i've noticed whenever pros are prepping a vehicle for painting and they find bondo under the old paint from previous repairs they usually remove it and redo the damaged area with more filler.what would it hurt to just leave that area alone and prime and paint over it?i've found some bondo areas on my repaint project.do i need to remove it or can i just rough it up and apply a coat of fiberglass filler over it? thanks.

Could you leave it? Provided it isn't cracked and falling off sure. However I wouldn't. I have a 67 Ford PU I'm "cleaning" up. Found several places where nearly 1/2" of bondo was used. Some spots has bondo filling rust holes. I can't trust another person's body work. Besides I don't think it adds much more work to the job if you're considering using the fiberglass filler on it anyways. Might as well get down to bare metal.

Just in case there is rust under there.

I would say if you KNOW the work is good work and is not there just to cover up something that could have been fixed better, Yea, you could leave it. If its done right, why take it all off? I would bet shops do this solely for the reason of not having to redo THEIR work for someone else's possible bad job. Its not worth the risk. If there is more than 1/4 inch of filler, strip it off. Im not a pro by any means, but 1/2 of filler is WAY to much. From what I understand, 1/4 is pretty much the limit, and 1/8th is better.

thanks guys,the bondo is thin and in good shape.will fiberglass filler stick to it? the chevelle will be garaged and will never be exposed to rain.it will only be driven occasionally on the street and at the drag strip.

why do you want to put fiberglass on it ?

why do you want to put fiberglass on it ?

its what i have on hand.its high quality short-strand fiberglass filler.its waterproof.it works on metal.i've been real happy with it so far.will it stick to bondo?

I'm sure it would. Provided you roughed the surface to give it some bite. But why? If the filler is already level anything you add on top would have to be sanded right back off. If you prefer the quality of the fiberglass filler just remove the thin layer of old bondo and start from bare metal.

To me, the fiberglass filler is to fill deep voids you don't want to metal work properly or to patch up holes. Use a little over seams where you're not sure if regular filler would stress crack. It's way too hard to use as filler that you're trying to sand flat to get a finished surface.

Peter

thanks guys,i guess i'm into pain but i really do like the durability and waterproof properties of the fiberglass filler.yes,its a lot harder to sand than bondo but i guess i'm just getting accustomed to working with it after using it to blend my harwood scoop into the factory hood.i plan on shooting hi-build primer and sealer over it anyway so i can work out any uneven surfaces by blocking and guidecoating.

I'd remove it to see what's under there. It could be a rusted out area, or it could be a dent that's three or four inches deep, which is not what filler is intended for. Also, if it's older body work like what I found on my car, I'd remove the old stuff and use some of the more modern fillers which are way better than the fillers used twenty years ago.

I agree with removing all the old work that's been done just to be on the safe side. I wouldn't want to get done putting hours and hours of work and $$$ for materials to see a bubble appear from an old repair I thought was OK. If you're ripping her down, take her all the way. Some of the older fillers I've removed over the years were major junk compared to the products we have today, some were really soft and porus. Did you mold your scoop to a steel or fiberglass hood? Use Fusor adhesive, then blend with fiberglass? Bob

Bob,i used 3M Readymix panel bonding adhesive.i had to buy a special applicator gun to apply it.(kinda pricey).the Harwood 4" cowl scoop(with flange) was designed to mount through the underside of the hood.i used up 2 packs of 3" cut-off discs cutting out the webbing and making the giant hole in my factory hood.i have since bought an air nibbler.(works much better.)once i stuck the sanded fiberglass scoop on i used sheemetal screws to hold it together until the adhesive dried.next,i removed the screws and sanded all the surfaces which would get the short-strand fiberglass filler.as of now its looking pretty darn good.i hope to start posting some pics of my chevelle project soon.the amount of man hours invested is going to be unreal.now i know why the aftermarket hoods cost so much!

Personally, i would take the bondo off and try to rework the metal so you will be able to use less bondo to fill in the area. If there is rust holes filled with bondo i would make a patch for the hole since you will see the bondo through your paint in the future.

thanks a heap! graemlins/thumbsup.gif

The adhesives we have today make successfully bonding these fiberglass scoops on a possibility. Years ago when only fiberglass was used you had like a 50/50 chance if was going to work. I've done a couple now with the Fusor adhesive and blended them with mat and resin followed by everglass and regular filler and they sure are holding up well, even with the extreme temperature changes up here. Glad you hear you used an adhesive designed for this, Bob

i took everyones advice and dug the old bondo out.and yup!you guessed it,a little rust here and a little rust there under the old bondo.overall,its not too bad,i'm gonna get "into the zone" again tomorrow and make some more progress rubbing out the rust in preparation for the filler.i guess i'll load my heavy metal c.d.'s and pretend i'm a young whipper-snapper again!thanks fellas! tongue.gif

bowtie - if ya got any holes weld them first

will do! thanks! graemlins/thumbsup.gif

after removing all the rust from the pitted areas and surfaces around the rear window,i'm left with a lot of bare metal area that has to be smoothed before priming.should i cover all this bare metal area with polyester putty and smooth it down,or should i use fiberglass filler? the putty seems to be the better choice as it spreads smoothly and evenly and seems to stick to semi-smooth metal better.should i apply etching primer first before the putty? thanks.

yep, see! You did the right thing. That rust might have stayed dormant, or might have eaten back out through all your hard work in 2-3 years. Now you will KNOW it was cleaned, welded up, and done right. Peace of mind is worth the time invested.

things are looking good! borrowed a buds small sandblaster to remove the rust and crap from the little trough around the rear glass.theres no substitute for the sandblaster when you need it. :rolleyes:

oh yeah,the bare metal is now primed before the sculpting begins! :D