Expanding foam

I was thinking the same thing a while back but was warned off, I am sure it was a pretty good reason because I am incredibly stubborn and would have done it, but for the life of me I can't remember the reason!

I think it would have caused worsening of the corrosion but can't be sure, I think that someone has done tests on some mild steel tube, possibly strand plastics (Glass fibre and foams etc)

I normally waxoyl the sills and make sure there are lots of drain holes if they are the oversill variety!

It seems some of the later minis suffered a little from quite bad rust, shame they had to skimp on quality of steel!

miniman

Hi, "oversills" are pure bodges. Apart from the rusty original sills rusting the "oversills" at a very fast rate, the sills are considerably weakened by fitting these things. The reason is that they completely change the cross section of the sill beam. The sill is no longer a box section.

depends how you fit them, I wouldn't leave the old ones in and they make for a stronger joint if you seam weld all round and then spot weld or plug weld where the originals went (assuming the floorpan is in good enough condition to take it. The other thing to remember is that these 'things' are usually made from a decent gauge steel in comparison to a lot of pattern parts.

I fitted original sills, chopped out any corrosion, blasted with waxoil, so foam filling sounds ok, ???? what do you think ?? Fitzy

This was done at the factory around 1961- 1962, the problem was if welding work had to be carried out later (i.e. accident repairs) the fumes from the burning foam were poisonous.

If any water gets in you could have problems, it may find its way down the door pillars & you will end up with water lodged in places, if the waxoil is in the sills you should be ok.

Steve.

The main reason they used filling foam at the factory back then was to combat the water leak problem on early Mini's. Once they started to weld the floorpans correctly they stopped using foam. But it is said that the sills on these Mini's were still in good shape years later when they were cut up! But waxoyl or dinitrol is the best product to use on Mini's now.

Taffy

Thanks people, I have waxoiled the sills, I will inject them with foam at the weekend, I will let you know how they are in about 8 or 10 years time ;-) Fitzy

I would avoid expanding foam like the plague. There is very good reason virtually no manufacturer uses it. Basically it will hold the water in pockets inside it, if these pockets are next to metal it will hold the water next to the sill and rot it quite quickly. Just like mud under wheel arches that isn't cleaned off holds the water next to meatl and can lead to rotten arches. The foam will also deteriorate when trapped water freezes and expands etc leading it to break down, when this happens it might block the drain holes you are relying on to keep the sills clear!

Waxoyl is the way to go, not sure if ziebart is still around? A friend of mine used to swear by putting about 250cc of used engine oil in thru a small hole, then cleaning off what eventually came out of the drain holes before driving!

Chris

If the expanding foam does hold water how much extra weight could you be carrying around?

I feel an experiment coming on here chaps, a metal container ......... possibly a food container, tin can, open at both ends, wax oiled inside and out, then filled with expanding foam, then left in the garden, what will the outcome be ,,,I wonder, Fitzy

One possibility I guess is that two slugs will meet, fall in love, get married, move in... and have lots of baby slugs.

Any other ideas?

It is likely to trap inside the moisture. Yes, moisture will find its way in, whatever you do. It's better to give moisture a way to evaporate or drip away than to trap it inside.

Plus, when the day comes that your sills need some welding, that foam can produce some VERY NASTY fumes. Nasty as in deadly.

I had a 1960 mini that didn't have foam in the sills & they were rotten. I also had a 1961 mini that did have the foam in the sills & they were still in good condition 45 years later. I don't know how the original foam compares to modern crazy foam but it seems to have done some good.

Foam sticks to the metal and is closed cell - so if you place enough in the holes then moisture can't get in. Its used as floatation in boats.

Anyway as I said before your far better using Waxoyl or Dinitrol. Okay Waxoyl is cheaper and more popular, but it can be a pain getting it to flow right as you need to thin it down and warm it up etc, but from what I've heard of Dinitrol, it's more expensive, but it has a better creep? consistency, but if you can get Waxoyl set up right that's just as effective too.

Taffy

Yep no way for me to try filling with foam either.