the center of the hood that i blasted real well .... even though the primer is literaly thin enough to see through ... i think maybe ..... juuuust maybe if the $75 gallon of cheap stuff can seal up that rust .... ncp can do an even better job when used the same way

 

I made the mistake of hitting a quarter size rust spot on a 66 SS chevelle hood with a spot blaster once, wow, I'll never do that again. It took three days to get it back straight.

I use bondo-cote mastic/polyester glazing putty over primer, but never over paint. Can't find on the can that you can use it over paint.

Troy
__________________
If you don't make mistakes. your not doing anything.

69 ss rs full custom camaro 98 ISCA grandchampion
69 ss rs bb camaro wifes driver
66 Elcamino 350/all dz parts,ac,windows,loaded,my driver
69 ss chevelle bb conv.fresh frame off
26 T sedan street rod