Cowls and Bondo - stupid questions

[bigredbird]

Okay, after three years on this board I have to ask two stupid questions about things I see mentioned over and over -- cowl rust-through and bondo. As best I can tell from discussions, both of these are dealbreakers and/or the kiss of death for an otherwise nice-looking B-body.

First question: the cowl on my 72 is basically fine at the firewall, with just a little 3/4" rust hole that I patched and filled when I got the car in '08. But down in the "leafcatcher" area under the vent screens, there are 5-6 rust-through spots of different sizes from 1/2" to 1". When I had the hood off I got down in there as best I could, vacuumed and wiped down what I could reach, and sprayed primer. I cut two plexiglas plates to cover the screens (saw this on a Chevelle at a show, thought it was a great idea), and the car never sees rain and gets washed once a year. So... how badly do the rust holes inside the cowl affect the structural integrity of the car itself up front? And is there any way in hell of working on the rusted area from under the car, to treat the bottom side of the damaged steel?

Second question: my bird is definitely a bondo buggy to some extent. Big sections of the rear quarters behind the wheels are plastic, same with the back lower fender portions and even one corner of the DS door. But 90% of it was done really, really well - whoever did most of the work rebuilt the body lines perfectly and sanded it all smooth as glass. There's just one spot on one fender that looks like another previous owner did it, not as carefully or smoothly. So why do I want to invest in quarter sections, fender patches, and bodyshop fees, rather than fix the one roughest section and keep the plastic repairs? Is bondo just an aesthetic or philosophical issue, or an actual structural-integrity one?

Okay, those are my stupid questions of the month/year; I hope some of the board experts will make me a little smarter about them. :read2:

 

[Montclaire]

Well, I really don't agree with the plexiglass covers, but there is nothing actually wrong with them. Unless the rust is really invasive, pinholes aren't going to cause the car to collapse on itself. You can remove the dash and get to the backside of the cowl and patch from that end, or you can use something like POR patch, which is a sort of plumbers caulk. I have also heard of guys slightly thinning and pouring POR into hard to reach and pinholed areas, and this has worked for them.

In terms of past body work, any vintage mope in the rust belt that wasn't kept in a bubble has had rust repair, and up until the past couple years there has not been a really great supply of aftermarket metal. If the repair was done correctly at the time with what was available, then it is what it is, and I think that most appreciate that.

 

[RustyRatRod]

Ther 65 Coronet I just bought has outer cowl rust. Kiss of death? My big old BUTT. I'm drillin out spot welds and that beeotch is comin OFF. Gonna get all the bad metal out and add new in. Also gonna fix whatever rust there is in the inner cowl, if there is any.

 

[Ron 73]

yep! I wouldn't get to thinking its a matter of time or something.. Anything can be repaired, if the body works done in the right way, it should hold up for a long time! Mine always did and ive patched a few with metal using Dur a glass then bondo for finish sanding, the duroglass is tuff stuff, biggest thing is getting rid of the rust, you have no idea some of the stuff ive found doing some cars, pop cans newspapers and tin foil stuffing holes and bondo put right over it and the rust and everything, and they wonder why the body work only lasts 6 months lol... I primered a blazer for a guy that insisted on tin, pop rivets and putty and ONLY primer, i told him if he wrecked it just call for a broom, lol, i got paid and it looked real good, the kids dad wanted me to do the same to his blazer but i refused. I told the kid that primer is not paint, don't drive it that winter without paint and he worked in Cleavland.. do i need tell you what it looked like the following spring! Serious as can be!

 

[RustyRatRod]

If you work with fiberglass or bondo, there are two BIG rules not to break. Get your work CLEAN as possible and DRY as possible. Fail to do that, and forget it lastin anytime at all.

 

[Photon440]

Years past, I had problems with fiberglass sticking to steel no matter how clean and dry. It looked good, but a strong pull would start to separate it. Then I switched from polyester resin to epoxy resin, and it was bulletproof.

That was before I had a welder, I don't do repairs with 'glass now.

 

[PurpleBeeper]

I also suggest using a phosphoric acid based rust-proofing coating (llike Rust Mort) on the repair spot before putting in bondo/fiberglass to prevent the rust from bubbling out from beneath.

 

[Meep-Meep]

Cowl rust is probably the one problem area that will affect you the most and that's because your interior fills up with water. I don't think a hole here and there is going to affect the structural integrity of the car, provided the rust hasn't eaten away at the spot weld joints along the whole piece. So if you just have that annoying hole that lets water in the car you can fix that a number of ways.

Using my old 71 Ranchero as an example here is what I did. In the pics you will see the vent hole (actually capped from the factory) that is supposed to have a nice round hole but the right half is eaten away by rust. I made a template out of thick paper then transferred that to a piece of sheet metal. I had several choices for attaching the sheet metal and ended up using what I felt would yield the best results. A couple of sheet metal screws and rivets to make a good mechanical joint then JB Weld to seal the seam and small gaps. Welding was out of the question because no way I could remove enough rust to get a good weld, so I wire brushed then treated the metal with rust converter and applied some good 'ol Rustoleum. Figuring I had a pretty good bond between metal and paint I proceeded with the epoxy and installing the patch. After that set up I used a variety of flexible sealers, sprays and mud on the water side of the joint to make double sure nothing got through. Put the factory cap back on with a new foam gasket covered with the right stuff sealer and I'm ready for Portland OR weather. By the way, I did this with the dash removed, which made it MUCH easier to get at.

 

[WmBaldwin57]

Ok, I've read a bunch of these threads concerning cowl repair and it appears to be a common problem and my 65 Coronet is no exception. But other than the one guy I haven't seen anything where someone tried to address the cause "Leafcatcher". My car is a junk yard dog composed of about 5 different cars and was stripped at one time to make a bracket racer. So 'restoration' is really not an option and I really prefer to customize it a bit. I know the purist are cringing about now, but drive your own car I'm thinking about putting either a Vintage Air or Classic Air system in this and my question is 'Do I even need these vents" I'm thinking of replacing the vents with a solid flat panel....NO more Leaves.

 

[YY1]

Wow, Meep, that rust in that exact spot is why I finally sold my 71 Torino GT.

The only other rust was a quarter sized hole in one quarter panel, but that cowl vent was as bad as yours.

I knew I could never do it right without spending as much as the car was worth, and it was a kind of nice car.

I've seen a LOT of mustangs with plexi-glass over the exterior cowl vents.

This is one area that gm got right- theirs are seperate covers and they bolt/screw on.