These pictures show the corrosion around the bottom of the sides of my Merc 709D. As you can see I have folded down a section of the outer skin. I can fabricate a replacement quite easily from aluminium, but I was wondering what hints and tips the team might have. In particular regard fixings, corrosion-proofing, and painting.
Bill
Won't your aluminium replacement become a sacrificial anode?
A lot of this problem is caused by galvanic action. ie mixed metals. (Plus water)
All you can do is make a repair and I suggest coating with this stuff or similar.
Good stuff.
That looks horrible. Looks like you'll soon be in a Triggers broom situation, cutting out the rot and welding in new metal.
Philip
Apart from the fact that using (bonded/rivetted/bolted) ally as a replacement for that welded stressed steel would be an MOT fail, it's just crying out for electrolytic corrosion.
Cut all the rot out, weld new steel in. Weld-through primer on the inside of any seams, then plenty of schutz and wax when it's all back together.
And give a thorough bollocking to the numpty that shoved it full of podge and mastic in the first place, instead of fixing it properly when it was a minor issue.
That's what you can see, it could be as bad or much worse elsewhere. You should have had the cavities and the underside regularly treated with a decent rust proof treatment (Dinol not Waxoyl)
It's structural, if you can't get a proper replacement welded in then it's f*cked.
Alternative course of action:
Check insurance cover Alibi Can of accelerant Rag Match
Since that looks to be structural, the only decent way to repair it is by letting in new steel of the same gauge as the original.
The obvious place to do this would be one used to restoring classic cars etc. 'MOT standard' welding, which should be cheaper, usually involves plating over the corrosion, which doesn't tend to last long, as the old rust attacks the new steel in short order.
So the correct method is to cut out all the rust to good metal, fabricate a repair section which butts up to the edges, and seam weld all the way round. (The best way is to stitch weld first to locate it properly, then do the seam a little at a time to prevent excess heat causing distortion.)
If it's a panel which shows, you'd then grind down the weld flush and paint. Properly done it will be invisible and as strong as the original.
If the repair involves spot welds (two faces meeting, etc) both faces should be cleaned to bright metal then a weld through primer used - as it is near impossible to protect this sort of joint afterwards. Where the two panels meet should be sealed with seam sealer after welding.
As regards protecting the inside of a box section etc after repair which usually can't be painted, I favour Dinitrol LM which is thin and penetrates cavities well. Can be bought in aerosol form for small (ish) areas and with a long tube to access down the box section. Then after a couple of days, Dinitrol 1000 which is more of a traditional wax.
If you have a lot to do, it's cheaper to buy it in a container and spray it in - if you have a compressor.
In article , Bill Wright scribeth thus
Looks to me Bill that you'd make a much better job of it by welding in steel rather than patching with Ally. That does look on the structural side and I reckon you'd not be far amiss on that by asking a friendly MOT tester if he'd pass that like that patched up if you have one;!.
Also that does look like its quite bad and asks the question what's the rest of the wagon like if its much the same makes me wonder if its come to the end of its useful life...
Fixings: continuous weld. Nothing else is going to satisfy the MOT where its structural.
Corrosionproofing: epoxy firstcoat is an excellent plan. If you use waxy oily gloop, waxoyl scored bottom of the list when I saw some tested.
Metal: use steel not ali. Ali & steel really dont mix.
These things are always worse than they look.
NT
It's not clear to me that this area *is* actually structural. Being a comm ercial vehicle, it's not exactly of a monocoque construction like the vast majority of cars. It probably has a rather heavy box section chassis-like construction, with the floor forming the top surface of the box sections.
My 1980s Bedford CF panel van-based motorhome had corrosion very much like that shown in your photos. The corroded "sill" panels certainly weren't st ructural. I "repaired" them using fibreglass mat (in my case, I chose wove n) and painted the whole bottom 12" a bright yellow colour. With some matc hing coachlines, the whole van actually looked very smart. And no MOT gara ge had a problem with it for the fifteen or so subsequent years of its life .
By the way, I concluded the corrosion was caused by poor fitting of the mot orhome windows. The van panels had holes cut out, and aluminium-framed win dows fitted, but they hadn't properly sealed the windows in. So any rain r unning down the side of the van found its way to the inside of the panel an d ended up collecting in the "sill".
I wouldn't bet on it. With vans, the rear structure of the box van is often VERY different to the rear structure of chassis-cab equivalents intended for coachbuilders. Much more similar to a traditional monocoque.
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