Rear door shut rust (split from Merlyn's blog)

[mat_fenwick]

I'd suggest that's better than most. For a permanent repair (well, at least as long as the original lasted) the rust between the layers needs to be removed, and the rear panel welded back on, and re-sealed. For a medium term repair (several years) wire brushing back to shiny metal and working a phosphoric acid based rust remover into the seam will slow it down a lot. Mine was in a similar state about 8 years ago, and this treatment, repeated every few years means that it's only this year I'll have to think about cutting out and welding it.

Chances are it's a crack in the sealant behind the wheelarch which is letting water between the layers, so if you can find that and rectify (or at the very least spray lots of waxoyl around which will help seal it), that will also help.

[merlyn]

I have also noticed a very small bubbling of rust on the rear side panel near the fuel cap. I guess taking that back to metal would be advised too. With the door sills should I be trying to do both sides of the metal, on top and underneath, although I'm sure that will be really difficult. I will need some advice on respraying when the time comes. I tried dealing with rust on the doors of a Fiesta years ago but it only ever lasted about two months before it came back.

[Paul296]

Regarding the rust, I'd suggest that's better than most. For a permanent repair (well, at least as long as the original lasted) the rust between the layers needs to be removed, and the rear panel welded back on, and re-sealed. For a medium term repair (several years) wire brushing back to shiny metal and working a phosphoric acid based rust remover into the seam will slow it down a lot. Mine was in a similar state about 8 years ago, and this treatment, repeated every few years means that it's only this year I'll have to think about cutting out and welding it.

Chances are it's a crack in the sealant behind the wheelarch which is letting water between the layers, so if you can find that and rectify (or at the very least spray lots of waxoyl around which will help seal it), that will also help.

Assuming you meant the door shuts Mat? One side doesn't look too bad to me, but the other looks like you might have a hole once it's all ground back (ouch!) - I'd get it treated asap, certainly before the winter; it grows at an alarming rate!

Is 'Kurust' a phosphoric acid based rust remover Mat? If it isn't what is, and is it better than 'Kurust'?

[mat_fenwick]

The last time I used Kurust it was phosphoric acid based, but now it appears to have changed to a tannic acid solution. Whether this is better or (more likely!) safer I don't know. I've found the liquid types better at penetrating rust than the gel types. A quick test you can do is to apply to an area of 'surface' rust, allow to change colour and then start sending back the converted rust. How long before the converted rust is sanded away and unconverted rust is revealed? That will show you how well your chosen converter penetrates into the rust.

That said, I'm not trying to say there is 'only one true way', it's a bit like tyres and engine oils - we all have our preferences and want to believe that our way is the best way for our own peace of mind! I don't have any evidence to say a phosphoric acid based one is the best one, just that's what I know has worked for me. But not as long a term solution as mechanically removing all rust and painting. If someone has found a rust converter that they have painted over rust and it has remained rust free for say 10 years, I'd be very interested! (and slightly suspicious...)

EDIT - Anyone got $10?

[Paul296]

EDIT - Anyone got $10?

Thank for that Mat. I'll print it off and save it for, er . . . lent

I never really just 'treat' rust but grind it all back to new metal. I apply a rust treatment as a sort of 'belt and braces' just in case type of thing. In my experience NOTHING treats rust; even if it looks treated on top it's still going mental underneath! That phosphoric acid thingy (what you said!) just sounded impressive - I'm always looking for a hot tip from someone with a bit more knowledge and experience than myself.

When you were on about waxoiling, did you mean the weld seam inside the wheel arch?

[merlyn]

Looks like I'll be spending a few weekends sitting on the curb outside my house with pack of wet & dry and a load of chemicals, and coffee! I'll start with the worst one first, do you think I'll get enough of it off without a grinder (which I don't have) and if there is a hole in there what then? Will that mean some welding even if it's just a small hole?
Please forgive my ignorance, I haven't got much of a clue and I want to get it right. Maybe I should leave the worst one until I've had some practice.

Cheers, Jane

[Caffiend]

In my experience NOTHING treats rust; even if it looks treated on top it's still going mental underneath!

Results of this research indicate that all formulations including the commercial one are ineffective in reducing the corrosion rate when applied on initially cleaned low carbon steel. Initially rusted low carbon steel samples treated with either phosphoric acid or a mixture of phosphoric and tannic acids resulted in the lowest corrosion rates (about 3 mpy) when tested in a simulated weathering chamber.

First version more comprehensible, but I think I'll save my 10 dollah - the bottom line seems to be that whatever you do (treat it or just sand it) will only slow it down until you can get it made like new by an expert.

Jane, get yourself to Wetherby on Sunday - I know it's a couple of hours drive for you, but will really be worth it to meet a few people and soak up some learning . Also, I'm sure Paul would be happy for you to join me in class (my TZD is starting to go in the same place-door shuts-as well as having a few other nicks and dings that I really want to get sorted before the rust sets in) and Paul has v kindly promised me a tutorial in return for flapjack (which may mean I have to sacrifice car washing for cooking on Friday, but sure it'll be worth it).

[merlyn]

Jane, get yourself to Wetherby on Sunday - I know it's a couple of hours drive for you, but will really be worth it to meet a few people and soak up some learning . Also, I'm sure Paul would be happy for you to join me in class (my TZD is starting to go in the same place-door shuts-as well as having a few other nicks and dings that I really want to get sorted before the rust sets in) and Paul has v kindly promised me a tutorial in return for flapjack (which may mean I have to sacrifice car washing for cooking on Friday, but sure it'll be worth it).

I'm really tempted to try to get to Wetherby, I'd love to do a couple of hours driving in my new car, of course it would be another couple to get back and that may not be as much fun when tired. Not sure the family will be as keen though. My partner lives in London and only gets one weekend in two here with us and I doubt he would want to come along (not into cars at all, never mind BXs) and he might be offended if I choose to go off and leave him on Sunday!

I will have to ask everyone and see what they think. Watch this space. (ICCCR looks like being out of the question as we are booked to be camping in Leicestershire from 9th to 19th August)

Jane

[mat_fenwick]

I never really just 'treat' rust but grind it all back to new metal. I apply a rust treatment as a sort of 'belt and braces' just in case type of thing. In my experience NOTHING treats rust; even if it looks treated on top it's still going mental underneath!

Agreed. I think that even when back to shiny metal chances are there will be a bit (maybe microscopic) you've missed, or is in a seam so treating it should help.

Jane, for awkward corners I find a wire brush easier than sandpaper - ideally one mounted on an angle grinder or second best, a drill. If you do find a hole then it's not classed as structural for the MOT so fibreglass/filler would be an acceptable repair in that respect. The problem with filler is that it absorbs moisture (or at least used to - things may have moved on!) and so can promote rusting, especially if not sealed from behind. Welding is a more long term repair, but even that needs good protection to last as long as the original, as it won't have the dip treatment that Citroen initially gave to the whole bodyshell.

Paul, yes I was meaning the seam inside the wheelarch. The rubbery coating that Citroen used is a bit of a double edged sword as it lasts well, but if/when it does crack, still remains mostly visibly OK so rust can be creeping behind unnoticed. Waxoyl or similar should at least seal any cracks to at least stop more moisture getting in but obviously needs to be done during a period of dry weather!

[Paul296]

Paul, yes I was meaning the seam inside the wheelarch. The rubbery coating that Citroën used is a bit of a double edged sword as it lasts well, but if/when it does crack, still remains mostly visibly OK so rust can be creeping behind unnoticed. Waxoyl or similar should at least seal any cracks to at least stop more moisture getting in but obviously needs to be done during a period of dry weather!

Thanks for that Mat. That explains A LOT. When I repaired my door shuts about 6 months ago, I had the wheels off, cleaned out all the wheel arches, hairdryered it to remove any residual damp then coated all the seams with waxoyl. Result; the repair is still sweet as a nut. A few months later I carried out the same repair on Mulleys TXD (forgetting to waxoyl the wheel arches) and within a week rust had started to become visible again. Next time I mosey on down to Clay Cross I'll put some waxoyl in my saddle bag I think!

Jane; Here's the repair I did to my TZD last year. In an ideal world any hole should really be welded up, but as Mat (and all world authorities concur) its not structural and - in the short term at least - stops the tin worm in its tracks - it also looks much nicer, which in my book - is good! If you want any help/advice getting it sorted drop me a PM. It's a fairly lengthy process making a good repair but we can't leave that lovely car of yours to the ravages of tin worm - that would be UNTHINKABLE!

[mat_fenwick]

I'd be interested to know how long your repair lasts Paul. Hopefully a good few years! The way I look at it (with the time I've got available without TOO much grief from Lana) I can either do a functional looking welded repair, or a neater one using filler so I'd chose the former. If I didn't have a welder I would fill it, and I have done so on other vehicles in the past, although perhaps not achieving *quite* such neat results!

[Paul296]

Well, I can't weld (I wish I could!) so I'm forced to take a rather pragmatic view; either I leave the car to the ravages of tin worm or take what steps I can to stop it getting any worse. Actually, when I made the repair, if I'd known Shaun as well as I know him now I may well have prevailed on his skills to weld a little plate in there, but I didn't so I made like Arfer Daley and - bish bash bodge! I couldn't just do nothing; in the few months I'd had the car it had gone from 'very crispy' to a hole and all things being equal - it's safe.

I did the repair about 6 or 7 months ago now and apart from some tiny bits of paint peel along the seam ridge its remained very solid. The only place it reappears noticeably is on the very end of the sill under the wheel arch; if I keep on top of that it doesn't seem to find its way any further forward.

Is it possible to weld a plate in then grind/sand it back before painting and finishing so that he repair is invisible?

[mat_fenwick]

Is it possible to weld a plate in then grind/sand it back before painting and finishing so that he repair is invisible?

Yeah, that's the ideal solution. You'd need to cut a patch to exact size, and butt weld it into position which is more difficult and time consuming than simply welding a patch on top. Hence most garages will do the latter, unless you request otherwise (and pay for it!)

There's a couple of photos from when I did the windscreen surround earlier this year here. I didn't use any filler on the patch after grinding, so it is still slightly visible if you look.

[Paul296]

There's a couple of photos from when I did the windscreen surround earlier this year here. I didn't use any filler on the patch after grinding, so it is still slightly visible if you look.

Yep, I saw that when you posted it and was duly impressed - I dread getting a rusty windscreen surround - I suspect that is structural?

[mat_fenwick]

It is structural, but haven't heard of a car failing the MOT for it even when holed (although is part of the defined load bearing areas in the tester's manual). The only reason I can see for it to start rusting, is if you have had a replacement screen fitted in the past and they've damaged the paint during removal. Otherwise the paint film under the seal should remain intact and not be a problem.

Sorry Jane - would you like this splitting off to a new topic?