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93EXCivic
93EXCivic UltimaDork
5/9/12 8:09 p.m.

Ok so I have a couple places on the Yugo that need repair (aka rusted thru) and they aren't structural and they will be very difficult to repair by welding cause they are on the lip of the hatch and they seem to big to use body filler. I have worked with fiberglass before but never to repair a car. So I was wondering what kind of resin and fiberglass I would use and also do I need a bonding agent to bond it to the body work?

Dr. Hess
Dr. Hess UltimaDork
5/9/12 8:31 p.m.

We are talking a Yugo, right? I mean, I just wanted to be sure...

Standard polyester resin and some mat or cloth, available anywhere from O'Reilley's to Lowe's. Clean up the rust area, beat it in a little bit, put the glass on, smooth it out, sand, bondo, Rustoleum, looks like new.

jere
jere New Reader
5/9/12 9:51 p.m.

Another tip (if you are dedicated to this method) is back the hole (outer side of the car) with something like duct tape. Then lay the FG against the hole (the inside of the car) and the duct tape. If the tape lays across smooth, the FG will be just as smooth after it dries and the tape comes off. Just make sure to clean the contacts good for the FG and get enough layers in.

jere
jere New Reader
5/9/12 9:53 p.m.

Oh and the resin is all you need for the bonding agent.

foxtrapper
foxtrapper UberDork
5/10/12 4:54 a.m.

Agreed, cheap polyester resin (the blue goey stinky stuff).

Epoxy resin is wonderful, but overkill for a Yugo.

Neither need anything but clean rough metal to bond to.

93EXCivic
93EXCivic UltimaDork
5/10/12 7:05 a.m.
foxtrapper wrote: Neither need anything but clean rough metal to bond to.

So do I need to remove the POR-15 in that area?

foxtrapper
foxtrapper UberDork
5/10/12 7:10 a.m.

Don't know. I'd be inclined to give it a try over the POR-15 on one spot and see if it holds well. If not, grind/brush it off and redo.

alfadriver
alfadriver UberDork
5/10/12 7:34 a.m.
foxtrapper wrote: Don't know. I'd be inclined to give it a try over the POR-15 on one spot and see if it holds well. If not, grind/brush it off and redo.

On the flip side of that, while you can fiberglass over evidence of rust, it seems like a bad idea- in that the untreated rust will come back- thoughts?

(hope POR works, since it theoretically will treat the rust that's not cut or grinded out)

MG Bryan
MG Bryan SuperDork
5/10/12 7:41 a.m.
alfadriver wrote:
foxtrapper wrote: Don't know. I'd be inclined to give it a try over the POR-15 on one spot and see if it holds well. If not, grind/brush it off and redo.

On the flip side of that, while you can fiberglass over evidence of rust, it seems like a bad idea- in that the untreated rust will come back- thoughts?

(hope POR works, since it theoretically will treat the rust that's not cut or grinded out)

I think the fiberglass is just a cosmetic fix, since he's only using it in non-critical places.

93EXCivic
93EXCivic UltimaDork
5/10/12 7:44 a.m.
MG Bryan wrote:
alfadriver wrote:
foxtrapper wrote: Don't know. I'd be inclined to give it a try over the POR-15 on one spot and see if it holds well. If not, grind/brush it off and redo.

On the flip side of that, while you can fiberglass over evidence of rust, it seems like a bad idea- in that the untreated rust will come back- thoughts?

(hope POR works, since it theoretically will treat the rust that's not cut or grinded out)

I think the fiberglass is just a cosmetic fix, since he's only using it in non-critical places.

Yeah a lot of places are going to be welded up (the floor boards and rear shock mounts are the two big places). But at the place where I want to do fiberglass it is going very difficult to weld up.

Curmudgeon
Curmudgeon MegaDork
5/10/12 7:59 a.m.

I don't think fiberglass would stick well to POR15. It has too shiny a surface and the resin needs a rough finish to stick to. Remember, fiberglass molds are basically shiny waxed surfaces that keep the resin from sticking to them.

Otherwise, I have used aluminum window screen as a backer and it works good. Use small screws or pop rivets to hold it in place, allow ~1/8" for the cloth/resin and go to town. Also FWIW, I found that the cloth is easier to sand to a smooth finish than the mat.

foxtrapper
foxtrapper UberDork
5/10/12 8:08 a.m.

Just glopping resin over rust isn't a good idea. It won't hold well, and the rust will very likely continue to grow. Especially with the polyester resin, as water works its way under it and through it quite well.

Brush it to as clean a metal as possible, and then glop on the resin.

alfadriver
alfadriver UberDork
5/10/12 8:12 a.m.
MG Bryan wrote:
alfadriver wrote:
foxtrapper wrote: Don't know. I'd be inclined to give it a try over the POR-15 on one spot and see if it holds well. If not, grind/brush it off and redo.

On the flip side of that, while you can fiberglass over evidence of rust, it seems like a bad idea- in that the untreated rust will come back- thoughts?

(hope POR works, since it theoretically will treat the rust that's not cut or grinded out)

I think the fiberglass is just a cosmetic fix, since he's only using it in non-critical places.

That's kind of my question- how good of a cosmetic fix if the rust shows bubles not too long after the repair. I figured that the rust would just continue, but have never worked with it, and don't know anyone who has.

If POR would seal it prior to the repair- win-win. Assuming that the POR and resin stick to each other....

93EXCivic
93EXCivic UltimaDork
5/10/12 8:17 a.m.

So assuming that the resin doesn't stick is there some kinda bonding agent that could be used to make it stick?

MG Bryan
MG Bryan SuperDork
5/10/12 8:21 a.m.
alfadriver wrote:
MG Bryan wrote:
alfadriver wrote:
foxtrapper wrote: Don't know. I'd be inclined to give it a try over the POR-15 on one spot and see if it holds well. If not, grind/brush it off and redo.

On the flip side of that, while you can fiberglass over evidence of rust, it seems like a bad idea- in that the untreated rust will come back- thoughts?

(hope POR works, since it theoretically will treat the rust that's not cut or grinded out)

I think the fiberglass is just a cosmetic fix, since he's only using it in non-critical places.

That's kind of my question- how good of a cosmetic fix if the rust shows bubles not too long after the repair. I figured that the rust would just continue, but have never worked with it, and don't know anyone who has.

If POR would seal it prior to the repair- win-win. Assuming that the POR and resin stick to each other....

Ah, I see. I was kind of just assuming that a wire-wheel was going to be taken the the rust to clean everything up, and the fiberglass was just going to fill the resulting holes.

Curmudgeon
Curmudgeon MegaDork
5/10/12 8:23 a.m.

Rust being basically a chemical reaction between oxygen and steel, anything which seals off oxygen from clean metal will prevent rust. So if it's wire brushed back to clean steel then coated with resin that sticks properly it should not rust. Any existing rust that was covered would continue to grow and rust is like water turning to ice: it expands and that's what pops the paint off.

POR15 can definitely be topcoated with urethane etc paints. Their Web site says it's compatible with fiberglass. http://www.por15.com/faq.asp They say you can put it on fiberglass but do not mention putting fiberglass on top of it, though.

NINJA EDIT: A rereading shows they say POR15 can be used with fiberglass cloth, I guess that means use it instead of the resin. Just don't get it on yer hootus.

foxtrapper
foxtrapper UberDork
5/10/12 8:28 a.m.

I've no doubt you can slather resin onto POR-15 and have it cure. I'm just not so sure how well it will stick.

Remember, any bond the resin has is purely mechanical. There is no chemical interaction with the substrate. Smooth shiny surfaces don't provide the "tooth" for the resin to stick to that roughened surfaces do.

If you scuff up the POR-15, the resin will bind to the roughened surface better.

Active rust will push a fiberglass patch up and off the surface. It won't come through the fiberglass patch, it shoves if off.

alfadriver
alfadriver UberDork
5/10/12 8:29 a.m.
MG Bryan wrote: Ah, I see. I was kind of just assuming that a wire-wheel was going to be taken the the rust to clean everything up, and the fiberglass was just going to fill the resulting holes.

Actually, I'm not a big fan of just wire wheeling rust- the gold car you see to the left- i'm pretty sure that parts of it where surface rust was showing- was just wired clean before painting- and over time, the rust came back. I would be a lot more confident in sanding it smooth- but even then, I would want to find some kind of treatment before anything further- primer, paint, epoxy, glass- whatever.

I figured glass, especially the polyester resins, would not do much to stop or seal rust. So I appreciate the answers. Not that I have any plans, just interest.

MG Bryan
MG Bryan SuperDork
5/10/12 8:32 a.m.
alfadriver wrote:
MG Bryan wrote: Ah, I see. I was kind of just assuming that a wire-wheel was going to be taken the the rust to clean everything up, and the fiberglass was just going to fill the resulting holes.

Actually, I'm not a big fan of just wire wheeling rust- the gold car you see to the left- i'm pretty sure that parts of it where surface rust was showing- was just wired clean before painting- and over time, the rust came back. I would be a lot more confident in sanding it smooth- but even then, I would want to find some kind of treatment before anything further- primer, paint, epoxy, glass- whatever.

I figured glass, especially the polyester resins, would not do much to stop or seal rust. So I appreciate the answers. Not that I have any plans, just interest.

It's not my preferred approach either. We're talking about a Yugo though.

93EXCivic
93EXCivic UltimaDork
5/10/12 9:01 a.m.

I will take pictures tonight to demonstrate what I am dealing with.

4cylndrfury
4cylndrfury UltimaDork
5/10/12 9:12 a.m.
foxtrapper wrote: the rust will very likely continue to grow.

This^^

A by-product of the oxidation of iron is water...which further oxidizes iron...which makes more water...which ...well you get the idea - this can happen even under very well sealed conditions (paint, epoxy etc) because the oxygen in the water is what does the damage. Rust will grow more rust, thats just the way it is.

I believe products Like POR stop the chemical reaction, thats why it can go right over rust without having to remove it.

foxtrapper
foxtrapper UberDork
5/10/12 9:32 a.m.

If it was actually a self perpetuating cycle, we'd be exploiting it for energy. It isn't so we can't.

The rusting process does not sweat out water. When iron contacts water, it reacts with the oxygen and releases the hydrogen.

Rusting is an oxidation process, which is essentially very slow combustion. A faster variant is the compost heap.

Trans_Maro
Trans_Maro SuperDork
5/10/12 9:42 a.m.

Wurth makes a rust convertor product that we use at work.

It's the best thing I've ever seen, you brush it on and let it dry. No water rinse afterward is needed. It dries hard and black.

Just a wash with some body solvent any you're ready to cover it.

We use another product called "miracle paint" by Bill Hirsch after the rust convertor. It's like POR15 only it's really, really thin and flow into all the pits and crevices and seals the metal up tight.

It's the best way we've found to kill rust other than cutting it out completely.

Shawn

subrew
subrew Reader
5/10/12 11:05 a.m.

How's the Saab 9-3 project coming?

jere
jere New Reader
5/10/12 11:36 a.m.

With the wire wheels you might be better off with a stainless bristled wheel rather than mild steel. I think the mild steel wheel can contribute to the rust.

I have had mixed results with POR-15, the worst rust spots keep rusting (fender wells). Maybe it wasn't applied with a certain humidity or something that was my fault but I am not going to buy it again.

Something else that in theory should work for chemically stopping the rust is paint with zinc or magnesium in it. Like galvanized steel fence or water heaters it could stop the chemical reaction. Anyone know more about this sort of thing? If it is applicable to automotive use?

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