20 replies to this topic

[toadstool]

Hi
Ive been out of the mini game for a while but i seem to remember one of my mates filling his sills with expanding foam to stop the water getting in, has anyone tried this?

[sonikk4]

Don't do it, it will trap water. You are better to inject Waxoyl.

[garrett3]

A bodge sounding idea,

As above, waxoyl is king

[pdaykin]

Something similar was done by the factory on very early cars. Not sure what kind of foam it was - probably banned now !!!

I understand that it was quite effective at stopping rust but it couldn't eliminate it.

IIRC it was discontinued due to the health and safety implications when it came to do sill replacements/body repairs.

[tiger99]

I don't think they actually discontinued it because of the health risk, just the cost, once the water leak, which was not actually the sill, had been fixed, but the health risk during welding was very real. Actually, it was the same health risk as two pack paints (isocyanates) plus some fire risk, because it was polyurethane foam. I read somewhere that BL bought back some of the early foam filled cars in the late 1960s to investigate, and found negligible corrosion.

Personally, I think foam filling is a good idea, if you use the correct foam, accept that you can't do welding without removing the foam first, and put it into sills with no existing rust. But they would ideally need to be configured inside out, i.e. the floorpan extends up to the side seams, and the sill is on the inside. There might be assembly difficulties, like having to put the seat crossmember in last, if you modified a later Mini like that.

I have just acquired a second-hand copy of Pomeroy's book, which I thought was the one which told the sill story properly. It isn't, and he thought the leak was at the sill, but I know that one of the books written in the 1960s did tell the story in some detail, including the improvement in torsional stiffness. Filling the A pilars would also be useful.

You can still get suitable foams, which need to be closed cell and highly adhesive. Google will find them.

[Tupers]

Sounds like a good way of destroying your Mini in a few years time.

It worked on early Minis (59-60) as the sills were constructed differently to latter Minis and had no external vents or seams. With latter vented sill you will get water up in them and most of the time will will run out again providing it's got a good coating of waxoil inside. If you fill them with foam it will retain the water and cause accelerated corrosion and be an absolute nightmare when it comes to repairing it.

[tiger99]

Closed cell foam, which forms a bond to the metal, does not retain water, either within itself or against the metal surface. It is not like a sponge. But as you say, it will not work on the later sills with the vents. You need a sealed cavity to inject it, so it remains under pressure.

[TopCatCustom]

They used to foam fill cavities in rally cars because it made them a lot stiffer and stronger, thats about all I know though!

[JustSteve]

so, what about foam-filling over-sills?

Two bad ideas could make one good idea?

[jakejakejake1]

so, what about foam-filling over-sills?

Two bad ideas could make one good idea?

Well oversills couldn't get much worse haha

[Ethel]

Surely it has to be closed cell or it wouldn't be possible for it to expand & be injected? Beetles are full of the stuff and it's never been mentioned as an issue.

[Bungle]

are they, where ?

[tiger99]

Ethel, I follow your reasoning. Open bubbles would let the gas out, so would not expand. Makes perfect sense.

Non closed-cell foams do exist, and I suspect that the cell boundaries only break down as the stuff is setting. I suppose there must be experts in that field somewhere who would know. Don't know what they would be called. Foam chemist? Foam engineer?

I would very much like to find such a person for advice before I get my next Mini, or at least before I start the inevitable welding.

[tiger99]

JustSteve,

Don't get me going on oversills! An abomination which should not be sold as a Mini repair panel. More like a death sentence for the poor little car.

And there is the dangerous bodger's inner sill, which goes with them, with a nice big cut-out to fit over the seat crossmember, losing 80% of the strength and 90% or the stiffness....

[Ethel]

Bungle, I remember having to chisel my way through Dubba 3/4 panels to liberate their looms for beach buggies because of the stuff - 1970's models, I don't know how many were like that but all I saw were.