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how thick should spray foam be?


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that is all!

 

As thick as you want it. Just remember that your battens & Bearers must be deep enough to accommodate it, and that insulation reaches a point of diminishing returns.

 

Ours is 75 - 85mm - - and I'm very happy with that.

 

(and the thicker the insulation - the less space you have inside the boat, of course

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you'll notice a huge improvement with just 25mm, and that should allow normal battens, etc. to be used.

 

there was a recent thread where the relative benefits of thicker insulation were discussed. Try a search of the forum.

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thanks all. do you know if the spray companies will do any thickness we want? i am using 38mm battens and am wondeing if i should fill the whole void or leave a bit for wiring etc. also no need for shaving it all back if there's a bit of a gap!

 

The trick with spray foam is not necessarily the thickness although obviously thicker the better. However it's the evenness of the foam that's more important, as dips bumps and thin areas cause cold spots which reduces it's thermal efficiency by quite some margin. Some think spray foam is the be all and end all of all insulation, but if it's uneven it'll perform less well than most other types of insulation that are applied evenly with no air gaps.

 

 

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yes thanks julynian that makes sense. i've been trying to avoid cutting sections out for wiring etc for exactly that reason, so have a zone of around 10mm for wires between foam and ply lining. that said, i was wondering if i should fill the void right up, and cut the grooves out anyway. this would improve thermal performance i'm sure, but all the blogs i read reckon cutting the foam is the worst bit of the whole job!

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yes thanks julynian that makes sense. i've been trying to avoid cutting sections out for wiring etc for exactly that reason, so have a zone of around 10mm for wires between foam and ply lining. that said, i was wondering if i should fill the void right up, and cut the grooves out anyway. this would improve thermal performance i'm sure, but all the blogs i read reckon cutting the foam is the worst bit of the whole job!

 

If i was fitting out a new boat I would fit ducts in pvc tubes for all the wiring and spare ducts for other things and sprayfoam them in behind. At least then if you need to modify the wiring and run new wires you can pull them through.

 

James :cheers:

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yes thanks julynian that makes sense. i've been trying to avoid cutting sections out for wiring etc for exactly that reason, so have a zone of around 10mm for wires between foam and ply lining. that said, i was wondering if i should fill the void right up, and cut the grooves out anyway. this would improve thermal performance i'm sure, but all the blogs i read reckon cutting the foam is the worst bit of the whole job!

 

Ideally the sprayfoam should swell beyond the battens, cutting it back is a pain I've heard, I used Rockwool. If you can find a nice long saw blade, old Diston saw or alike, remove old handle and fix saw blade to a flat piece of wood, ply or 4 x 1 timber, as long as the blade spans the ribs you'll get perfect straight cuts by using the battens as a guide, lot of mess to clear up, but a job well done. Any areas you need to cut out for access you can fill with large tins of spray foam, you can buy a sprayfoam kit from Screwfix for a decent price, comes in handy for all sorts of jobs whilst fitting out.

 

I'm not sure about filling grooves with sprayfoam that have cable in though, what you can do though is fill these gaps with rockwool or fibreglass insulation and tape over the void with aluminium tape you can get it up to 3 inches wide even 4 I think, it will seal in the loose insulation but leave cables accessible if need be in the future, plus you'll know where the cables are as the alloy tape will be clearly visible.

 

 

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Fix the battens first, and electrical conduit if desired. Then put masking tape on the face of all the battens before sprayfoaming. Makes it much easier to remove foam from the battens, which then form the datum for trimming back any overspray elsewhwere, as already described.

Edited by David Mack
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yes thanks julynian that makes sense. i've been trying to avoid cutting sections out for wiring etc for exactly that reason, so have a zone of around 10mm for wires between foam and ply lining. that said, i was wondering if i should fill the void right up, and cut the grooves out anyway. this would improve thermal performance i'm sure, but all the blogs i read reckon cutting the foam is the worst bit of the whole job!

 

 

 

As thick as possible - I made my sprayers come back and put some more after this - not up to the tops of battens - see photo

Cutting back a small price to pay for thick insulation and it easily cut with a bread knife --- See photo.

But mask the battens.

 

Alex

 

DSCF2016-1.jpg

 

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As thick as possible - I made my sprayers come back and put some more after this - not up to the tops of battens - see photo

Cutting back a small price to pay for thick insulation and it easily cut with a bread knife --- See photo.

But mask the battens.

 

Alex

 

DSCF2016-1.jpg

 

How thick are those battens?

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As thick as possible - I made my sprayers come back and put some more after this - not up to the tops of battens - see photo

Cutting back a small price to pay for thick insulation and it easily cut with a bread knife --- See photo.

But mask the battens.

 

Alex

 

DSCF2016-1.jpg

Same here, they came from Wales to Suffolk at their expense to redo mine, it was like a coat of paint in places. A pin driven through a small square of thin ply makes a good depth gauge.

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Ours is 75 - 85mm - - and I'm very happy with that.

 

 

Are you sure? That's about 3 to 3 & 1/2 inches thick! I've never heard of anyone putting sprayfoam on that thick.

 

You know your boat so you might be right, but in my experience most people have a habit of over-estimating the thickness of their sprayfoam.

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Hi

 

I used 2"x2" below the gunnel's and 1" above.

You can see there was definitely not to spec below the gunnel's

 

Alex

 

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.

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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.

 

So that's how you spell 'gunwhales' I can never remember.blush.gif

Also 9mm ply and thick carpet below gunwhalestongue.gif

 

Alex

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