Classic cars forum & vehicle restoration.

[UKdave2002]

I have read that early Minis had their sills filled with expanding foam, which reputidly really slowed down the corrosion process, I guess the lack of air limited the amount of condensation....

Couple of questions;

1) Did it work?
2) If it did why is / was it not more of a commen practice, and why did BMC stop doing it?

Cheers Dave

[Thief]

This was on the VERY early Minis as all the ones I have worked on had no foam.

I would think that it did slow the process down to a degree but when the rust did get hold, the foam would hold in the moisture and it would then be a rapid decent as the water couldn't drain or dry out.

Another more important factor is that the foam was a fire hazard and is probably the reason why they stopped using it.

[62rebel]

i can definitely reply that using household expanding foam is a BAD IDEA of dire consequence... the everyday stuff requires moisture from the air to cure, hence it retains moisture after curing and simply holds it against the metal. IF your internals are sealed or painted, this may not pose a problem, but the stuff also acts as a dam by holding liquid that would otherwise drain away. i might be tempted to use it in the roof or pillars; but never in the rocker boxes or boot voids. go back to good ol waxoyl and leave the foam in the house.

[buzzy bee]

Hi

That has given me an idea, someone should start making a water repllant expanding waxoyle sort of treatment, so it fills all of the gaps, and it coats everything in a nice coat of rust stopping/prevention! etc....

Cheers

Dave

[old gto]

Dave.... who-ever can come up with that formula will be a rich man! An "expadable" version of POR 15 ........HHMMMM!

[UKdave2002]

Took the Stag for an MOT this morning, was chatting to the guy who runs the garage about foam filled sills, he was an apprentice in the mid 60’s and they replaced loads of Mini non filled sills, then in the late 60’s early 70’s they got a spate of foam filled failed sills, in other words the foam filled ones lasted 2 or 3 times as long as the normal ones.

I have done a bit of research on the foam its self, whilst it does need moisture to speed the cure time up this is just normal atmospheric moisture, the foam its self can not hold moisture to anywhere near the level to promote rust, it wont absorb water either, which is why it is so popular in the building industry. It is the condensation that occurs within cavities that causes the us the biggest tinworm problems, the action of filling a cavity with foam, drives most of air out thus minimising condensation.

Here’s what I’m thinking of doing (but very open to suggestions !) with the Morris 8 sills which are not (MOT) structural but very prone to rust, probably because they have quite a big volume;

1. Drill 5 or 6 holes along the length of the of the sill including a drain hole.
2. To clean all the crap out I’ll power wash the box section through each of the holes
3. Thoroughly dry
4. To kill any surface rust ;spray in Dinitrol Converust RC800 (or similar, need to look at these product's in some more detail, any views?).
5. To protect the metal spray in a 2 pack primer (there are primers around now which claim to do the same as the above as well as prime? Any views?
6. As primers can absorb water I'll spray in a 2 pack gloss.
7. Good coat of warm Waxoyl will then be applied, I’ll warm the sill up with a hot air gun so that the Waxoyl gets in to all the nooks and crannies.
8. To drive out the remaining air; fill with foam
9. Seal the holes
10. Seal all seams


What are your thoughts?

Dave