fiberglass vs. bondo - Vintage Mustang Forums

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post #1 of 8 (permalink) Old 04-10-2003, 06:40 PM Thread Starter
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I know this has probably been addressed many times before but I'm gonna ask anyway. I have done some bodywork before(notice SOME) and am gettin ready to do some more on my 68 F100. I just need some suggestions. I got a small (apporx. 2" diameter) rust hole on both doors and don't want to patch the holes with sheetmetal. I've done some bondo work before but never any fiberglass work. This is not a show truck by any means but I want it to be presentalble, the rest of the body is perfect. Any suggestions on which will be easier, more durable, etc. Thanks.

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post #2 of 8 (permalink) Old 04-10-2003, 06:56 PM
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I have used fiberglass with good results. It never showed any signs of lifting or anything else. I had sheetmetal welded in, though.

Bondo is said to be easier to work with, but it absorbs water. Every bondo job I have seen has been thick and showed signs of bubbling. It just doesn't seem to hold up as well. You aren't supposed to put it on very thick, though. I think the max recommendation is 1/8".

Either way, I don't think either should be used to patch a hole. Welding sheetmetal in and then filling in low spots with bondo or fiberglass is going to be the most durable.

Mike Manley

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post #3 of 8 (permalink) Old 04-10-2003, 06:57 PM
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Be sure and get rid of all the rust first. the 'glass kits at wally world work great. I have used one kit to do quite a bit of work. Then use the bondo over the glass and smooth it out. Hey, do ya'll have any good shows in the Troy area? I live up by Lake Martin and would like to travel that way sometime to check it out...
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post #4 of 8 (permalink) Old 04-10-2003, 06:59 PM
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Think of it like drywall... you don't fill in big holes with drywall mud, you put the piece of drywall in the whole and then fill around it, and any lowspots/edges to make it look right...

I primarily use fiberglass to cover up weld areas... the fiberglass putty will resist water and keep everything sealed up so you dont' get rust in those joints...

then I sand that down, and apply the bondo over that, real thin, just to fill in the holes and give it a smooth look.


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post #5 of 8 (permalink) Old 04-10-2003, 07:00 PM
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Bondo is NOT waterproof,in fact it will actually absorb water if if left exposed to it (such as the inside of your door). If you want something thats easy to use and is waterproof, try using some Upol fibre all or bondo kitty hair.

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post #6 of 8 (permalink) Old 04-10-2003, 07:41 PM
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yuck yuck yuck...

neither of these are good. fiberglass filler is for people who are gonna get rid of the vehicle soon, and are dishonest. bondo is for the DIY'er in the suburbs, who doesn't want to spend money, it shouldn't even be sold on teh shelves at stores.

if you are gonna just put mud in the hole, then do it this way... first, cut the rusty edges off until you have pure clean steel, then use 40 grit flexible grinding disk to strip down the clean metal 2 inches around the repair area, then go to a good paint store, and buy some "all metal" or evercoat "metal-2-metal" and fill in the hole wiht that stuff. it is comprised mostly of aluminum, and will hold up in thick patches. there are 3 colors of hardener...
white is waterproof. you can harden any good filler with any of the three colors.

oh, and top of the all metal or metal2metal with evercoat z-grip or somethign similar. don't go with anything you can buy at walmart, it isn't worth the headache.

oh, and top the z-grip off with polyester skim coat, like usc icing, or evercoat thin ice.

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post #7 of 8 (permalink) Old 04-10-2003, 11:00 PM
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why not fiberglass mat works great
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post #8 of 8 (permalink) Old 04-11-2003, 06:05 PM Thread Starter
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The stuff I have is Evercoat aircraft filler. A friend of mine works for an aircraft refurbisher and he got me some. Is this what I need to use? Is it better than fiberglass? By the way, thanks for all the help.

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