Fixing up under the body rust problems

Yes, old cars and rust, 1994 model.  I decided to work on my wagon and get it back on the road, inspected and all that.
After repairing the 2 leaky exhaust pipes, looking around, I found small rust thru in the floor panels, especially close to the frame where it curves up and meets another panel at the seam.
I scraped aways the dirty rust, what a mess. Best way for me to fix this is mix some sawdust into PL Premium polyurethane CA, and fill all the holes up, then I used a chip brush and painted pure PL all over the panels that were rusting that I have access too. The body area on top of the frame looks ok, I still see painted metal. Dont expect PL to stick to grease, oil or dirt, it will stick well to clean rust. Even if rust looks clean, it may be oily, especially under the car, so either hand sand it or use alcohol maybe to clean it. If you use a steel brush and lots of loose rust is coming off, that is good for a clean surface, Use a 2 inch chip paint brush and brush it hard into the rust, and paint on a waterproof  coating.

If it does not stick, you can easily peel off this PL coating which is like a rubber. Advantage of PL, it is rubbery, flexes, no cracking, 100% waterproof. But you should paint it as UV light will wreck it.

Looking above the rear axle, where a rubber body mount bolts to the frame, it is gone, collapsed. Cant tell anything is wrong from outside the car or driving it around.

I really blame the car makers for how they put this stuff together. They spot weld it which leaves gaps and they may or may not try to seal adjoining pieces of metal. Then the other thing, they leave large drain holes. That lets in dirt, dust, salt, water, and the metal disintegrates  from the inside to the outside.  They could do a much better job to preserve things, but they dont care, they make cars to last only a few years on purpose, it is deliberate. Better to have no drains holes or punchouts, and weld the entire edge perimeter of panels, then go ahead and seal the underbody, maybe hot dip galvanize whole frame and body first then a paint coating, then something called fluid film.

Car is still driveable and you would never know. the only really good fix would be to take the body off the frame to fix things.

Then there is the frame itself, same kind of issues. All the frame holes, over the years get filled with dirt, rust and crud. When it gets wet, takes forever to dry, so it is rusting all the time inside the frame. The way cars are made, the only way to preserve them is not drive them in everyday weather.

Of course about 5 years ago, I had to repair the spare tire well, which had completely vanished.

""I really blame the car makers for how they put this stuff together.""

For those of us who can remember when hidden gas fillers were the thing, this is exactly how the Japanese came to dominate once-mighty Detroit.

American cars in the North, Northeast, and Southern coastal areas could be expected to have fully perforated rust holes after about three Winters.

The Japanese cars were simply designed to reduce the moisture and salt trap areas. There was no additional costs in material or precise assembly methods, just a culture that vehicles were not supposed to be scrapped after a half-decade of service.

American body design is light-years ahead of what it used to be, but there is still much room for improvement.

sawdust??

Rev Bob wrote:

sawdust??

Since the PL is a moisture cured substance, If you want it to setup THICK, it needs that sawdust as it needs moisture for the cure, and it also bulks it up as an extender. Can be painted or stained, sands smoothly. Mix it with sawdust around 40% dust- 60% glue. Apply with a putty knife.

Give it a try, you'll be surprised how well it works. it also works great to fill wood gouges, holes , missing sections, if mixed with sawdust, the same with metal holes.
You can put masking tape over the glue and peel off the tape after it sets. You can use a plastic cereal bag to shape the glue, it wont stick to the HDPE. You can use FG drywall tape as a skeleton to hold the adhesive in place, or if the holes are small it works fine by itself. You can add as many coats as you want it sticks to itself.

I buy the 28 oz. large cartridges, lots cheaper by the oz. than the 10 oz. tubes
This stuff swells up as it cures.
I will link some pics tomorrow.

This is it here, this is a structural adhesive and a filler.
https://www.homedepot.com/p/Loctite-PL-Premium-28-fl-oz-Polyurethane-Construction-Adhesive-1390594/202020474

pictures before any spray paint

https://photos.app.goo.gl/SdsAr8cfoEh7za8K8
https://photos.app.goo.gl/ynczjNDUwBk7p9TR6
https://photos.app.goo.gl/CHKQ9qgYDKsNMaE78

I would definitely call that outside the box thinking!

Probably provides some sound deadening as well.

I suppose so, its like undercoating, but it dries to a rubbery substance. And it is paintable. And it is waterproof, not water resistant. I have used it on the bottom of my boat too for sealing.

Pics of it painted black with Rustoleum spray, the large silver professional cans, that dries in 15 minutes.
I have to tie the nylon fuel lines to the brake line as when it was replaced some time ago, those plastic holders were removed. They were impossible to get too anyway.

https://photos.app.goo.gl/Q85WXBE8mdV2Doiw8

https://photos.app.goo.gl/c34Zd7cEJiC3sasp6

The areas under the mufflers are pretty rusty. One of the shields has corroded and fallen onto the muffler. I am not up to taking out the exhaust to attempt scrapping off the area and coating it.
The other side floor pans are very dirty and greasy and have not rusted much, but I did fix the far edge where it starts going on top of the frame.

Make sure you kill the rust first with phosphoric acid etching or POR rust converter or some such treatment.

Rust converter is not needed with this glue. But it wont hurt.
I have found it sticks very well. The difference is this coating is waterproof, so putting it on dry rust, the rust is stable. Paints let moisture through, causing more rusting under the paint.


the glue wont work if waxes, oils, greases, dirts, wetness, loose rust exists on the metal surface. the metal must be dry and reasonably clean with tight rust. the glue will stick to clean  factory paint.

Use a cheap brush and forcibly smear it into the surface. Go over it a second time after it cures if it needs it. Let it cure overnight, it will form a hard rubbery slick feeling surface. This glue swells as it cures, which is a good thing. It forces itself further into cracks.
the surface needs no primer for paint.

You can tell right away if it is not sticking to the metal, it will peel off easily after it cures.