Best Way To Repair Crack In Bumper?

[supark]

I can get an M3 bumper for next to nothing - the catch is that there is a crack on the bottom a few inches long (not visible from front).

What's the best way to repair this kind of damage? I was thinking of using a good epoxy like JB weld to glue a patch on the inside.

Here's a pic of the damage (decided to get it being that I can get it for so cheap). I'm thinking the only way I'll be repair it is using a patch.

[attachmentid=15693]

Thanks

[97alpineM3]

Get some good body epoxy.... mix it up.. and slap it on there.. then take some sand paper... and smooth it out... and you'll be fine....

Good Luck,

Les

[bigred318]

man i thought you were going to say that you have a crack in your stock bumper in which case my answer was going to be to buy an e36 m3 bumper, well you beat me to it. yeah make sure you sand it down flat, and then touch up the paint

David

[El Presidente]

I'd not buy it. If its cracked, its fiberglass. Even the slightest future impact can crack it again.

[supark]

It's a stock bumper and is made of plastic - I can get it for $60, so I figure it's worth it. I can sell my stock bumper for at least that much...

[97alpineM3]

if you mold the epoxy and let it set the correct amount of time before you sand it down.. there is no problem with stength problems... thats my opinion... I've touched up fiberglass bodys many many times with my fathers old 2002ti track build.... it holds good...

Good Luck,

Les

[supark]

From what I've read in other posts - I'm going to need M3 brake ducts to do the swap - are there any other parts I'll need?

I'm wondering if I can just use a comparable looking grill material from Home Depot for the grill (bumper doesn't come with one) and just spray paint it black.

[El Presidente]

if you're sure its plastic. Ive never heard of it cracking though.

[bigred318]

that is what i was thinking.. its takes a hard hit to crack the stock bumpers...

DAvid

[supark]

I've edited a post with a pic of the damage - I'm thinking the only way I'm going to be able to repair it is with a patch and epoxy.

[bimmerfan620]

Originally posted by supark@Dec 1 2004, 12:26 AM
I've edited a post with a pic of the damage - I'm thinking the only way I'm going to be able to repair it is with a patch and epoxy.

[snapback]241056[/snapback]

NO!!!!!!

<span style='font-size:10pt;line-height:100%'>Don't Use Epoxy and a patch!!, 1, if it is the BMW OEM M3 bumper, it is going to be Urethane, which is a flexible ABS plastic, a bodyshop could easily use their plastic welder and completely melt in a weld and sand it down to be perfect. Holds 100% as strong as if there was no crack. Otherwise, if you want a cheaper fix, which sounds like what your after, GO to Autozone, or PePBOYS, get the Fiberglass patch kit, comes complete with your fiberglass matt, resin, and hardener. your going to patch this from the inside, not outside. sand down the area around the crack with 80 or 100 grit sandpaper to get an adhesive surface. Your going to cut a peice of the fiberglass matt so that it covers past the crack on all sides by at least an inch. set it aside, you will need 2 peices total that are almost exact since you will make 2 layers. next, get a container you can poor the resin in, and mix in the hardener until proper consistency on instructions. make sure you've got the bumper near, cause this stuff sets up quick. 1st thing you do is get a paint stick or something similar, put the resin on the bumer, in the crack, around it everywhere the patch is going to lay. Then your going to put the fiberglass matt in the resin you mixed to let it get saturated. then apply the patch over the crack in the resin. get all the air bubbles out, do the same with the next patch over top the 1st one, and give it 15 minutes, it's hard and you can sand, or do whatever you want. Add more layers behind if you really want to. but the fiberglass is going to be more than strong enough. and to patch the crack from the outside, you can get a product called mar-hyde which is your finishing filler. this is what you'll sand down to the surface to completely hide the crack all together. that is the way I would do it, and I believe it would be your easiest way that will last without giving you problems.

Aaron</span>

[supark]

The problem is that finding a shop that's outfitted with a plastic welder is actually more difficult than you would think...

Wouldn't fiberglass in some ways be worse than using a patch of plastic with epoxy - because it would flex at all?

I've used fiberglass before for motorcycle plastics - but that doesn't flex quite as much as the bumper does. JB weld can do amazing things...

[bimmerfan620]

honestly, if someone is trying to tell you, well fiberglass won't hold like a plastic epoxy, they are wrong, it will hold better. And don't make your decision up on if you hit parking space spacers, or if you nail curbs, because your not supposed to be hitting anything with your car in the first place. Bottom line, I'm not going to say the epoxy won't hold it together, but according to proper bodywork, i don't think you would ever find guys recommending to use a plastic epoxy or JB Weld. 9 out of 10 times you will get Fiberglass patch because it is so strong. And quite a few large bodyshops have the plastic welders, just make some calls if you really are interested in that. It's my bit of information for you, take it as I deliver it, and make your decision, but do it wisely. because you dont' want to have to repatch it again because it didn't hold.

Aaron

[supark]

A friend suggested using a solder gun and some scrap abs plastic as fusing material - worked great and was free! I didn't think it'd work - but it seems to hold great.