Bondo question

Argeo · 10-22-2004, 09:18 AM

Hi,

My car is stripped to the metal (77 911) and I am getting ready to pull some of the dings and then bondo. My question is, what do I need to clean the metal with before I bondo. After the bondo I will be using that self etching primer before the primer that the paint goes on. I was thinking I had to buy some of that Dupont stuff that turns the metal a shade of blue but am not sure I need to now. Guy at supply store said I should just be able to clean with reducer.

The Bondo I am using is:

FIB 632 (first layer)
FIB 157 (middle layer)
FIB 420 (finish layer)

Any suggestions?
Thanks,
David

Rot 911 · 10-22-2004, 09:20 AM

I just clean the bare metal with Prepsol or lacquer thinner. Bondo is made to adhere to bare metal. Anything more than a 1/8" layer is too thick.

Argeo · 10-22-2004, 09:32 AM

Thanks Kurt. The guy who did the bondo before me just caked it on and didn't really take any time to pull the metal correctly. I am no expert, really a novice but should be able to cut the bondo down considerably. I will give the previous guy credit though. I didn't even know the bondo was there until I stripped and the paint job must be about ten years old.

Fortunately it there is no rust or rot to deal with on the rear quarters.

Maybe you can help with this one. The car obviously had a rear accident. New bumper in the rear plus the sections right around the rear tail lights were cut out and replaced. I would say from the middle of the bumper extension piece to the rear tail light. All cut out and replaced. Anyways, not sure how he did it but it is some type of weld but it is like someone poured on a solder and left leaving it sort of bumpy. Can I just sand with an 80 grit and smooth out somewhat? This was all covered in bondo before. I am sure I will need more bondo but I am thinking I should perhaps get the area as smooth as possible first.

Thanks,

David

Rot 911 · 10-22-2004, 09:34 AM

David, can you get us a picture of the welds? You might be able to take an angle grinder and smooth the welds down a bit more.

RickM · RickM's Garage

I would use a grinder as well. Be careful though. If you heat the area too much with the grinding wheel you can warp the panel. Also, the sparks will damage paint, glass, rubber, vinyl, etc.

911pcars · 10-22-2004, 10:42 AM

If it's solder, I suggest using a body file. You'll have more control over how much to remove. If you're careful, you can file the solder down to the level of the surrounding metal and minimize the amount of filler to complete the job. The less filler the better.

Sherwood

ruf-porsche · ruf-porsche's Garage

Quote:

Originally posted by Argeo
Anyways, not sure how he did it but it is some type of weld but it is like someone poured on a solder and left leaving it sort of bumpy. Can I just sand with an 80 grit and smooth out somewhat? This was all covered in bondo before. I am sure I will need more bondo but I am thinking I should perhaps get the area as smooth as possible first.

Thanks,

David

Before there was BONDO there was LEAD.

Body file would be the best way to shave it down.

Argeo · 10-22-2004, 12:40 PM

What is a body file?

Sorry, no digital camera.

How does lead work. DO they just pour it between the pieces of metal being connected or is it a different type of weld?

Thanks again,

David

scottb · 10-22-2004, 01:24 PM

Quote:

What is a body file?

It's a flexible file that is designed to handle the contours of your car. Go to your local Autozone or Pep Boys, they usually carry all sorts of DIY body repair stuff.

RoninLB · 10-22-2004, 06:06 PM

I'm an unusual example due to the Atlantic Ocean so fwiw.

I'd pull at least one bondo area down to metal to check for rust spots. I use all metal body filler as the big base. I finish with plastic bondo only applied very thin. I never use that red soft putty, forget the name, for detail finishing. DX-40 is a great primer base.

911pcars · 10-23-2004, 01:05 AM

A body file is a mill file (curved teeth spaced about 1/8" apart). They are rigid flat files attached to a handle of some sort. Lead, being relatively soft, is easy to shape and contour with a body file.

Lead is melted onto a tinned bare metal surface with an acetylene torch (soft, low oxygen flame), then in a semi-molten state, spread into position with a wooden paddle and heat. The process is much like soldering wire. Tinning is a thin layer of lead applied to the bare base metal to accept a thicker layer of lead buildup. Like filler, lead should be applied thinly as it's heavy; most of the metal work should be close to final shape before applying it. I'm sure you can google some info about lead work.

BTW, lead is toxic and shouldn't be inhaled.

Sherwood

RickM · RickM's Garage

Quote:

Originally posted by RoninLB
I never use that red soft putty, forget the name, for detail finishing. DX-40 is a great primer base.

You may be thinking of Nitrostan which is used to fill very small scratches in bondo. I've never had good luck with the stuff as it always seemed to be incompatible with other materials.

RoninLB · 10-23-2004, 10:46 AM

Quote:

Originally posted by RickM

You may be thinking of Nitrostan .

yep

audi2.7t · 10-23-2004, 12:28 PM

Also ,a word of caution on self-etch primer.......it doesn't play well with bondo or any plastic or epoxy based material and will usually bleed through when used on them.

Willem Fick · 10-25-2004, 01:18 AM

Argeo,

Make sure to use a coarse grade of sandpaper (80 grit) on the metal areas where you want to apply bondo. Clean the metal thoroughly afterwards with thinners or benzine. Apply the bondo in a few thin layers, allowing to cure between applications. Using a foam block, sand it down with 80 grit to approximately the right profile, and then use progressively finer grit paper to finish it off nicely. Stop at 220 grit. Now apply some etch primer over the entire area, and sand it again *lightly* using 220 grit yet again (audi2.7t is right, it does bleed through, and will not stick to plastic...). Now thinly apply some fill-primer to hide the scratches left by the 220 grit, and prevent bleeding, and sand the whole lot down with 400-600 grit paper (try not to use water, as fill primer is porous. Apply another thin coat of etch primer, and then follow with whatever final coating you choose.

Remember - the secret is *thin* layers, and keep in mind that the better your finish is before applying you final coat of paint, the better the end result will be.

Willem Fick

Argeo · 10-25-2004, 07:10 AM

Thanks guys for all the info. I will print and proceed. I bought my bondo's on Saturday. There were three in total. One that I guess has fiberglass in it for the first layer, then a second layer that is more workable and then a finishing putty.

So just to make sure I have this right, put bondo on clean metal that has been sanded with 80 grit. After I get the first 2 bondos to the the profile I want, spray with entire area with etching primer and then sand off with 400-600 grit sandpaper. The apply putty.

While i am here. I know flux core (non gas) is messy than mig (with gas) weld. Is it weaker also? The reason I ask is that being on a very tight budget, I have decided to use flux where the weld will not be seen and the gas on the areas that will be seen. One example is I cut out a piece of metal that the rear tail light rests on, I then added a new piece using flux core. It won't be seen but is it weaker? Is so I will gas up and replace. Let me know.

Oh, thank goodness for grandfathers that always fixed everthing themselves. I was visiting mine yesterday and come to find out he has a sheet metal nibbler and a grinder for cleaning up my welds.

Thanks guys,

David