How to stop and cover up aluminum corrosion on the exterior?

[Jnbroadbent]

With some of the nasty rusting from the inside braces (the ones a few inches above the floor) it caused the aluminum panels to corrode, with a handful of small holes. First train of thought is to replace but maybe there are some alternatives that would be a whole of hell lot easier. Anybody have any thoughts on this?

[chessie4905]

you could try product from this company to arrest further damage:

http://www.saltx.com/index.htm

[rv_safetyman]

Welcome to the forum.  It would be great if you would set up a signature with at least your first name, type of bus and location.  That way, we might be able to help you better.

The first thing we need to know is the type of bus.  Second thing, pictures would be great.  I assume you have access to the inside where the corrosion is taking place.

You need to stop both the steel and aluminum corrosion (steel takes something like "metal prep" and aluminum takes a different solution - we used to use a product called "Alumaprep" or something like that).   Then, you need to use some sort of special aluminum primer on both sides of the affected area.  If you could find zinc chromate, that is the best, but I think the EPA made them take it off the market.  Someone recently noted that it might be available from a marine supplier.

Depending on the amount of damage, you could try to clean out the holes, and use fiberglass to fill the holes.  I would not use Bondo,  You could try the Bondo with fiberglass fibers.  Before you apply the filler, you should use something like a ball peen hammer to indent the hole so that you have a good surface to grip to.  Again, this approach depends on making sure that the corrosion has been arrested and the surface properly prepped.  I think it is best to put the fiberglass material over the proper primer.  We always prepared steel surfaces with PPG DP40 before applying Bondo.

SaltX is great stuff for protecting against salt damage.  Lots of Bonneville folks use it.  I am not sure that it is the correct product for this application.

To do it right, I would visit a GOOD automotive paint supplier and see what they recommend for the treatment, primer, and filler products (the industry has changed a ton since I was involved).

Jim

[TomC]

I have a '77 AMGeneral transit bus with steel wall and ceiling beams with aluminum sheeting over.  In the 35 years, there are only a couple of small spots where there is aluminum corrsion-and I'm not to concerned with them.  Why-because ALL surfaces that interface between steel and aluminum are insulated with a mylar insulating strip-not allowing the dissimilar metals to touch.  And then either aluminum or stainless rivets were used.  Just priming both surfaces will work for awhile, until the primer rubs off and then the corrosion begins again.  To truly stop corrosion, you have to separate the metals completely with some sort of insulating material. 

On my truck conversion, a similar system is used. The aluminum skin is attached to the steel beams by 3M tape.  Again-no contact.  Good Luck, TomC

[gus]

The only thing I know that will actually stop corrosion, even battery acid corrosion, is Corrosion-X or Boshield. There are a couple of others but I don't know the names.

These are made for aircraft use and work. I used Corrosion-X for years on light aircraft. It is oily and will seep into all seams anywhere. However, don't use it before you do the repair work because nothing will stick to it.

If the metal is not too damaged you should squirt CX into every nook you can find and redo it about every six months. If it needs repairing use CX after the repairs are done.

I used it in my battery box after giving up on keeping it clean and it now has dead corrosion salts in it but nothing is corroding anymore. I also use it on all vehicle battery terminals, light coating is all that is needed.

[Jnbroadbent]

Welcome to the forum.  It would be great if you would set up a signature with at least your first name, type of bus and location.  That way, we might be able to help you better.

The first thing we need to know is the type of bus.  Second thing, pictures would be great.  I assume you have access to the inside where the corrosion is taking place.

You need to stop both the steel and aluminum corrosion (steel takes something like "metal prep" and aluminum takes a different solution - we used to use a product called "Alumaprep" or something like that).   Then, you need to use some sort of special aluminum primer on both sides of the affected area.  If you could find zinc chromate, that is the best, but I think the EPA made them take it off the market.  Someone recently noted that it might be available from a marine supplier.

Depending on the amount of damage, you could try to clean out the holes, and use fiberglass to fill the holes.  I would not use Bondo,  You could try the Bondo with fiberglass fibers.  Before you apply the filler, you should use something like a ball peen hammer to indent the hole so that you have a good surface to grip to.  Again, this approach depends on making sure that the corrosion has been arrested and the surface properly prepped.  I think it is best to put the fiberglass material over the proper primer.  We always prepared steel surfaces with PPG DP40 before applying Bondo.

SaltX is great stuff for protecting against salt damage.  Lots of Bonneville folks use it.  I am not sure that it is the correct product for this application.

To do it right, I would visit a GOOD automotive paint supplier and see what they recommend for the treatment, primer, and filler products (the industry has changed a ton since I was involved).

Jim

Jim,

   Thanks for a reply! I've updated my sig with all my info. Good call!

It's a mc9. Most of the horizontal steel braces that are about 8-10" off the floor have been rusting. Seems like the aluminum would sweat, the moisture would then sit in the fiberglass and thus rust. The supports under the windows and vertically are in great condition so it seems like that's the only culprit.

The previous owner tried to fix it with bondo but the paint over it quickly bubbled up. They didn't fix the cause, just a quick patch. Didn't even think of Fiberglass. I could fiberglass it from the inside then maybe the bondo w/ fiber on the outside. I will do some more homework.

Thanks again everyone!

[Charles in SC]

I recently bought Zinc Chromate from Aircraft Spruce. They also have Zinc Oxide which is the new EPA friendly stuff. The yellow covers better.

[Utahclaimjumper]

 Zinc chromate is now virtually useless,, all zinc has been removed from it,,,thanks EPA!!  For any corrosion to form or progress, AIR is neccessary,, clean and prime all surfaces with poli eurathane primer and paint with same. No air contact, no corrosion,period..>>>Dan

[luvrbus]

Why not cut the section out and replace it they have aluminum rods now about anyone can use with a small propane torch,I done it on boats with a tig welder before back in the day when that was the only option   

[gus]

If you use yellow Zinc chromate don't put it on too thick. The old formulas  called for thin coats so the ZC could do its job, thicker actually made it less effective.

The newer stuff may be different so check the label.

[Jnbroadbent]

Bought some of this

http://www.homedepot.com/buy/klean-strip-1-gallon-phosphoric-prep-and-etch-gkpa30220.html#.UOXivKUmA7c

We'll see how it works over the weekend.