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Some rust treatment questions
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rcx822



Joined: 31 Dec 2010
Posts: 112

PostPosted: Mon Sep 19, 2016 9:36 pm    Post subject: Some rust treatment questions Reply with quote

Hello again.

Is there any secret for dealing with profiles of a car body that are too small to fit a wand into to get rust inhibitor in there? I've got such "double skin" sections and one of the skins has rusted. It's the inner skin that's rusted so I was thinking of rewelding it leaving a bigger gap to be able to fit a wand inside.

The car has some seams that are starting to blow but are still structurally sound. Some rust has started to form inside the seams and is starting to push the seam apart but it's still in early stages. The seam sealer has of course failed and let this happen. If I reseal these seams, trapping the rust inside, will that stop the rust spreading for so long as the new seam seal is working?

I've read good things about POR15 paint, which, although it was designed to go onto rusty metal, there is a primer that allows it to go onto bare metal. Do we prefer POR15 over a two part paint like Rustbuster Epoxy Mastic 121 which can also be brushed on?

I was thinking of having the chassis hot dip galvanised. I know there's a risk to this but replacement chassis are easily available (though all rusted) so I thought I'd risk it. As it's an aged chassis, I assume it will need to be stripped before being galvanised? Which method is favoured and which method is cheaper? A caustic dip, or pyrolysis?

Thanks for the help!


Last edited by rcx822 on Tue Sep 20, 2016 11:16 am; edited 1 time in total
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MikeEdwards



Joined: 25 May 2011
Posts: 2466
Location: South Cheshire

PostPosted: Tue Sep 20, 2016 11:04 am    Post subject: Reply with quote

I read that POR-15 is intended to stick best to rusty metal, presumably because of the pitted surface. I have used some in various places, and did find (not unexpectedly, once I later read up on it) that where I'd painted it on some new metal against masking tape, when I removed the masking tape it also brought some of the POR off like a skin, leaving no sign it had ever been there. I believe that's the idea of the primer, is to make it adhere on smooth clean metal. I've used Epoxy Mastic on the whole underside of the car, and found it to stick better. Smells horrible while you're painting it, though.

As for cleaning rust out of areas like spot-welded seams, you have two challenges - one is knowing that you've cleaned the rust out, and the other is knowing that you've put something in place to stop it coming back. Without opening the seams you can't "know" either of those things, so it's down to how much work you want to do to be sure. I've had areas where my "chassis rails" (it's monocoque, but it's easier than writing "longitudinal strengthening members" all the time) are spot-welded to the floor and you can see rust is spreading the joint, so I've cut that section out, treated the remaining part and replaced with new steel, choosing whether to cut chassis or floor depending on where the most damage appeared to be, and sometimes doing both.

I've painted with weld-through primer before assembly, put seam sealer on before the stonechip, and will pump waxoyl into the box sections when I'm 100% certain there's no more welding to do. But I can't say how effective it will be. One issue I found is that where the two pieces of steel meet, there was no paint at all - where the seam sealer hadn't failed was bright shiny metal, but unfortunately where it had failed was very rusty as you'd expect.

Some of the newer rust inhibitors (Dynol I think is one) make a big thing of how far they'll penetrate into seams and narrow areas, but I haven't tried them myself. I have visions of penetrating through the welded repair and coming through the paint on a hot day.
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Paul fairall



Joined: 17 Nov 2016
Posts: 429
Location: North west Kent

PostPosted: Sun Jan 08, 2017 10:42 am    Post subject: Reply with quote

Just bought Granvile heavy duty rust cure from Frost Automotive, por15 is not good to paint over. Phoned Frost and spoke to technical and he suggested Granville. Will see how it goes.
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