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Rust proofing newly welded closed sections
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rcx822



Joined: 31 Dec 2010
Posts: 27

PostPosted: Sun Jan 02, 2011 8:33 am    Post subject: Rust proofing newly welded closed sections Reply with quote

I am looking at welding up some sections which will then be inaccessible inside in order to paint and rust proof them from the inside. I've done some Googling, and found tutorials that recommend painting the parts with weld-through primer and then welding. But doesn't that leave the weld exposed to rust?

I am thinking of drilling some access holes and then finding some nozzle that can fit in an paint the inside.

Any advice on the subject appreciated.
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buzzy bee



Joined: 23 Nov 2007
Posts: 3400
Location: South Cheshire

PostPosted: Sun Jan 02, 2011 11:53 am    Post subject: Reply with quote

Hi

Galvanise it, or dip it, or electrostatically paint it, or drill holes and wax it.

Cheers

Dave
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Bellisin



Joined: 19 Dec 2010
Posts: 19

PostPosted: Wed Jan 05, 2011 7:27 pm    Post subject: Reply with quote

The weld through primer is good in that it will give protection without interferring with your weld. It can also help the welding a little too. Nevertheless it will burn away around the weld and of course the weld material itself will not be protected.

I would use the weld through primer but then waxoil the cavity afterwards. The weldthrough will protect any gaps in the waxiol protection whilst hopefully the waxoil will cover the newly welded metal.

I hope this answers your question.

Stuart
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baconsdozen



Joined: 03 Dec 2007
Posts: 767
Location: Escaped to Gorleston

PostPosted: Thu Jan 06, 2011 1:09 pm    Post subject: Reply with quote

If spraying waxoyl or whatever inside a box section make sure you get plenty of it in there.Any area thats not covered will rust far quicker thand if the whole lot had been left untreated.
Some while back I spent some time testing various anti rust paints etc (coming to the conclusion that one very well known paint is worse than useless) and asked some of the off shore companies what they used. A large flat steel sheet does suprising well if untreated but any paint,grease or oil (other than a sacrificial system) that leaves areas bare simply makes things worse.
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ukdave2002



Joined: 23 Nov 2007
Posts: 2332
Location: South Cheshire

PostPosted: Sat Jan 08, 2011 8:51 am    Post subject: Reply with quote

The original Mini's had the inner and outer sill void filled with expanding foam, reputably the sills on these cars on these cars outlasted the later non filled by a considerable factor. I have no idea why BMC stopped doing it, neither am I aware of any other vehicle manufacturer using this process?

I kinda get the logic; in a box section condensation will always form from the air and its this that causes the corrosion rather than water seeping in. By filling with foam the air is mainly removed so condensation is almost completely eliminated. The type of foam used wont absorb water either.

I suspect there is a good reason why its not a more commonly used process, anyone know why?


Dave
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Kelsham



Joined: 18 Jan 2009
Posts: 349
Location: Llandrindod Wells Powys

PostPosted: Sat Jan 08, 2011 3:59 pm    Post subject: rustproofing Reply with quote

Back in the late 1960s I fancied myself as a car dealer and began to specialise in buying selling and repairing Mini's.

One Mini I bought had rusty sills, I tackled the repair with some sills I had made up locally.
I was surprised to find the foam filling. It obviously had failed on this car.

BMC soon stopped injecting it. I would assume that as the car I was welding was only about 8 years old ,that the experiment with foam was a failure.

It was dificult to remove to carry out the repair. Lots of fumes.

Regards Kels.
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baconsdozen



Joined: 03 Dec 2007
Posts: 767
Location: Escaped to Gorleston

PostPosted: Mon Jan 10, 2011 10:55 am    Post subject: Reply with quote

Same problem,if damp gets in behind the foam anywhere it will start localised corrosion faster than if the panel was exposed to the air.
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