The foam is sometimes sprayed into the cavity between the sills to stop rust from forming, the only issue with it is that if its not 100% dry then it holds moisture in, also the foam can sometimes harden to increase the stiffness of the chassis.

 

The foam is sometimes sprayed into the cavity between the sills to stop rust from forming, the only issue with it is that if its not 100% dry then it holds moisture in, also the foam can sometimes harden to increase the stiffness of the chassis.

So that time when I didnt clear the rear drain channels for 6 months and had a wet passenger side carpet could be really really bad news for the future now?

 

First time Ive heard of this, Only things Ive heard of people putting in sills is wax for protection, and newspaper when they are filling over a sill instead of welding it as a really nasty piece of bodging to fake the way through an mot...

 

And it's filling an air gap, so could be problems if it's always damp especially over winter. In Japan they have less worries with the old corrosion than we do.

 

You can get proper water proof foam for this purpose, it is done to stiffen the car up. It was probably done in Japan like you say by the same person that fit the cage.

 

^ I'd go with that, it's probably been added in Japan as an attempt to stiffen it up.

 

Thanks guys.

Sounds about right for what else was done to the car, it had both front braces from japan and a serious structural harness bar \ cabin brace on top of the cage that was fitted with sandwich plates properly etc. The also had a fujitsubo manifold and HKS induction kit as well, so I can see that stiffening foam would be right down the same alley.

Will have to pay extra attention to keeping drains working etc.

 

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Doesnt matter if the foam is water proof, itll still allow a bit of moisture to be help against the metal which will rot. Overall a bad idea IMO, I have seen a number of the US guys recommend it to improve chassis stiffness as well but there are better options focused around bracing.

 

If you put a Mig welding torch within an inch of that stuff the car will go up like a Roman candle I should imagine.

Foam filling is a terrible idea, seam welding is what they should have done for added stiffness, like they do to rally cars.

 

If you put a Mig welding torch within an inch of that stuff the car will go up like a Roman candle I should imagine.

Foam filling is a terrible idea, seam welding is what they should have done for added stiffness, like they do to rally cars.

Didnt think to test the excess stuff I had to remove to fit the sill protectors for fire safety might have find some and test it. I know you CAN get stuff with a good fire rating, but I also know the cheap stuff for house use burns very nicely indeed. No way of telling which it is without testing it I guess.

I suspect that this stuff was massively cheaper than a thorough seam welding job by a massive amount What can someone charge for some foam to fill the sills with? £30 maybe £50? I guess maybe a professional may be charging £150 tops for that sort of bodge. Professional seam welding of a car could easily cost well north of £1000 up to maybe £2000, although fortunately not so much stripping required in mx5.

Neither my idea or choice, only just discovered it after 2 years of ownership, but to be fair shes a 23 year old car that hasnt had the sills welded yet and drives fantastic, Its not the way I would go about things, but its not made the cars lifespan terribly short either. But must look at the fire safety side...

 

I doubt it will catch fire any quicker than your shirt and jeans would mate. Don't worry about it.