Rustproofing double thickness sills

  1. badabec Forum Supporter

    Essex UK
    Hello, I am restoring a 1972 Citroen DS Safari, their name for the estate version. A normal DS has a box section sill made of 1.5mm steel. To take the extra load carried in an estate, the box section has an additional 2mm steel plate on the outside.
    In the 70s, no attention was made to rustproofing, so water wicked up between the two layers of spot welded steel, merrily rusting away.
    I've cut away the 2mm steel and the 1.5mm steel. A local firm has pressed up the steel. The sections are just odd legged 90 degree angle, 8 inches by 3 inches. I will cut to the correct shape.

    Question. What can I do to prevent water from wicking up between the sheets and rotting it again?
    The 2mm will be plug welded to the 1.5mm. Plus plenty of seam sealer.
    Zinc weld through primer? Hot zinc spray both new parts of the sill with localised grinding to help the welding?
    The parts labelled 13 (2mm thick) were originally spot welded to 11 (1.5mm thick). And he must have been paid by the spot weld, there are dozens, some almost on top of each other.

  2. bricol Member

    N.Yorks, UK
    Sounds about all you can do - as soon as you weld it, you will burn off the protection.

    Copious amounts of waxoyl type stuff?

    Any reason why you couldn't have used one layer of 3 or 4 thk steel ?
  3. mr haynes Member

    Shame you didn't get it made out of galv sheet
    Dcal likes this.
  4. anjum Member

    London UK
    Make them out of stainless!

    Or failing that

    weld together using whatever protection you favour, weld through primer, hot zinc spray (sounds good to me)
    and then epoxy prime, sikaflex, and epoxy prime again sealing the edges. (or you could solder/ lead fill)

    Then it depends on how the rest of it is welded together, I assume that 3 is the outer sill going down to the bottom. Is the double section welded to that? or does 3 connect to 8? Can you weld the bottom together first and slide the 13/11 section in? In which case you can spray epoxy primer (or your chosen solution) into the bottom seam

    I suspect the issue is largely due to a lack of sealing or using 50 year old mastic and a lack of drainage allowing water to sit in the sill and be wicked up. The rot pattern should give you clues as to where to concentrate your efforts.

    Then squirt in some way sealant until it runs out but doesn't block you orifices.

    Use sikaflex and epoxy primer and increase the drainage and it will last another 50 years!
    Dcal likes this.
  5. The_Yellow_Ardvark

    The_Yellow_Ardvark Member

    Is it possible to drill a hole, to be sealed with a rubber bung.
    The flood the cavity with a wax oil or similar?
    Pigeon_Droppings2 likes this.
  6. Burdekin

    Burdekin Chief Bodger

    Put some extra drain holes in. Spray with a rust converter and then Dinitrol ML.

    The rust converter works as a primer and rust inhibitor and unused stuff will drain out rather than clog up areas. Drill extra injection holes if needed and plug with grommets. Does anything else drain into your sills? If so drain holes in the sills near those areas will help clear water away.
  7. tom2207 Member

    uk northern ireland
    thats the way to go ,,, but I swear by ACF 50 ,,, i give a three year warranty on any part I repair , and on a land rover the only way I can do that is with ACF 50 . and for any one whos welded a landy you will understand how serious a three year warranty on anything is.
    Since the formula in Waxol changed about ten years ago , Ive seen it cause more problems than it solves ,,, it dries out now cracking and creates its own moisture holding cavities , water sits there , then the waxol floats a little at the edges and the water sits longer , but the big problem is it burns , so if you have to go back to repair something thats full of waxol you need a fire watcher ,, ACF does not burn , I always look at it this way , If Waxol was that great they would use it on aircraft , they dont ,, guess what they use ,, nuf said.
    vw1 and Dcal like this.
  8. Morrisman

    Morrisman Forum Supporter

    Can't you have them made out of a single thicker piece of steel?
    johnser and piman like this.
  9. steveo3002 Member

    cambridge uk
    id make some holes so it can be filled with a decent cavity wax , i think theyre pretty pretty reasonble on fresh metal

    never found the weld through primers to do alot , weve had cars back at work that have been crashed again and the seams were going rusty
  10. Dcal

    Dcal Forum Supporter

    Antrim Northern Ireland
    Hi @badabec brilliant motor and well worth putting the work into.

    My 2d worth
    If I was repairing that I would have used electro galv sheet. You will burn the galv off where you weld but the galv is self healing and whats left will slow down the corrosion.
    As you already have the parts folded in my opinion best options now are -
    1. - start again with galv sheet
    2. - Hot zinc spray, it's the next best thing to galv, period.
    3. - Zinc rich epoxy paint, the one I use is Jotun Barrier 90 but it's expensive. That's only because you need to buy a 10l pack. (It's cheaper and far superior to galvafrod per liter)
    4. - Single pack zinc rich primer like Galvafroid or Zinga.

    If you go for a paint option I would just paint the inside of the panels for now and paint the outside once it welded.
    All the paint options will need the steel blasted to work best, I'd say there is no point in using the Galvafroid type if you don't.
    Wear a mask when you are welding because all will boil off the zinc and it's not great to breathe.

    Then flood the cavity with the wax of your choice, I'd use Dinatrol ML but other (maybe better) options are available.
    Put it on as thin as you can and heat the panels to try and get it to wick in.

    A car like this has got to be worth it own thread.
    More details please.
  11. Pigeon_Droppings2 Member

    Zinctec sheet (or similar) as others have said.

    If you stick with what you have then I'd probably go with a very thin body wax....seal the panel edges....warm the panel and warm the wax so it flows when you put it in...

    Another option could be to use a very light oil....but I've never tried that myself.

    Personally I'd have the panel made in zinc coated'll be the best option and it's what I usually use for all my repairs.
  12. badabec Forum Supporter

    Essex UK
    This the DS. The other pictures show the extent of the rust. The jacking pin is just resting in place. The rubber pipes are a dummy build for the air con.
    I can't use a single thicker piece as the 1.5mm sheet slides behind the B post, the 2mm sheet butts up against it. I think the hot zinc spray will be my option. On a D, the part that the door shuts against is number 3. Attached under 3 are the fuel pipe and hydraulic return on the right hand side, hydraulic pipes on left hand side, they are protected from the elements by a decorative cover. The bottoms of the doors are exposed to all the crud, water and salt and nearly always rot out.
    You can see where I have cut through the 2mm plate and peeled it back. The rot extends the full length of the sill. The jack pin is only welded on the out side but goes through the entire sill. The jacking point is from another DS, mine is exactly the same.

    As an aside, none of the body panels are stressed. Rear wing one bolt, front wing three bolts, doors slacken off one hinge pin. So it used to be quite easy to tart up a rotting shell with decent panels and flog it as top quality. The saloon roof is GRP (metal on a Safari) and the bonnet aluminium, which has two bonnet catches.
    I'm replacing the front jacking point at present while I think about the sills. You don't need a jack to change a flat tyre. Put suspension on high, place the supplied prop under the sill, it locates on a pin, 15. Move the suspension to low, as the car sinks, the anti-roll bars trigger the wheels on the propped side to lift right up.






    jacking point2.jpg
    Springerdinger likes this.
  13. anjum Member

    London UK
    Fabulous car and project!

    Looking at the pic of the jacking point, I can now understand why it rots out from the bottom up.
    How, access wise, is 8 welded to 11/13???

    You need to seal the bottom edges of all 4 pieces.

    Whatever you do to seal the bottom seams of the sills sections, put some more drainage in on both sides of the partition formed by 11/13.
  14. badabec Forum Supporter

    Essex UK
    In this stylised sill cross section, the additional 2mm plate is spot welded to the left part of the box section. This extra plate also has a 90 degree return at the top, which is spot welded to the sill apron at the top. I've already removed the sill apron to gain access.
    The right hand black line is 8, the left hand 11, and 13, not shown, spot welds to 11 and the sill apron at the top.
    Maybe I should lie under the car and seam weld all three edges together.
  15. tom2207 Member

    uk northern ireland
    How I would go about the repair would depend on what I actually wanted as the end result , if the car is to go on to a concourse level restoration , then all the spot welds have to be replicated , no matter how much work is involved , money is not the issue , the end result is
    if the car is off to be a daily driver , or weekend car , then i would be happy to seam every thing then dress it back to tidy / nearly invisible , using the welded seam as seam sealer , drill 10mm holes paint the outside then ,rust proof , ACF 50 in my case making sure both cavities are done , then put sealing grommets in ... then it just needs a squirt every few years to keep work good ,, time consuming , but strong tidy and future proof.
    but thats just me.
    Dcal and Pigeon_Droppings2 like this.
  16. anjum Member

    London UK
    I'm not sure I see that your diagram matches the picture or the jacking point on the bottom left corner.
    But irrespective of that I think the key is going to be adding extra drainage holes at the bottom of both cavities with any seam sealing plan you choose.
    But whether you choose AC50 or wax type or epoxy primer, sikaflex followed by wax is your choice as I suspect no-one has experience of using these products 40 - 50 years ago but whatever you use is going to be better than the old technology mastics as in the jags or nothing as in your citroen.

    The designed in rust trap aspect (the jags are full of those) is something that doesn't change and you have the luxury of hindsight and can address those using the clues/ holes left by the current rust in your car and other examples of the same model.

    So given that your car has survived for all those years, even if you repaired it as was it would have a chance of surviving a similar period. With extra protection and redesign, who knows, it might even outlast the modern cars..:laughing::laughing:

    What I am saying in short is that you may be in danger of overthinking this....... Don't ask me how I know or how to stop doing it....
    stuvy and Dcal like this.
  17. badabec Forum Supporter

    Essex UK
    Yes, over thinking is my usual pastime. Or I get carried away and then have to cut it all off and start again.
    Concourse? No, definitely not. Rivet counters and those who call their car 'she' are two of my pet hates. Strong, tidy and future proof sums it up really.
    More pictures to follow. I'm still tidying it all in preparation. And one of my angle grinders, Bosch, has died.
  18. anjum Member

    London UK
    You named your angle grinder??? :scared: Sorry!!
    stuvy likes this.