how thick should spray foam be?

[Chris Pink]

..

Edited April 28, 2012 by Chris Pink

[Steve Goddard]

Stuart

 

Details when I had Siskin sprayed Siskin. The effectiveness of the foam will depend on both the thickness and the quality fo the foam but your minimum should be no less than 25mm. The thickness you have will really depend on the size of your battens. In Siskin they are 35mm set about 5mm off the steel sides so i'm at about 35mm and working inside Siskin over this winter has shown that even with very little heating it's ok.

If you look later on in the blog you can also see how I've run the cabling.

 

 

Steve

[designerstuart]

I have a minimum 2" all over accept the base plate.

 

My spray foamers said 1" is 87% efficient, 2" is 95%. I have no proof of this statement. But it seems to work pretty well.

 

Linky

thanks for your link, useful

 

Stuart

 

Details when I had Siskin sprayed Siskin. The effectiveness of the foam will depend on both the thickness and the quality fo the foam but your minimum should be no less than 25mm. The thickness you have will really depend on the size of your battens. In Siskin they are 35mm set about 5mm off the steel sides so i'm at about 35mm and working inside Siskin over this winter has shown that even with very little heating it's ok.

If you look later on in the blog you can also see how I've run the cabling.

yes thanks steve, yours is one of the blogs i have read through in an attempt to cram knowledge!

 

we had a company sorted, but now can't get hold of them. any recommendations out there please? we're in newbury, berkshire if it matters.

 

thanks all

 

ps. both 'gunnel' and 'gunwale' seem to be correct but i expect there is a more long-winded answer out there!

[designerstuart]

I have a minimum 2" all over accept the base plate.

 

My spray foamers said 1" is 87% efficient, 2" is 95%. I have no proof of this statement. But it seems to work pretty well.

 

Linky

 

By the way Biggles, i had your guys in to do the work. Excellent. very nice chaps and best price too. Nearly drank me out of tea though!

 

Would certainly recommend CosyHome to anyone looking for a good job.

Edited July 23, 2012 by designerstuart

[nb Innisfree]

After we had our shell spray foamed by an established firm I carefully inspected and found quite a few hard to reach places where the foam hadn't quite penetrated fully, unavoidable really as the spray is directional. I finished the job by injecting aerosol foam into tiny cavities, took nearly a fortnight of re-inspecting to finish but even then a year or so later I found one tiny spot behind the bathroom lining that dripped slightly in very cold weather, A quick squirt with the aerosol sorted it.

 

I suspect some minor drips are very common on boats, usually concealed behind lining.

 

ETA: You can get condensation on foam, in very cold weather we had it forming on 1.5" of foam on the underside of the front deck, caused by cold air trapped in the well deck maybe? Fitting a cratch cover cured it (by reducing the temperature differential I guess)

Edited July 23, 2012 by nb Innisfree

[Ex- Member]

After we had our shell spray foamed by an established firm I carefully inspected and found quite a few hard to reach places where the foam hadn't quite penetrated fully, unavoidable really as the spray is directional. I finished the job by injecting aerosol foam into tiny cavities, took nearly a fortnight of re-inspecting to finish but even then a year or so later I found one tiny spot behind the bathroom lining that dripped slightly in very cold weather, A quick squirt with the aerosol sorted it.

 

I suspect some minor drips are very common on boats, usually concealed behind lining.

 

ETA: You can get condensation on foam, in very cold weather we had it forming on 1.5" of foam on the underside of the front deck, caused by cold air trapped in the well deck maybe? Fitting a cratch cover cured it (by reducing the temperature differential I guess)

 

Another useful tip from the welder who built the boat, is to use aerosol spray foam to fill tubed ribbing as there can quite often be water trapped inside, drill holes every metre in ribbing and inject, wait a few mins until it exudes from the next hole. I was surprised that when drilling the ribs at the edges of the roof internally to see drips of rusty brown water exuding from drilled holes. I then blew air through ribbing and quite a lot of rusty water came out in quite a few places.

Edited July 23, 2012 by Julynian

[wandering snail]

When the spray foam insulation was taken off our damaged bedroom wall this week we were surprised to see the coating of rust under the gunwales. The boatyard reckon 2" is insufficient hence the rust.

[designerstuart]

When the spray foam insulation was taken off our damaged bedroom wall this week we were surprised to see the coating of rust under the gunwales. The boatyard reckon 2" is insufficient hence the rust.

in one sense i don't really understand this - don't most boats have less than 2" or 50mm insulation? and as they often use polystyrene or rockwool, which have lower insulation properties, would this not mean that all boats are insufficiently insulated?

 

but then, i do understand this, seeing that houses built today by law must have something in the region of 270mm roof insulation - and they aren't built from steel!

[nb Innisfree]

When the spray foam insulation was taken off our damaged bedroom wall this week we were surprised to see the coating of rust under the gunwales. The boatyard reckon 2" is insufficient hence the rust.

 

Yes the thicker the better under gunwales, not to prevent rust but to prevent condensation forming on the underside of the foam

 

For rust to form oxygen has to be present, spray foam excludes oxygen so even a thin coat that has adhered correctly to the metal will prevent rust. So either your foam didn't adhere correctly in the first place and allowed air to come into contact with the steel and resulted in rust forming or rust had already formed beforehand. Before any foam is applied any loose rust or paint should be removed, ideally a coat of good quality metal primer should be applied to improve foam adherance.

[wandering snail]

Yes the thicker the better under gunwales, not to prevent rust but to prevent condensation forming on the underside of the foam

 

For rust to form oxygen has to be present, spray foam excludes oxygen so even a thin coat that has adhered correctly to the metal will prevent rust. So either your foam didn't adhere correctly in the first place and allowed air to come into contact with the steel and resulted in rust forming or rust had already formed beforehand. Before any foam is applied any loose rust or paint should be removed, ideally a coat of good quality metal primer should be applied to improve foam adherance.

Yes, we are very puzzled about this as the walls were red oxided by the boat builder first and the foam applied by a well known company. Making us wonder what's happening underneath the rest of it

[Ex- Member]

Yes, we are very puzzled about this as the walls were red oxided by the boat builder first and the foam applied by a well known company. Making us wonder what's happening underneath the rest of it

 

It could be areas that were dusty and the foam simply didn't take.

 

 

 

[designerstuart]

we had a bit where wax oil had been applied and the spray foam did not stick to it at all. luckily only a small patch we'd missed when we were cleaning it all off.

[Tam & Di]

Below the gunwhales is more important in my opinion. Although heat rises, it's below the waterline where you generally get the most heat transfer.

 

 

Except that foam spray also keeps a boat cooler in the summer too - Friesland is noticeably cooler than craft that don't have foam insulation. We have 2"-3" from floor level up. Partition bulkheads are made of that 1.1/2" (comes in other thicknesses) foam insulation material with silver foil on either side, sandwiched between thin ply. This allows us to keep e.g. the saloon area warm in winter while keeping the bedroom rather cooler.

[blackrose]

Except that foam spray also keeps a boat cooler in the summer too - Friesland is noticeably cooler than craft that don't have foam insulation. We have 2"-3" from floor level up. Partition bulkheads are made of that 1.1/2" (comes in other thicknesses) foam insulation material with silver foil on either side, sandwiched between thin ply. This allows us to keep e.g. the saloon area warm in winter while keeping the bedroom rather cooler.

 

Yes, that's true.

 

Any thermal insulation will help to keep a boat cooler in summer, and PU foams (either sprayed or in sheet form) are pretty good, but sprayfoam and other insulation materials don't work as well in summer to keep a steel boat cool as they do in winter to keep the heat in.

 

You have to think of the complete cross-section, comprised of steel sheet, a layer of foam and the wooden lining. In winter, warm air inside the boat comes up against the wooden lining and slowly heats the cavity but the foam significantly reduces heat transfer to the steel behind it. However, in summer the sun beats down on the steel making it almost too hot to touch (in winter the warm air coming into contact with the foam is never this hot!) The sprayfoam is actually bonded to the steel and so heat transfer is increased and even fairly thick cross-sections of foam will not be nearly as efficient in keeping heat out of the boat, as thinner cross-sections are in keeping the heat in.

 

I have areas on my boat where the sprayfoam is a lot less than 1" thick and other areas below the gunwale where it's more like 3" thick. Yet today with the sun beating down on the side of the boat, both areas of the internal wooden lining feel equally warm and I get similar readings on my IR thermometer.

Edited July 24, 2012 by blackrose

[ditchcrawler]

I often wonder the true benefit when you consider that on lots of narrowboats at a guess over 25% of the area of the cabin side is single glazed glass. Caravans went for double glazing years ago and they use plastic which has better thermal properties than glass to start with. I dont think they use spray foam in caravan walls.

[blackrose]

I often wonder the true benefit when you consider that on lots of narrowboats at a guess over 25% of the area of the cabin side is single glazed glass. Caravans went for double glazing years ago and they use plastic which has better thermal properties than glass to start with. I dont think they use spray foam in caravan walls.

 

Not to mention all the mushroom vents and other non-closeable vents that we have on boats. Over a certain thickness of foam it really is an issue of diminishing returns.

[mrsmelly]

I often wonder the true benefit when you consider that on lots of narrowboats at a guess over 25% of the area of the cabin side is single glazed glass. Caravans went for double glazing years ago and they use plastic which has better thermal properties than glass to start with. I dont think they use spray foam in caravan walls.

 

Went to look at a collingwood sailaway with a friend yesterday There was about 2mil in most places, and in large expances we could see the primed steel underneath. Totaly inadequate by anyones measure and a total rip off, that and the steelwork very quickly led my friend to walk away as I suggested he would before we even got there.

 

Tim