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Thu Feb 19, 2009 3:08 pm

I have an '88 Vanagon Wolfsburg that has a crack in the rear bumper from the previous owner and I'm finally getting around to thinking about fixing it. Does anyone have any recommendations on a good patch material that I could use to do this right?

Thu Feb 19, 2009 3:52 pm

Here's a couple pictures of a bumper repair. If the bumper is cracked all the way through, you need to reinforce it somehow. This bumper had some metal plates rivited to the back side for strength, then a fiberglass bondo was used on the front. The resulting repair was undetectable from the outside. I never even knew the bumper was repaired until I took it off once. You could probably also glass both sides for strength if you can do fiberglass work, but the special bondo is a good solution.

Thu Feb 19, 2009 4:04 pm

Many folks will use fiberglass (polyester) to repair the bumpers. THis is wrong, they are not made with polyester resin, but with epoxy resin. The fiberglass eventually stats to come off, as it really will not stick to the base material.

So the better way is this:
Get a Dremel with the fiber re-enforced cutting wheel and make a 'V' along the crack. Then make a 1/4-1/2" depression along the crack. THis allows you to put some material in the crack and then put a layer of glass straddling the crack. Get some of the glass and cut it up to a chopped up state. Then get some JB weld, mix up a good batch and paint up the crack and mix the rest with the chop. Stuff the chop mix into the crack and smooth it down. Let this sit overnight. Smooth out the high points after it is set up with some sandpaper and the mix up some more JB Weld, paint the entire depression you made with the JB weld (lightly). Then place a pice of glass clothe the length and width of your depression on some plastic from a ziplock bag and paint the JB Weld on the glass fiber, both sides. Peel the impregnated cloth to a new piece of plastic. use the plastic as a carrier to place the strip over your depression and smooth the cloth out through the plastic. Try to squeegee the excess epoxy to one side so you can clean it up. You want a resin poor layer. Do this twice, letting the epoxy set up each time and smoothing the high points out between layers.

When you have done this, you can sand it smooth with a block and wet & dry (do it wet). Paint with some high build primer, sand again with fine and do a final coat. No crack now and it will be strong.

Thu Feb 19, 2009 4:07 pm

I may have mispoke on the bondo then, it was probably reqular bondo if it isn't a fiberglass material. Who knew? I just found out my oil filler extends. :wink:

Thu Feb 19, 2009 4:38 pm

I had to take a nauseating number of composite repair classes. Don't feel bad, I actually stumbled here into Samba a few years ago seeking the secret of fire, still looking and eating cold food.

The fiberglas mistake is a very common one. It is easy to tell,when you wiz a bit of the material of with the Dremel, the fiberglass will have that heavy polyester smell, epoxy will be sweeter, less organic chem lab in smell.

Thu Feb 19, 2009 6:07 pm

3M makes several products which can be used to repair various "plastic" bumpers. I don't have any personal experience with them, but I did watch most of the videos on their site. Even if you don't use their products, the videos may provide you with some good ideas/methods for doing your repair.

http://solutions.3m.com/wps/portal/3M/en_US/3MAutomotive/Aftermarket/Training-Resources/Videos/

Best of luck.

-Nick

Thu Feb 19, 2009 6:20 pm

Hey DP, do you have a source of epoxy resin? Ive gotta fix my bumpahs, and im also making a cowl for a model airplane im finishing up. I found out the hard way about polyester resin, it likes to eat white foam. :oops:

Thu Feb 19, 2009 6:29 pm

ProvoCyclist wrote: Hey DP, do you have a source of epoxy resin? Ive gotta fix my bumpahs, and im also making a cowl for a model airplane im finishing up. I found out the hard way about polyester resin, it likes to eat white foam. :oops:

try West Marine

Thu Feb 19, 2009 6:31 pm

ProvoCyclist wrote: Hey DP, do you have a source of epoxy resin? Ive gotta fix my bumpahs, and im also making a cowl for a model airplane im finishing up. I found out the hard way about polyester resin, it likes to eat white foam. :oops:

These guys make great products.

http://www.westsystem.com/ss/

Thu Feb 19, 2009 6:39 pm

There are loads of great laminating epoxies, but after you pay for shipping they get expensive. You can buy the 'Industrial tube size' JB Weld. It is a fine epoxy with a long working time and excellent strength. The big tube set is $18 at Ace, it will last a lifetime.

JB may be a bit heavy for a model, but if you use the Saran Wrap/or other plastic film technique to squeegee out the excess resin it would be ok.

Use Isopropyl Alcohol to clean up. Use ethyl alcohol to drink to relax afterwards.

Sun Feb 22, 2009 2:39 am

Thanks to everyone who posted replies. Dog Pilot - I think I will try your tips with the JB Weld, etc.. I will also be following your advice on the ethanol, although I'm well familiar with that technique.