Help please - expanding foam

[DavidofMersea]

I have some useless voids in my boat that it would be good to fill for buoyancy in case of leaks or being holed.

I am proposing to use Polyfilla Expanding foam, but my neighbour says that this is Hydrostatic (soaks up water). There is nothing on the tin about this, has anybody else had experience of using Polycell expanding foam?

 

[Malcb]

Yes it will soak up water, in fact most of the foams will eventually from what I've been told by people who know more than I do.

 

[snowleopard]

Polycell expanding foam is better than most, in fact it is used for waterproofing in the building trade. The one to avoid in any application that could get water in, i.e. below waterline, is REP (rigid expanded polyurethane) which is the one formed by mixing two liquids.

For just using up space that could get filled with water, expanded polystyrene is as good as any. You can't expand it in place but you can stuff blocks or sheets into any cavities. It lasts very well and is often used for pontoon floats which are constanly immersed.

The best of all is PVC foam, e.g. Airex, but that costs a fortune.

p.s. I think the term you were after was 'hygroscopic'.

 

[Anchorite]

Foaming at the mouth

Hydroscopic /forums/images/graemlins/laugh.gif

 

[DavidofMersea]

Thanks for that Snowleopard.

You are saying "you can't expand it in place", but the stuff that I have is in an airosol (that not spell correctly, but I am sure you know what I mean) can.

I think I meant hygroscopic, but I meant stuff that soaks up water

 

[smiala]

hi,
we have an Etap, with foam all over the place!!!, but not much locker room /forums/images/graemlins/frown.gif
you shall need plenty if you dont want to sink....

Beware if yuo do use expanding foam then it does what it says on the can, been there done it.
If you use too much in a tight space then it can warp the hull, use in moderation and repeat.

 

[Channel Ribs]

We have been toying with epoxy resin and polystyrene balls, the latter being very cheap and buoyant, any thoughts on the usefulness?

 

[smiala]

the epoxy would add strength to the area concerned i guess but would'nt the mix out weight the benefit of the beads, not sure if epoxy floats. You'll not get it in the upper voids as easy as drilling holes (inside of course ) here and there for the foam tube.

Just buy an etap. /forums/images/graemlins/wink.gif they,re great fun.

 

[Colin_S]

Hi David. Finally got the cat I see.

From experience with other watercraft (jetskis) that use a form of expanding foam for bouyancy they inject the foam into strong sealed polythene bag type containers to keep out moisture. These 'grow' to fill and assume the shape of the void where they have been placed prior to filling.

Hope that makes sense.

 

[duncan]

beware the introductionof rigid areas where the hull flexes

 

[Topcat47]

I too have voids that would be best filled with some closed cell foam. DO NOT use building foam as it IS hydroscopic.

Filling with epoxy and microspheres has been ruled out for me as the reaction between the resin and hardener is exothermic. Mixing and pouring enough to fill the voids will overheat the hull. Doing it a little at a time to avoid this will take forever. West Systems gave me that advice.

Even using rigid foam will only work until water gets in. Next time you haul out over winter, the water will freeze and crush the foam.....many times...destroying the integrity of the foam and letting more water in when you go afloat next season etc....

If anyone knows the remedy for this, I'm all ears.....

 

[lancsjohn]

beware fibre glass resins will melt expanded polystyrene but some expanding foams will mix happily with ploystyrene pieces. using foam in a plastic bag will fill space and will not stick to surface so needs to be trapped in position or will float away.Try foam mixed with some scrap polystyrene packing that should be cheap and will reduce any water take up. Remember one cubic metre of polystyrene will give approx 1000kg buoyancy.

 

[cliff]

[ QUOTE ]
I too have voids that would be best filled with some closed cell foam. DO NOT use building foam as it IS hydroscopic. <snipped>
If anyone knows the remedy for this, I'm all ears.....

[/ QUOTE ] Here is one solution /forums/images/graemlins/grin.gif

and here is another /forums/images/graemlins/smirk.gif

And would you believe it, yet another one /forums/images/graemlins/wink.gif

--------------------

"Artificial intelligence is no match for natural stupidity"
sailroom <span style="color:red">The place to auction your previously loved boatie bits</span>

 

[thefatlady]

Re: Foaming at the mouth

Hygroscopic.

snowleopard is right.

As far as I can ascertain, "hydroscopic" does not exist as a word.

Strictly speaking, "hygroscopic" refers only to absorption of atmospheric moisture.

 

[halcyon]

Re: Foaming at the mouth

Is not absorption of atmospheric moisture form part of the chemical reaction, foams better in a damp area, than in a dry one ?

Brian

 

[Channel Ribs]

[ QUOTE ]
Here is one solution /forums/images/graemlins/grin.gif

and here is another /forums/images/graemlins/smirk.gif

And would you believe it, yet another one /forums/images/graemlins/wink.gif



[/ QUOTE ]

Superb, I have gone for option 2! /forums/images/graemlins/smile.gif

 

[thefatlady]

Re: Foaming at the mouth

Might well be, often is, but that's not relevant to the meaning of "hygroscopic", the existence of "hydroscopic" or whether the final product is hygroscopic.

 

[snowleopard]

When I mentioned polystyrene foam, I'm talking about the white stuff you get as packing in e.g. TV boxes. You can buy it as granules which expand in hot water but that's no use for your application. Polycell expanding foam is something quite different.

As for moisture absorbancy, the manufacturers only say 'for insulation against heat, sound & moisture. In the building trade they tend not to worry about things like seawater! This question comes up pretty frequently so I've started a little experiment - several types of foam in a jar of water. I'll report back later (quite a lot later).

 

[Signed Out]

It was suggested to me to use (insulation in my steel hull) standard polystyrene, and just squirt some of the expanding in around it to seal it in place.

 

[Wansworth]

Doubtful idea .You will get condensation in the air sapce behind the loose poltstyrene and womnt be able to inspect it.Insulation should be directly stuck to the steel or be removeable,imho.