I have been working on a little bit of rustoration on my 72 subie conversion, and found a couple of areas that have some of the dreaded 'rust bunnies'. One of these is just behind the doors, just on the inside of the vent tube, and the other is by the taillights on toward the outside of the car. after looking at and repairing these areas, i think that the best way to protect them is to keep all of the road grime and moisture out. My thought was to take some 2 part expanding closed cell foam and fill these spots. I found three products on 3M's website that look like they would work. Does anyone have any experience with these products? Foams and NVH

Thanks in advance
Thomas

The factory foam is what made those areas rust in the first place ...

It works great until it cracks (and it will crack eventually). Then, it becomes a huge sponge that traps moisture.


I think the foam is a bad idea ...

If anything, the NVH material would look promising as it stays pliable. If it turns hard with age, the scenario Andy stated could be true.

Was the factory foam closed cell?

The foam would eventually be just another place for water to collect.

aside from the factory foam MAKING rust conditions prime, it will warp any body panels... my lesson on another car

Gosh, what more can you say. Every where the factory put it it rusted.... Let it berath, let it drain.

foam in sheet metal cavities = future rust hole

Some guy did this to his Nova on one of the Musclecar forums a few years ago, and rusted the thing out horribly. You'll be sorry. . .

I understand that done improperly the foam can act like a sponge, however all of the foam in the car is 38 years old, and seems to have done a pretty good job. On my car i have one corner that still has the factory foam in it, and one that it was removed to replace the fender a number of years ago. The one that was replaced is now full of road grime, sand, pebbles and the like, and beginning to rust, while the factory foam is still rust free and solid.. It would seem to me that done properly, and sealed, i would be miles ahead of a bunch of sand in that corner.

Further thoughts?

if you do it, you have to be positive that you have ALL the rust that is there now out. once you foam it, you can't get at the rust that starts to form under it.

Up near the vent tube at the door handle does not seem to be foam, but just a whole large pile of seam sealer.
The foam in the targa bar certainly absorbs moisture...quite a bit and eventually is starts rusting the top of the fender just below the targa bar intersection.

I think the foam, properly done and very very well sealed with a waterproof membrane (like seam sealer) would be fine for another 35 years.

One thing to consider...you will never drive this car like you would have if it was your new car...it will get better care, and you will hose out those areas each year at least.

We are seeing 40 year old cars that have not been properly cleaned in decades...and they lived outside for a large portion of time.

SOme of the guys here with cars they have owned forever have not experienced the same rust issues as those of us that purchased a 3-4-5th hand car.

Another modification that I consider manditory is to put 1/4 inch or 3/8 inch rubber washers between the rocker covers and the long on the bottom fasteners.
In the original design, the dirt and crap has no place to go, then it builds up. If you use the rubber washers as standoffs you cant see the difference (unless you crawl underneath and look) and you can stick a hose in both endfs of the rocker cover and blow out all the built up crap.

Alot of the sand will just fall out naturally.

To you original point, go for it.
Just create a super sealed section so water can never get to the foam.
I have sections over the rear tailights that the metal is still bare and pristine once the foam was removed.
I have had other cars that in that same area the sealant pulled away and the foam made the issue much worse when wet.
Rich

This thread makes me think or Firestone radial tires. These steel belted tires went bad in a bad way. The steel would rust inside the rubber and the tires would come apart later. The problem was that they used a slurry like material on the steel belt just before placing it in the mold. The container was open to the air and absorbed moisture. This caused the belt corrosion. Since some of our cars had a problem more than others, I cannot help but wonder if a similar condition happened here. Maybe the foam got contaminated. It also could have happened to cars that were made on more humid days.

I would leave the stuff out just the same.

Yes ...

I have the exact same scenario on my car, but with the opposite results.

One rear fender was replaced at least 15 years ago and no foam was installed. The other side still had the factory foam.

When i did my rust-o-ration, the side *without* foam had no rust what-so-ever in the cavity over the taillights.

The side with the factory foam looked *ok* initially. The foam looked solid and there was some sort of seam sealer around it with undercoating on top.
Once i started digging out the foam, the foam had rust sticking to it! When i was done removing the foam, i found that the area right above the tail light was paper thin with a few pinholes in it. It had rusted from the inside out.

The foam *looked* solid before i removed it, but it wasn't. The other side, without the foam, had the opportunity to dry after it got wet.

Does that area collect dirt? Sure it does. That's what a pressure washer is for. A solid coat of paint and a occasional pressure wash will go a long way to keep the rust away.

I don't think foam is the right answer ...