Spray foam vs Celotex

[Sphinx123]

Hey everyone! We are insulating our boat next month and torn between closed cell spray foam or celotex. Many people say spray foam is best for boats, but I'm starting to see a lot of people saying celotex is just as good provided it's a tight fit with no air gaps. Celotex would be faster for us to fit because the spray foam requires more prep work beforehand. But I don't mind investing in spray foam and giving it the extra time if it's really worth it. 

 

So, celotex or spray foam - what are your thoughts?

[TheBiscuits]

It's been widely discussed on here.  Search the forums for Kingspan or Celotex and you'll have plenty to read.

 

Short answer: spray foam is faster (= cheaper for boatbuilders) and is good. 

 

Foil faced insulation boards provide better long term insulation (after a few years) because they're the same stuff with a reflective barrier both sides.

 

If it's a refit a bit at a time, boards win outright because you can sensibly do them in stages.  For a completely bare steel boat it's down to personal preference.

[GUMPY]

Spray foam for me, no air gaps, someone else does the difficult bit all that I had to do was batten out the hull and that's quick and easy if you use a nail gun. 😉

[BEngo]

Spray foam guarantees a vapour barrier, so no condensation on the steel. It also helps to hold the battens to the frame.  Celotex etc. can achieve a vapour barrier but it requires careful fitting and lots of taping and gun foam work.  It does not help hold the battens on.

Spray foam needs cutting back and the applicators need to be good, so as to get it applied to an adequate and even thickness.  There are rumours of foam companies that skimp....Cutting back is easy but takes a lot of time and makes a lot of mess.

 

We went foam, in 1989, and it has been good ever since.  I would go foam again.

 

N

[blackrose]

For diy then it's cellotex or kingspan boards; for contractors it's sprayfoam if done properly. 

 

Foil facing only makes a difference on the exposed side if there's an airgap. For the side that's bonded to the steel the foil facing doesn't do anything.

[Tracy D'arth]

I have seen plenty of spray foam peeling off. I which case it may as well not be there. I have also seen lots scrimped and far too thin.

 

Kingspan for me every time.  And fill any gaps with can foam.  With care it can be a splendid job.

[beerbeerbeerbeerbeer]

Why don’t Rockwool get used any more?

That’d be easier to ensure no gaps, wouldn’t it?

Overlaps easy and easily compressed. 
 

🤷‍♀️

[Tracy D'arth]

3 minutes ago, Goliath said:

Why don’t Rockwool get used any more?

That’d be easier to ensure no gaps, wouldn’t it?

Overlaps easy and easily compressed. 
 

🤷‍♀️

If compressed it is less efficient. It can soak and hold moisture. It shakes down and doesn't stay where it needs to be.

[PCSB]

18 minutes ago, Goliath said:

Why don’t Rockwool get used any more?

That’d be easier to ensure no gaps, wouldn’t it?

Overlaps easy and easily compressed. 
 

🤷‍♀️

Celotex (and Kinspan etc inc sprayfoam) is about twice as good an insulator at the same thickness.

[blackrose]

13 minutes ago, Tracy D'arth said:

If compressed it is less efficient. It can soak and hold moisture. It shakes down and doesn't stay where it needs to be.

 

Yes and if installing rockwool them you also need to install a vapour barrier. It's just as much work as installing kingspan or cellotex and much less efficient.

[beerbeerbeerbeerbeer]

12 minutes ago, Tracy D'arth said:

If compressed it is less efficient. It can soak and hold moisture. It shakes down and doesn't stay where it needs to be.

I weren’t think of squashing flat but just pushing edges close together.
But yes, I forgot it can hold moisture.

I dragged a lot out from under my floor which was a mess after being there for years.

But as far as I can tell in the walls it has stayed nice and dry, and remained in place.

4 minutes ago, PCSB said:

Celotex (and Kinspan etc inc sprayfoam) is about twice as good an insulator at the same thickness.

Fair point

[cuthound]

My boat wass insulated with 3M Thinsulate from new.

 

Glues to the steel and has a built in vapour barrier.

 

Virtually as efficient as spray foam for thermal insulation with better sound insulation.

 

Easy to retro fit DIY.

 

15 years old and still as good as new.

[Slow and Steady]

3 minutes ago, cuthound said:

My boat wass insulated with 3M Thinsulate from new.

 

Glues to the steel and has a built in vapour barrier.

 

Virtually as efficient as spray foam for thermal insulation with better sound insulation.

 

Easy to retro fit DIY.

 

15 years old and still as good as new.

Mine too - I'm not seeing the vapour barrier though and IMO it's terrible - it's a sound proofing material for cars, 3M do not provide thermal insulation numbers for it or describe it as thermal insulation.

[Chris Lowe]

I would think Kingspan kooltherm k15 would probably be a good one to use, it's rainscreen insulation so the outer face acts as a vapour barrier.

[cuthound]

Just now, Slow and Steady said:

Mine too - I'm not seeing the vapour barrier though and IMO it's terrible - it's a sound proofing material for cars, 3M do not provide thermal insulation numbers for it or describe it as thermal insulation.

 

Why do you think it is terrible? Was yours not installed properly?

 

3M certainly used to publish insulation figures for the marine insulation. Mine is about 50mm thick. How thick is yours, the van insulation is much thinner.

 

There sides are two different colours. iIRC the darker side is a vapour barrier.

 

https://www.marineindustrial.co.uk/Catalogue/Thermal-Acoustic-Insulation/3M/Thinsulate

 

 

[Slow and Steady]

11 minutes ago, cuthound said:

 

Why do you think it is terrible? Was yours not installed properly?

 

3M certainly used to publish insulation figures for the marine insulation. Mine is about 50mm thick. How thick is yours, the van insulation is much thinner.

 

There sides are two different colours. iIRC the darker side is a vapour barrier.

 

https://www.marineindustrial.co.uk/Catalogue/Thermal-Acoustic-Insulation/3M/Thinsulate

 

 

Yes, it's supposed to expand isn't it. I suspect mine was cheap van stuff. I'm just not impressed. Probably dandy for a holiday boat, not so good through the winter.

Fag papers for scale.

 

[Hudds Lad]

Just now, Slow and Steady said:

Yes, it's supposed to expand isn't it. I suspect mine was cheap van stuff. I'm just not impressed. Probably dandy for a holiday boat, not so good through the winter.

Fag papers for scale.

 

You could always use it for filters  

[cuthound]

6 minutes ago, Slow and Steady said:

Yes, it's supposed to expand isn't it. I suspect mine was cheap van stuff. I'm just not impressed. Probably dandy for a holiday boat, not so good through the winter.

Fag papers for scale.

 

 

Although a holiday boat, I often use it in the winter.

 

With the Kabola Old Dutch oil drip stove on setting 2, the inside of the 60 foot boat stays above 23°C even when the outside temperature is well below freezing and the cut frozen over.

[Slow and Steady]

27 minutes ago, cuthound said:

 

Why do you think it is terrible? Was yours not installed properly?

 

3M certainly used to publish insulation figures for the marine insulation. Mine is about 50mm thick. How thick is yours, the van insulation is much thinner.

 

There sides are two different colours. iIRC the darker side is a vapour barrier.

 

https://www.marineindustrial.co.uk/Catalogue/Thermal-Acoustic-Insulation/3M/Thinsulate

 

 

Found it. Mine is the thinner stuff no doubt.

R value 3.8 at 26 mm thickness

R value 5.8 at 44 mm thickness

Technically very good actually!*

Celotex R value  2.25 at 50mm

* I'm thinking there are cunning ways of specifying this. The celotex specifies "2kw", the 3M is quiet on that aspect. I don't know what it means I'm just suspicious that it could be like battery capacity discharge rates.

Edited May 12, 2022 by Slow and Steady

[TheBiscuits]

10 minutes ago, Slow and Steady said:

I'm thinking there are cunning ways of specifying this. The celotex specifies "2kw", the 3M is quiet on that aspect. I don't know what it means I'm just suspicious that it could be like battery capacity discharge rates.

 

Nah, the units for R values are Metres squared Kelvin per Watt, m²·K/W

 

It's probably just a badly formatted web page that can't handle what was pasted into it.

 

 

 

Edited May 12, 2022 by TheBiscuits
clarity

[Slow and Steady]

2 minutes ago, TheBiscuits said:

 

Nah, the units for R values are Metres Squared Kelvin per Watt, m²·K/W

 

It's probably just a badly formatted web page that can't handle what was pasted into it.

Thanks, that makes sense!

I'm still highly suspicious that it's apparently almost 3x better than celotex - if it were that good everybody would use it!

Edited May 12, 2022 by Slow and Steady

[jonathanA]

20 minutes ago, Slow and Steady said:

Thanks, that makes sense!

I'm still highly suspicious that it's apparently almost 3x better than celotex - if it were that good everybody would use it!

Maybe its 3 times as expensive .. 🤔 

[TheBiscuits]

16 minutes ago, jonathanA said:

Maybe its 3 times as expensive .. 🤔 

 

More like 5 I would have thought.

[Slow and Steady]

1 hour ago, TheBiscuits said:

 

More like 5 I would have thought.

I was chatting with someone yesterday who spent £1500 on it for his camper. I priced Celotex up for my 60ft boat inc tape and it was around £1,000!

Point being that thin is all there is room for in a boat to maximise the internal space so you'd think people would get their wallets out.

[Tracy D'arth]

Has anyone ever worked out the U or the R value of  "about"  25mm of badly applied spray foam?