Fixing rust on the bottom

[tscinmd]

I crawled under my 80 dl hatch to see what kind of shape the bottom was in today before we started the motor work this weekend. discovered a few places that need fixed. One, there is a baseball sized hole in the rear passenger floor that has been patched with a sheet of thin metal. The patch isn't welded in, just screwed. There is also a small hole in the bottom next to the jack point right behind the passenger front wheel. I'm going to see if my gf's brothers can weld them up for me and fix them for good. Other than those two spots, the other rust seems to be surface rust on the bottom. What do you guys suggest as an undercoating? Should I go all out or just rustoleum the bottem every so often?

[the_bard]

Next Subie I pick up, I plan on going over (under?) the bottom with a finetooth comb, looking for rust spots. If I pick up any surface rust, I plan on knocking as much out as I can, then applying POR-15 over it... then probably that rubber undercoating crap I keep seeing at *Mart.

 

I'm even considering picking up the high-temp POR-15, and covering the exhaust system, if I ever decide to build one from scratch.

[85Sub4WD]

speaking from expierence - rubber undercoating isn't that great -

 

it prevents water from meeting metal under ideal circumstances; but it also can trap water and make rust MUCH worse - hence why most newer cars don't have it

 

 

FIX THE SURFACE RUST NOW - use something rust-oleumish and you should be fine

[Ross]

Idealy you want it galvanised - thats a little drastic though. There are paints available with a high zinc content in them - they will provide galvanic corrosion protection like galvanising. You might want to look in to something along these lines.

[85Sub4WD]

Idealy you want it galvanised

EXACTALLY

 

Most new cars over here are galvanised - hence why rustproofing is unnecessary

 

didn't know about the high zinc-content paints - will have to look into that further (most of my family's cars were made before galvanizing cars was common, and therefore have great rust potiential) - thanks Ross

[Ross]

No prob.

In new zealand there is a range of these zinc paints available with varying zinc contents. The one i have has something like 98% zinc, so should work well. Its canned by someone in austrailia, so you wont be able to get the same brand, but you should be able to find an equivalent.

[tscinmd]

I'll have to look into that ... I was never really keen on the rubber stuff either - when I bought my old VW Golf back a few years ago, I pulled all the rubber stuff off. Luckily , there was no rust. I just lightly sanded and sprayed the hell out of everything that didn't move. Sold it last year and it still doesn't have a trace of rust on it. It sucks with this subaru because the upper body is fine except for a small nickle sized hole in the drivers door. I guess I can't expect a perfect car that is 25 years old. I just hope this project becomes a good reliable car. I just offed my 95 escort GT ... pulled the tags off of it yesterday and dropped the insurance. Was a good car, but it's time had come. We have a 2003 Suzuki Aerio AWD to get around in, but I can't wait for the Subie to be finished. I'll post some pictures after the motor gets swapped in this weekend.

[thealleyboy]

I always "prime" treated rust areas with Extend, and I think this helps the rubberized undercoating stick better. The two systems are totally compatible, and I have had good experience doing it this way.

 

I have never tried the zinc paints, but it sounds like a good choice for underbody. My only concern would be neutralizing the rust that had already taken hold (pitted metal). What is the best way to prep the rusty metal before using zinc paint?

John

[idosubaru]

i have no idea what it's called but i have some spray on solution that someone gave to me. i had it sitting around and didn't expect much from it. i pulled a motor out of my daily driver XT6 just a couple weeks ago that i'm doing some work on and decided to hit the lower radiator support with this stuff since it was rusted. i should have taken before/after pictures. wire brushed it and got all the loose rust flakes off. then sprayed this clear liquid (basically looked like water when applied) all over the lower support. the next day all the rust was *gone*, it was a silver color and this bottle makes claims that it neutralizes rust. looks real nice, i plan on painting it and using this stuff some more on the underbody as well before applying some high quality paint. i'll post pic's and the name of the stuff if i can remember to go look. i often miss lots of posts so PM me or remind me to post back if anyone is interested.

[karinvail]

go to an auto paint store and get some 'rust converter' (not the spray on junk). It's a paint on liquid that stops rust and changes it from rust colored to black (it's a chemical reaction, and it goes through different colors as it dries). Hubby and I used this on the tracks of his snowcat and it worked FANTASTIC!

[thealleyboy]

Gary:

There are several products that supposedly neutralize rust. POR-15 has an excellent reputation with the classic/restoration crowd. It's also very expensive. I'm planning to use it on my 67 Mustang project cause I know it will hold up for many years.

On my Subes, I have been using Extend. It is fairly easy to come by, inexpensive and works well. I'm sure some of the others are good, but I'm sold on Extend for routine rust repair work.

good luck, John

[tscinmd]

Where do you get extend. I was planning on using Por 15, but that stuff costs more for a gallon that I have in the car lol .

[thealleyboy]

Where do you get extend. I was planning on using Por 15, but that stuff costs more for a gallon that I have in the car lol .

 

 

I have seen Extend, in both spray and brush-on form, at NAPA. Some Lowe's stores also carry it. If you can't find it at those stores, you might try some old-fashioned hardware stores (True Value, Ace, etc).

Extend gives you a lot of bang for the buck. As with any rust work, you need to do a good job of prep if the repair is to hold up over time.

good luck, John

[idosubaru]

the product i used is called Oxisolve. it was left in the trunk of a car i bought, never heard of it before. cleaned it off and sprayed it on my lower radiator support just for kicks (engine and radiator all removed). next day all the rust appeared *gone*. it had turned dark gray/black, i guess that's a good thing? don't know.

 

some body work people mentioned these products:

http://www.safestrustremover.com/

 

http://www.cleanrust.com/rustsolveworks.html

 

i've also read that some of these products may weaken the metal or the rust may return later. dont know what to believe, i suppose if cleaned and prepared properly it seems these products may indeed work. of course rust will return later if you don't do a thorough job.

[thealleyboy]

Gary:

 

Rust is what weakens the metal. Anything that will slow down (if not stop) the deterioration is good for the car.

 

IMO, it's a matter of how far you want to go with rust control. It's easy to go overboard and attempt to eliminate rust once and for all. This might be feasible for a "classic" type vehicle - but probably not for the majority of cars we are talking about. An exception might be the xt6. I plan to do a fairly thorough restoration on my 91, and this will involve some metal replacement, as well as lots of treatment with POR.

 

A more realistic approach is to control the deterioration so that the car will live out it's useful life. This means all the major systems of the car should wear out at roughly the same time. Any of the lower cost rust converters, along with some elbow grease, will put the brakes on unibody deterioration.

 

There is no honor in hauling off a car to the junkyard that looks good on the outside - but is rotted out structurally.

 

good luck, John