Expanding foam - waterproof?

[DRFT - 86]

Does anyone know if this stuff is waterproof......or does water soak into it at all?

reason I ask is... where my loom goes through the firewall..the rubber gromett is fucked.....(I have one to replace it but that means I would have to mess around heaps just to get the loom through it as there is no way of disconnecting one end exactly) so...I was thinkin of filling the cavity around the loom with expanding foam to stop water entering.

dont want to use it if it holds water....as this will no doubt lead to rust....

or does anyone have a better idea than this....?

cheers

[ae86levint]

silicone, don't try and paint it tho. expanding foam is full of air bubbles not sure if it will hold water tho.

[DRFT - 86]

yeh it has been siliconed b4, but it hasnt worked that well.......hmm I am pretty sus on foam been waterproof though ahy......it might have to be silicon again......

also how can you tell if a silicon is non-acid bearing..... (I have a tube at the moment but it dosnt say anything about this)

[RobertoX]

ask funk doc, his whole car is foam

[NickAE86]

in my experience not really. The foam itself is but its the seal between the foam and the surface you're applying it to isnt. I've had to use the stuff at work when mastik hasnt been available and in certain areas where water (constantly) is present some very slow leakage has occured but for what you want to use it for it'll be fine

make sure you clamp/cover the area after you've filled it to contain the foam and stop it from going everywhere

if you can get your hands on some mastik its good stuff...its black, sets like rubber and is fire rated

[Medwin_3sGTE_AE86]

Completely water proof... the stuff once set is like hard plastic... i gots to show you's a sample one day... u'll know what i mean....even tested with a blow torch... flame proof too.... DOES NOT BURN!!! after about 30 sec of blasting with a torch... the stuff just sizzles away (slowly) producing a black smoke....but does not burn...

Comes in different densities too... with different expansion rates...

i have to admit i went a lil overboad... but i'd definately put it in all the cavities in the cross members and chassis rail.... The chassis is now like ROCK!! i've heard of chassis torsional stiffness increases in the order of 1-300% !!!!!

Although this sounds crazy...but its not that hard to beleive when u really think about it... thats what they are using to build boats these days... Sandwich fibreglass with foam inside... this shit is STRONG!!! and 1/3 of the weight of fibre glass of the same stiffness... What i've got now is Steel/foam sandwich...

I cant be bothered to explain why atm...but i might post up the "science" behind this if yous what... its got to do with transferr of energy from bending to compression...

[samuel]

Thats a pretty interesting idea you have there, I would be interested to know how much it has increased your total weight now, but still - well worth it in the long run if it does what you say.

[Medwin_3sGTE_AE86]

i highly doubt u can use expanding foam in ur situation... u'll need to make a mold for that area to contain the expanding foam... plus... the foam is strong in compression... not for much else... if theres heaps of movement i reckon the foam will eventually crack up...

[RobertoX]

whose hungry for a foam sandwich?

it is something that requires a LOT of research as it can be easily stuffed up!

[Medwin_3sGTE_AE86]

One set chemicals came in 2 parts... 5 kgs each... i used about 2 sets... that would be 20kgs i guess... if i only used it in the areas i said b4... one set would be more than enough...
The chemicals are exothermic... and do not require oxygen or any other gases in the atmosphere to activate.... there fore the end product should weigh less than the original 2 ingredients.... by how much.... no idea....