Pinhead holes in Aluminium

[bonfireboy]

My CI built van dates from the mid 90's and I have had to replace / rebuild the roof as it was developing small (1 or 2 mm diameter) holes. A metallurgist told me they had seen this when part of the aluminium was in contact with raw steel - not sure how true this is.
Now similar holes have appeared in the sides - I have found one which clearly has been there from day 1 as the paint which had filled the hole was still there but flicked out to allow me to seal the space.
Has anyone else experience with this? Any suggestions as to what can be done other than maintain vigilance and seal as necessary?

 

[nrdonnelly]

Hello Bonfire Boy - only just seen this - sorry for the very slow reply.

I had this problem on an Avondale caravan I was fixing a few years ago - the aluminium had gone into pinholes where some moisture got into the wall. With vinyl-covered wallboard on the inside, the moisture decided the easiest way out was through the wall.

Steel will cause a similar reaction but there isn't much of that in contact with the walls in most vans. I suspect it is more likely a reaction to the adhesive used in the walls in manufacture, or as I say in my case, damp.

My fix was to put a strip sellotape over the holes on the outside of the van (sounds ridiculous, but bear with me)

Then, I stripped the inside of the van back of the wall to clean off the white corrosion on the back of the skin, and then to lay a piece of fibreglass matt across the back of the wall, laid on fibreglass resin and pushed firmly into the skin of the van. The Sellotape stops the resin oozing out through the pin holes.

Once this had all dried, I reassembled the inside of the van. Outside, I used a touch-up paint pen to cover the pinhole damage. The fibreglass is great because it protects and reinforces the skin of the van, and is completely non-porous, so stops moisture getting in.

It was slightly different on the caravan as I was dealing with a smooth-skinned van, rather than a stippled effect, but the latter makes it easier to hide the damage on the outside. Also, if the holes are caused by a little moisture in the walls of the van, it's important to figure out where and reseal the problem area to stop the same thing happening again.

Hope that makes some sense!