Morris Minor Owners Club

Hi, has anyone tried filling the box sections with expanding foam to keep the damp out?

Chris

Hi

Not a good plan - it will soak up salty water at the first opportunity and rust out double quick!!

I don't see a huge problem as long as you waxoil them first. Many modern cars have box sections filled with foam to reduce noise. Just remember to dig it all out if you have to weld in the area as I imagine it is highly flammable...

not a good idea imho

oldmod1968 wrote:Hi, has anyone tried filling the box sections with expanding foam to keep the damp out?

Chris

NOOOO ! Don't do this unless you want to trap water and rot out your chassis legs!

Just spray the inside of the legs with a wax rustproofer such as Dynax or Dinitrol 3125.

Once had a boat with a foam filled hull. Thought it was very heavy when on tow so had it weighed at a weighbridge. Turned out the hull was full of water, held in by the foam!!!

I once had to weld a Ford Escort up that had had the Sills filled up with Expanding Foam it was all we could do in the Workshop to stop the car going up in flames (2 fire extingushers later and i dug out what i could before i MIG welded it). Also it obviously didnt stop the rot if anything i often wonder if it accelarated it, as the rest of the car was in quite good order.
As for modern cars having foam put in their box sections, most modern cars never need welding and are consigned to the Scrapyard on engine or electrical faults (modern cars are becoming to complicated and expensive for parts) so unless they are accident damaged the subject of welding never arises, also i doubt they actually use expanding foam as we know it. My advice is i wouldn't bother better to use Waxoil (mind that burns well too) and keep the airflow within the box sections then if water does enter it can at least dry out over time. Ade p.s. If youv'e already done it i'm not welding it in the future!!

Hello all,

as the foam is waterproof and non absorbent I don't see how it can "soak up water". The other thing it should do is prevent condensation, a bonus in my view?

Alec

i would advise waxoil, brilliant stuff, just dont get it in ur hair like i did

Water would find it's way in between the foam and the metal and stay there with no air flow to dry it out.
Bad plan.

The very first Minis had foam filled sills. My 'race' car was an early shell - and after an attack from another car - I had to repair the sill area - and after the foam had burned away ( ) the metal was still in excellent condition inside the sill - better than most of the shell! But seriously - for your Minor - just waxoyl it!

MarkyB wrote:Water would find it's way in between the foam and the metal and stay there with no air flow to dry it out.
Bad plan.

Exactly!!

Expanding foam is designed for building use and not automotive use. A car is subject to vibration, movement and flexing of the panels. The foam would loose its grip on the chassis leg (assuming it had filled it completely!- voids will also trap water) and the gaps between foam and metal would be the perfect water and rust trap. Besides which, these foams soak up moisture like a sponge- and keep it there. See the above post on the foam filled boat.

Very bad idea, by the way I may have traced the original source of this DIY bodge. Page 31 of "Pittmans all in one book of the Morris Minor 1000" published by Statton Abbey on page 31 it suggests this bodge as an alternative to bridging a rusty hole with zinc mesh and fibreglass:-

"When repairing a hollow section, a self foaming plastic can be poured into the cavity until it overflows from the hole, quickly setting into a sufficiently rigid mass to provide good support for the glass fibre sheet".

So if you are into bodging your B pillar and doors with fibreglass then by all means pour expanding foam into every box section!

Hello John,

expanding foam is a very general term, there are many types and is used for industrial applications as well as building. It sticks very well to metal, and is non absorbent. We sprayed (I forget the type now) the base and top of our brewing kettle, which is stainless steel nearly four years ago and it is still there. This gets sprayed with water and has temperature variations between 20 degrees or so to boiling.

Alec

as the foam is waterproof and non absorbent

The normal expanding foam that you buy in a can for building work creates an open cell foam therefore it is absobent and i.e. NOT waterproof. also it burns readily...

The stuff used for noise insulation is higher density closed cell foam. Modern vehicle box sections are NOT foam filled due to weight, cost and it's not needed anyway! The type of wax/oil protection they now use is extremely good.

Alec wrote:Hello John,

expanding foam is a very general term, there are many types and is used for industrial applications as well as building. It sticks very well to metal, and is non absorbent. We sprayed (I forget the type now) the base and top of our brewing kettle, which is stainless steel nearly four years ago and it is still there. This gets sprayed with water and has temperature variations between 20 degrees or so to boiling.

Alec

That doesn't mean it is suitable or even sensible to use on a car, where the foam will be subject to vibration, movement and flexing over a longer period of time that you have had it on your kettle. The temperature change of 80C has nothing to do with it a car never sees boilling temperatures!. Besides which, the expanding foam accessible to most folk will be the open cell building type, which DOES soak up water, and any foam will lose its adhesion over time and use of the vehicle, thus trapping water and making the rust WORSE than it would have been.

Really, as Ray said there is no point in filling your chassis with foam, cavity wax is the best solution to protecting box sections.

I think on the Morris Minor site we should be responsibly encouraging people to use the best practice methods for restoring and preserving their Morris Minors, not perpetuating decades old bodges!

Hello John,

the temperature change was used to illustrate an adhesion with movement as the steel is expanding and contracting.

Certainly an open cell foam is not suitable, but I was trying to balance the rather dismissive earlier replies. Everything needs to be done correctly for a lasting result and this is no different and it has certain merits. It is not something I have used nor intend to but I think some pro views should be aired.

Alec

I recently heard a story of a local Minor owner who had treated his car comphrenesively with Dinitrol. Unbeknown a prev owner had done the expanding foam trick with the sills and B posts. A small bit of welding then needed to be done which resulted in a blazing B post,which wrote off the door trim, rear 1/4 trim, wood capping (traveller) and the roof lining. Quick action with the fire extinguisher saved the car. The insurance was void due to the 'non standard modification' being a fire hazard.
I'm really glad it didn't come to me for the welding job...

Hello Iain,

that is one of the hazards of foam filling or, equally, using a wax based treatment. Sills in particular can be hazardous as often the welder is out side or underneath and may not see the flames. Not such a big problem if the car is stripped but if the trim is still in place makes this a real risk.

Alec

You can easily remove wax treatment from the areas to be welded with a rag soaked in panel wipe (then obviously leave the panel wipe to evaporate), cannot do that if the chassis is filled with foam. Another reason not to fill your box sections with foam- and yet no good reason for doing so!

Hello John,

that's all well and good if you can access the area, very often it is totally inaccessible.

Alec