Auto Body metal working

My tutor liked fiberglass, has worked well for me, takes some learning though...

I've had the best luck with mat (see no use for cloth in body repair), resin and sometimes adding some gel for a thicker consistency. Try to have some fiberglass/resin behind, metal and fiberglass/resin on top. In other words sandwich the metal a bit in between. Some holes drilled through the metal, with some fiber & resin oozing through seems to work too. Make sure you lay enough fiberglass (thick enough) to be able to sand it off smooth/flush with the original surface. On a hot, dry day you can keep working & playing with the patch till it starts to set, can be helpful in vertical applications. Can get you in a lot of trouble too if it sets too fast and you aren't quite ready for it :) Rough up any low spots and fill with bondo/filler. Prime, paint.

Fiberglass has the advantage of not burning off the backside of the metal panel which may be hard to get at afterwards to rustproof.

If I was just doing some touch up on a truck like you describe, I would see how well a rattle can Rustoleum type white paint matched. Learned a long time ago it isn't worth the hassle of trying for a super-duper paint job in ones driveway or dirty garage. I've had rust reappear overnight, didn't allow myself enough time to get a paint gun loaded up and shoot it after rust cleanup...

On Jun 3, 9:29=A0pm, "RogerN" wrote:

Before I had welding equipment, I did a bunch of that on the VW. Some held, some didn't. The stuff that held was done with fiberglass mat and repair gel from one of the local chain parts places. The approach was to cut the hole back to solid metal, ding the edges in slightly, remove rust and paint to bare metal, hit everything with a phosphate rust-converter wash, then clean everything off to squeakiness with acetone(was cheap when I did it). I cut a chunk of mat for the back side, one for the front side and then made up a holder from thin welding filler rod. This had an L hook bent into it, the purpose was to hold the back in place while plastering the front piece on. The idea was to sandwich the existing metal at the edges, approximate the contours of the surface and hold things together while the gel set, about 5-10 minutes in the summer. I had a poly board made for mixing bondo that I used for the gel and a bunch of scraper/spatula applicators of various sizes intended for bondo. They worked well for impregnating the mat and anything stuck on just popped off afterwards. After the stuff set up, I left it for a day and went at it with body files, sander and block. Looked OK after it was primed and painted, the places where I filled in the rocker panel holes don't even show 10 years later. Was not so lucky on inner fender holes, had to be redone about 5 years later. Probably too much flexing and impacts from road trash and rocks. Now I'd just weld patches on. So it CAN be done. If the damage is in an area where fuel lines run and you'd rather not drop the tank and flush things out, fiberglass repairs might be the answer. Need absolutely clean metal for it to stick. I really liked the gel for this, regular resin would just run away.

Stan

Or even braze (or solder) them

Much simpler to just use a fast-build primer - feather that, and paint the whole panel (door)

My fiberglass experience is limited to once making a fiberglass part for an R/C helicopter and making a couple of R/C boats by making a foam hull shape and glassing it. Also put glass cloth over a wooden model R/C hydroplane. I've always used epoxy with glass cloth, most of my glass cloth came from Wal-Mart, some from hobby suppliers. I also have a fiberglass kit for training to build homebuilt aircraft with the glass over foam method, but I never used the stuff yet.

So my fiberglass experience is limited but varied. I thought maybe cut out the rusted area, treat the metal remaining, and epoxy (or better) the glass part into place.

RogerN

What about for just a paint chip area (front of hood perhaps)? Would it be better to repaint the whole hood for a few chips or sand, paint, and compound?

RogerN

I've used a lot of fiberglass, with both epoxy and polyester (and some dabbling with vinylester), and what I tell people who want to try things like you're suggesting is to do it, and see what works for you. You can always cut it out and start over. There are standardized methods like the mat patches discussed by others in this thread, and they work as well as anything, but if you're talking about making a male and female mold, that ain't a standard method for vehicle body patches. You'll have to work it out on your own. As I said, I tried much the same thing, with mixed results, over 30 years ago.

I went through 50 gallons of polyester every two or three days when I worked at Ranger Yachts. I'd just as soon forget it, to tell you the truth. But working in shirts covered with globs of polyester and fiberglass needles every day, and leaving the seat of my car bloody as I drove home, from the rips in my butt that came from rubbing up against raw edges of hull layups before they were trimmed, did give me material for an essay that landed me a writing job at McGraw-Hill. d8-)

We could talk about this forever but you really have to just do it and see. The few basics we've discussed, such as the inter-bonding capabilities of steel, polyester, and epoxy, and treating the hardened resin for further bonds, may save you some heartbreak. But making shapes with the material itself really requires hands-on experience.

Regarding the cloth and mat: The binder in regular mat is made to dissolve in polyester resin (actually, I think it's the styrene that dissolves the binder). It will not dissolve in epoxy. If you use epoxy with common mat, you will have one hell of a mess and you probably won't be able to wet it thoroughly. I suppose you know that you can't use polyester with styrofoam. The foam will dissolve. It works fine with epoxy, but use polyurethane foam if you're going to use polyester resin.

Cloth is less of a problem, but the "chrome" finish on boat repair cloth, and most cloth you can buy through ordinary retail channels, is made to get a good bond with polyester. I'm told it doesn't bond properly with epoxy. My experience with it is inconclusive -- I can wet it out with epoxy, but I don't know how good the bonds are, compared to layups made with the proper cloth. Commercial users of epoxy/cloth layups use cloth made specifically for use with epoxy resin. If you want an expert answer, call the guys at WEST System. They're very helpful, in my experience. And they really know their stuff.

Treat it as a learning experience and you may well enjoy it. But expect things to go some way you didn't expect. It's very hard to anticipate how that material will behave until you've had some experience with the specific kind of application.

And remember, epoxy drools. It's anti-thixotropic, and thickening it up only makes the situation a little better. Adding fumed silica will make it slightly thixotropic and it does help. Polyester is much easier to work with. They use it as the basis of Bondo for some very good reasons, even though it's a lot weaker than epoxy, and it doesn't bond to steel nearly as well.

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If the body filler is level with the existing paint, then the new paint would be above that level, wouldn't you want your body filler to be 1 paint thickness below the surface of the old paint? For example, if you sand off

0.004" of paint, fill that with body filler, then shoot it with 0.004" of new paint, the final surface is 0.004 above the old surface. However it would seem that if you removed 0.004" paint, then repainted with 0.004" of paint, the surface should be even. Even if your paint shrunk 25% you would have paint 0.001" low instead of 0.003" high.

But like someone mentioned earlier, it's probably easier to spray an entire panel than it is to spray a spot and try to blend, not sure though.

RogerN

The traditional 1930s method was to soft-solder the patch to the panel, using excess solder, and then to file and then wet sand everything smooth and well-faired for painting.

Real automotive Body Solder is 70% lead 30% tin, but for something this simple ordinary plumbers solder (50-50) may do.

Anyway, one could tack weld the pre-cleaned patch into the pre-cleaned recess, and then do the soldering. This will be very strong, and will not have any mismatch of temperature coefficient of linear expansion.

Joe Gwinn

You are focused too much on the thickness thing. Paint layer is acually very thin. Depending on the quality of the factory application, you may find the sealer/base coat/ paint layer to be several thou thick. You can't make this up with just paint, and as I said, not good to load it up with primer. Unless your truck is gloss black, it *doesn't matter* if the new paint is a thou high, what matters more is the feathering/ transition area, and, of course, color match. Pointless to spot repair a lot of small areas to color-it's going to end up looking like Hell. DA the whole thing after you do the metal work , and let Maaco shoot it. revisit

JR Dweller in the cellar

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Ok, I can see how it would be difficult to rebuild the surface precision enough, though someday I may try just for the learning. I was thinking of sanding down original primer, paint and clear and trying to replace with near equal thickness of primer, base, and clear (My 1992 truck doesn't use clear though, saves a step).

I guess an interesting thing would be to see if any of the local colleges would like to repair my truck body for a reasonable price, I've heard of some doing this for about the price of materials. But my goal is not so much to have a perfect truck body as it is to learn some bodywork and painting skills I can apply on other vehicles. Kind of like when you make a hammer in High School metal shop class, the hammer is of little value but what you learn by making it can be valuable.

Anyway, after I get my experimenting and practicing done to my satisfaction, I may take it and have the whole thing sprayed. I figure my home compressor will be sufficient for touch up and detail but I don't think I could paint a car with that small of a compressor (though I could hook up 2 of my compressors and probably have enough air).

RogerN

If you want the repair to "disappear" do the whole hood. Most paints today are spec'ed as whole panel, and don't blend well. Sand the whole hood through the clear-cote to colour, clean out the chips, acid treat them, fill them, feather them, and repaint the whole hood.

Today's fast-fill polyester based primers (which is what I recommended) do NOT shrink. The thicker version - polyester spot putty

- works well for simple stone chips after removing and neutralizing all rust in the pit. The UV cure stuff works as well as the 2 part catalyzed stuff if you have a UV lamp to cure it - or park it in bright sun 'till cured. It is basically thin body filler (often referred to as "spray-on bondo")

A pro body man will do the whole panel.. A lot of "so-called" body men will try to "blend" the paint - and the clear-coat will peel off in less than 2 years.

I won't let even an insurance job "blend in" a panel on any of my vehicles any more.

Kid brother used to be one of the best auto-body men (and painters) around until he got sensitized to isocyanates. Really nasty stuff.

Hello Ed,

My understanding is that fiberglass *mat* is made specifically to work with polyester resin, as you've said. But fiberglass *cloth* seems to work well with either epoxy or polyester. I have not yet seen a vendor who sells different kinds of cloth for epoxy and for polyester---though I'm certainly willing to be proved wrong... :-)

I've been told that there are certain surface active agents (soaps, if you will) that may be added to epoxy resin; they displace water and enhance bonding of the epoxy to the glass. Most users I know do not use these agents, though.

The rocketry bunch at

and does a lot of work with fiberglass---literally thousands of large rockets have been built this way--- and it's almost exclusively with epoxy as the binder. A lot of these guys do some work indoors and I'm pretty sure that most would be divorced or kilt or worse if they used polyester resin. :-)

-- Best -- Terry

Roger,

I painted the right front fender of my Corolla with an ersatz HVLP paint gun and my home compressor. The compressor is 110 v 14 amp (I think) so it's definitely not a monster. It's a rollabout job with two tires. The paint gun was an el-cheapo HF HVLP gun, about $15. I had to thin the paint rather a lot but it still worked well.

The compressor was originally purchased to "paint" the tile and bathtub in the girls' bathroom, using a similar but larger gun. (For various reasons we couldn't easily replace the tub during renovation, and 1960's Vomitous Beige-Pink was considered an unsatisfactory color by the wife). Worked beautifully, and no one who has seen the job has ever guessed that it was a re-coat except the guy who noticed the one spot where it ran a bit.

-- Best -- Terry

Not a recommendation, but a question. Has anyone tried the water based automotive paints from Du Pont? I have not been able to find any cost data on them, or comments by users.

Dan

It may be, Terry. When I was working with lots of the material, some source I read said that large-scale users of epoxy for layups used a grade of glass cloth that didn't have the "chrome" finish used on cloth made for polyester, because the chrome finish wasn't compatible with epoxy. As I said, I don't know, because I've not used that much of it and never ran any tests.

However, at the time, S-glass was available with and without the finish. I bought some for a project, without the finish, for use with epoxy. Again, I never ran any comparative tests to see how it worked out. My tests are kind of crude, anyway.

It's become very sophisticated in recent years. I'd have to spend some time catching up to see what's available today. BTW, I was using pre-preg at the end of that time, which I grew to really like. If you refrigerate it just right, you can handle it like a sheet of rubber. It's really good for some home projects but you need to know someone in the business, because you have to buy pretty large quantities of it at a time. I was getting mine from Zeston Corp. until they sold out to Johns-Manville. They'd let me cut off as much as I wanted. What a deal! Most of that stuff is A-B cure, but Zeston had some with an amine hardener, or some other RTC hardener, that let you cure it at room temperature.

Their rockets would droop, anyway. I'll bet they know the latest. I'll have to save those links. Thanks.

BTW, what's the latest word on vinylester? I haven't seen much about it recently. R.Q. Riley uses it for his carbon-fiber recumbent bicycle, because, he says, you can use it with carbon fiber without the need to vacuum-bag it. Do the rocket guys use vinylester for anything?