Any bondo tips?

[LobsterThief]

I've been restoring a 91 MJ and have primed the majority of the truck (pics to follow soon in my build thread).

 

Anyways, there are a few spots that have a small amount of rust. There are also some spots that are dinged. All sports are less than the size of a dollar bill.

 

I'd planned on grinding some of the rust out, sanding, and bondoing it, etc. However, I've never used bondo before. Aside from the obvious task of reading the package, does anybody have any bondo tips?

 

Thanks!! She's almost ready for the road

[drcomanche]

It is a surprisingly easy to do project, but it will require some time. Let me see if I can remember some of the tips for it.

 

Don't make too much. It dries fairly quickly and the drier it is, the more difficult it is to work with.

 

If the dent or spot is too deep, don't worry about trying to get it level in one go. You can do multiple layers of bondo to fill a dent.

 

If you don't already have them, some soft plastic scrapers(should be sold with the bondo) and a rasp and sanding block are pretty useful.

 

Do one layer bondo, then sand it down smooth to where you can't see sanding lines or streaks. Then do another layer of bondo and repeat until it is where you want it and smooth.

 

And probably most important, take your time. It will turn out better in the end if you aren't rushing yourself.

 

I think that's about it, so good luck with it.

[LobsterThief]

It is a surprisingly easy to do project, but it will require some time. Let me see if I can remember some of the tips for it.

 

Don't make too much. It dries fairly quickly and the drier it is, the more difficult it is to work with.

 

If the dent or spot is too deep, don't worry about trying to get it level in one go. You can do multiple layers of bondo to fill a dent.

 

If you don't already have them, some soft plastic scrapers(should be sold with the bondo) and a rasp and sanding block are pretty useful.

 

Do one layer bondo, then sand it down smooth to where you can't see sanding lines or streaks. Then do another layer of bondo and repeat until it is where you want it and smooth.

 

And probably most important, take your time. It will turn out better in the end if you aren't rushing yourself.

 

I think that's about it, so good luck with it.

 

Awesome tips, thanks!! :)

[raviolli]

also, once you think youre pretty close in shape, you can use a guide coat...or just a quick mist of spray paint dark enough to see and go over it really quick in a higher grit to see if you missed any spots. if theres a high spot, youll see the bondo show up much quicker. if after sanding you see a spot of paint that hasnt even been touched, that tells you theres still a low spot.

[Akula69]

Some that I have found to be useful:

 

1) Be sure to grind the old finish down completely to bare metal in and around the repair. If possible grind and repair on the same day to avoid 'flash rusting' which can cause the bondo to release from the metal later.

 

2) Never apply in a patch more then 1/8" thick if you can help it. Thicker bondo can sometimes expand at a different rate when the vehicle is left out in the sun, causing the patch to 'pop' off. If the spot being repaired is too deep, there are two directions you can go in: If you have lots of access behind the dent, you can try tapping it out with a hammer and dolly; or, you can drill some small holes in the panel at the damaged spot and use a dent puller (commonly available at auto parts stores) to pull the depression outwards. If you have access to the rear of the panel you can apply a rust inhibitor (undercoat or primer) to the raw edges of the drilled holes.

 

3) A thinner putty called Glazing Putty can be useful in the final stages of the dent repair. It fills and covers micro air pockets and scratches in the sanded surface and is also commonly available at auto parts stores.

 

4) Generally, regular laquer-based primer is sufficient for temporary cover of a repaired patch, but before the finish coat is applied a special primer called 'epoxy-sealer' is a good idea to prevent a reaction between the feathered edge of the origional paint and the new finish. Also, the least expensive laquer based primers usually only prevent rust for approximately a year before problems occur.

 

5) Larger holes in a panel should have a backing of fiberglass applied to provide stiffness for the bondo. Any hole larger then the diameter of a coffee cup needs the backing because if pressed upon the bondo only repair will collapse inward.

 

Good Luck!

[SubSonic]

And always make sure you've completely sanded out all the marring from the low grit paper with the high grit stuff. It's amazing how often people don't completely sand out and leave marks, if only slight from sanding.

[LobsterThief]

Some that I have found to be useful:

 

1) Be sure to grind the old finish down completely to bare metal in and around the repair. If possible grind and repair on the same day to avoid 'flash rusting' which can cause the bondo to release from the metal later.

 

2) Never apply in a patch more then 1/8" thick if you can help it. Thicker bondo can sometimes expand at a different rate when the vehicle is left out in the sun, causing the patch to 'pop' off. If the spot being repaired is too deep, there are two directions you can go in: If you have lots of access behind the dent, you can try tapping it out with a hammer and dolly; or, you can drill some small holes in the panel at the damaged spot and use a dent puller (commonly available at auto parts stores) to pull the depression outwards. If you have access to the rear of the panel you can apply a rust inhibitor (undercoat or primer) to the raw edges of the drilled holes.

 

3) A thinner putty called Glazing Putty can be useful in the final stages of the dent repair. It fills and covers micro air pockets and scratches in the sanded surface and is also commonly available at auto parts stores.

 

4) Generally, regular laquer-based primer is sufficient for temporary cover of a repaired patch, but before the finish coat is applied a special primer called 'epoxy-sealer' is a good idea to prevent a reaction between the feathered edge of the origional paint and the new finish. Also, the least expensive laquer based primers usually only prevent rust for approximately a year before problems occur.

 

5) Larger holes in a panel should have a backing of fiberglass applied to provide stiffness for the bondo. Any hole larger then the diameter of a coffee cup needs the backing because if pressed upon the bondo only repair will collapse inward.

 

Good Luck!

 

Wow, good info. I'll only use it for the smaller stuff. Thanks!!