Expanding foam - advice please

[DavidofMersea]

I recently bought a wooden Enterprise with inflatable buoyancy bags. It is difficult to varnish inside the bow, and I wondered about standing the Enterprise on its bow and filling the space under the foredeck with expanding builders foam. Not only would this save a difficult varnishing job, but provide extra buoyancy - Is this a good idea?

 

[boatbuilder]

It is the worst idea in the world, the foam retains moisture and would resort in rotten ply in a very short time.

 

[fisherman]

Some foam is not 'closed cell', and absorbs water.
In any case I think the wood will rot behind it. FWIW. IMO. TIoLI.

 

[Topcat47]

Basically no. The foam is not closed cell and once any damp gets in, it'll soak it up and eventually turn to mush.

 

[Thistle]

It's not generally a problem with Enterprises. All the ply should have been treated with epoxy before the bow compartment was built so, unless there has been damage, it shouldn't be prone to water damage if some simple precautions are followed. I assume you have a drain hole right at the lowest point of the bulkhead and you should also have an inspection hatch further up the bulkhead. When the boat's ashore, ensure that she's left bow up with both the drain hole and the hatch open. This will allow any water to drain out and give plenty ventilation to encourage drying.

If you feel you must varnish inside the front tank, think about using well thinned varnish in a sprayer. One of the pump-up ones intended for garden weedkillers etc with a long nozzle is quite effective.

 

[VicS]

Builders foam is not closed cell so can absorb water. Two component foam is closed cell and is often used for buoyancy in canoes.

 

[DavidofMersea]

The can says ".....giving a long lasting damp resistant seal". Are you sure you right?

 

[Topcat47]

Yes, it can dry out if there's engough airflow around it, but not if it's permanantly soaked and it will get soaked in the place you're trying to use it.

The key word is "resistent" not waterproof.

 

[vyv_cox]

<< Two component foam is closed cell and is often used for buoyancy in canoes. >>

where it also absorbs water over time. I have built many canoes, and before finding out that the foam treatment doesn't work, I have also dug out lots of two-component expanding foam from them. It becomes totally waterlogged over a period of time and adds pounds to the weight of the canoe.

 

[billcowan]

What happens to an 'unsinkable' Etap yacht then?

OK the foam is sealed in, but what about when it gets old.

 

[vyv_cox]

Completely different animal. My Sadler is the same. LNG tanks are sprayed with the same stuff. Industrially applied, closed cell foam under strictly controlled conditions. Totally different from two beakers of liquid, stirred up with an electric drill or maybe a spatula and poured into a hull that might be wet, waxy, full of debris, who knows, at any temperature between -10 and +40 C. No pressure applied to ensure cell size within limits.

 

[mikejames]

The varnish inside the bow will not need as much care as the sun doesnt shine on it. If you want a heavy bow down dinghy go for the foam. I once had the misfortune to sail in a Firefly that had been foam treated by the owner of a building insulation firm (in the best chuck it all over tradition) and he had made a soggy slow lump out of a nice little dinghy.

 

[Doolittle]

[ QUOTE ]
What happens to an 'unsinkable' Etap yacht then?

OK the foam is sealed in, but what about when it gets old.

[/ QUOTE ]

The same as a waterlogged pre '70's Dell Quay Dory: Drill many holes in the transom, using a stick push holes through the foam as far as possible then turn it on its end for a few months. With any luck it may float a few millimetres higher in the water!

 

[richardandtracy]

There is a world of difference between a builder's 'Damp Resistant' and a boat owners 'Won't waterlog if permanently subject to getting wet in a high RH environment'.

Over the long term moisture vapour will diffuse through any organic material. If there are voids in the material then the vapour can condense out and it will form a liquid. This is no problem in the low RH environment inland, because in hot weather the process will work in reverse and the foam will dry out enough for it never to waterlog. Near the water though, where the RH rarely falls below 80%, the RH will not drop enough for the process to work backwards fast enough and the foam will inevitably fill with water. The only thing you can control is the speed of filling, by reducing the surface area through which moisture can enter - by encapsulation in a low permeability membrane (or preferably grp laid up with aluminium foil).

This process does happen with aeroplanes and their honeycomb panels. I have seen perfectly intact Nomex cored aeilerons on a commercial airliner where the cells were 50% filled with water. No cracks or anything in the adhesive. It was simply due to diffusion of moisture through 0.02" thick glass/epoxy skins on the surface. The weight was 5x what it should have been...

Regards

Richard.