Sprayfoam thickness

[Frankieboy]

Evening all,

A simple question (I think). It seems that sprayfoam always seems to be an inch thick (or the sprayers guarantee a minimum of an inch). Now I have 2 " gap all round now its battonned out so am looking to get 2" thick of sprayfoam.

I figured if the space is there fill it.

Does this make sense? Ive heard of people saying you need an air gap but cant think what benefits this would have.

Obviously it costs more for thicker foam but will be toastier in the long run.

A sound theory or not?

[mykaskin]

Evening all,

A simple question (I think). It seems that sprayfoam always seems to be an inch thick (or the sprayers guarantee a minimum of an inch). Now I have 2 " gap all round now its battonned out so am looking to get 2" thick of sprayfoam.

I figured if the space is there fill it.

Does this make sense? Ive heard of people saying you need an air gap but cant think what benefits this would have.

Obviously it costs more for thicker foam but will be toastier in the long run.

A sound theory or not?

 

Very, it's more or less what my Dad did.

[Nickhlx]

Very, it's more or less what my Dad did.

 

Echoed - I wish I had ( been able) to increase the insulation thickness on ours... especially with fuel prices escalating as they are and will for ever more - possibly double glazing next !

 

Nick

[blackrose]

Bear in mind the law of diminishing returns.

 

2" of sprayfoam does not give you twice the thermal insulation of 1". I don't have the figures but I'd be surprised if the extra inch even provided 10% more insulation (in fact it's probably a lot less than that).

 

As for the airgap - lots of people say you need it to provide airflow and an airspace for any water in the bilges to evaporate into. Yes, a closed cavity providing airflow or evaporation space sounds nonsensical to me too and in my opinion that's exactly what it is.

 

Edit: If you want to find out how much extra insulation 2" of foam provides over 1" thickness why not contact the manufacturers of Cellotex or Kingspan - the PU board they make is essentially the same stuff. It comes in 25mm & 50mm thicknesses (I think?) and I'm sure they will have the figures. I'd be interested to know.

Edited February 4, 2011 by blackrose

[system 4-50]

Evening all,

A simple question (I think). It seems that sprayfoam always seems to be an inch thick (or the sprayers guarantee a minimum of an inch). Now I have 2 " gap all round now its battonned out so am looking to get 2" thick of sprayfoam.

I figured if the space is there fill it.

Does this make sense? Ive heard of people saying you need an air gap but cant think what benefits this would have.

Obviously it costs more for thicker foam but will be toastier in the long run.

A sound theory or not?

Actually the challenge is to get them to do the one inch over all the metal. After mine had been done I found a lot was missing behind most angle iron components. Don't let them start clearing up until you've inspected it thoroughly - which you can do within just a few minutes of it being sprayed, it sets that fast.

[ditchcrawler]

Actually the challenge is to get them to do the one inch over all the metal. After mine had been done I found a lot was missing behind most angle iron components. Don't let them start clearing up until you've inspected it thoroughly - which you can do within just a few minutes of it being sprayed, it sets that fast.

They came all the way from Wales to Suffolk to re-do mine

Edit to add

A pice of thin ply about 50mm square with a nail driven through it by 1-2 inches makes a good depth gauge.

Edited February 4, 2011 by ditchcrawler

[steelaway]

Evening all,

A simple question (I think). It seems that sprayfoam always seems to be an inch thick (or the sprayers guarantee a minimum of an inch). Now I have 2 " gap all round now its battonned out so am looking to get 2" thick of sprayfoam.

I figured if the space is there fill it.

Does this make sense? Ive heard of people saying you need an air gap but cant think what benefits this would have.

Obviously it costs more for thicker foam but will be toastier in the long run.

A sound theory or not?

 

 

Hi

 

They should spray to be level with the battons, wether it 1", 2" or 3".

They dont/cant always get it right the first time, I had to have them back because it was down below the battons the first time.

They will also spray the engine room and under the catch if you tell them

 

websters.

 

Alex

[gillian]

doesn't the gap have something to do with avoiding condensation? I am no physicist but it does ring a bell?????

[nb Innisfree]

Evening all,

A simple question (I think). It seems that sprayfoam always seems to be an inch thick (or the sprayers guarantee a minimum of an inch). Now I have 2 " gap all round now its battonned out so am looking to get 2" thick of sprayfoam.

I figured if the space is there fill it.

Does this make sense? Ive heard of people saying you need an air gap but cant think what benefits this would have.

Obviously it costs more for thicker foam but will be toastier in the long run.

A sound theory or not?

 

No airgaps are needed better to fill any gaps with foam but to get a minimum thickness all over will entail a lot of foam being sprayed too thickly which will involve a lot of arduous and messy cutting back later.

[blackrose]

doesn't the gap have something to do with avoiding condensation? I am no physicist but it does ring a bell?????

It only rings a bell because it's something incorrect that you've heard. Condensation forms when moisture contained in warm air hits a cold surface. If the cold surface (steel hull) is properly insulated it makes no difference whether you place a sheet of ply up against the insulation or 1" away from it. Also, in the case of the latter the cavity created will not provide any additional ventilation since it is a closed space.

[ChrisPy]

If you get at least 1" thickness applied to the sides and ceiling of the cabin space, any increase in thickness will give only marginal improvements, because most heat will then be lost through vents, window glass and frames, doors, etc.

 

I do not understand the references to messy cutting back, so often seen when discussing sprayfoam. Clearing up just needs a snow shovel, several big bin bags, followed by a vac. The only problem was bits getting down the sides beyond the edge of the flooring panels, obstructing the bilges, but a good suck with the vac will pull them out.

 

If the battens are 2" and the nominal thickness of the foam is 1" then cutting back is only required at the battens, frames, etc. I used a long flexible breadknife and cut back my 42ft cabin in less than one day.

[rjasmith]

I agree with ChrisPy about not needing thicker than 1". Some Sprayfoam firms supply a data sheet that gives calculations showing how relatively small the advantage is for foam thicker than 1" (I used A & K Insulation and they certainly issue a sheet which covers this and many other helpful bits of info about sprayfoam in boats). Perhaps other firms do the same.

 

I looked on the A & K website, the sheet isn't on there unfortunately but I'm sure they'd let you have a copy if you gave them a ring.

 

On the subject of masking up/cutting back - don't do as I did and buy a cheapo make of parcel tape to do the masking (from Screwfix). It was fine pulling it off the battens but wherever I had covered a smooth surface eg brass porthole frames, plastic cable trunking etc, the cheap stuff always left its adhesive behind which then needed cleaning off with cellulose thinners. Cutting back was quick, cleaning the sticky adhesive off was not!!

 

I had run out of the cheap tape towards the end of masking up and got some more to finish it from a local shop. This was proper 3M stuff and although not a lot more expensive it pulled off cleanly everywhere.

 

For cutting back I ground the teeth off an old handsaw to make a superbly bendy long knife which made the job really easy.

 

Richard

[RLWP]

Not specifically for narrowboats, but this site has a chart

 

0.5" to 1.5" for a metal building. I'm assuming that sprayfoam is closed cell?

 

Richard

[system 4-50]

The cutting back on my boat was done by the sprayers. They used a saw ie with teeth. The result is a continuous fine shower of descending foam dust that still comes down months later. I will have to take measures against this when I come to varnish my panels. [i haven't got as far as doing the panelling yet.] It is a profound nuisance. I suspect but I don't know for certain that using a knife or sharp blade as opposed to a toothed tool would not do this. An old bread knife perhaps?

[Nickhlx]

The cutting back on my boat was done by the sprayers. They used a saw ie with teeth. The result is a continuous fine shower of descending foam dust that still comes down months later. I will have to take measures against this when I come to varnish my panels. [i haven't got as far as doing the panelling yet.] It is a profound nuisance. I suspect but I don't know for certain that using a knife or sharp blade as opposed to a toothed tool would not do this. An old bread knife perhaps?

 

Could the "finished / cut back surface not be sprayed with a weak solution of PVA ( water based) to bind the surface dust ?

 

Nick

[soldthehouse]

I havnt read all replies, but as I understand it from when we had a huge potato store sprayed, It is such an imprecise art that they are guessing the final thickness as they go. The stuff we had put on went on like treacle and foamed up in a few minutes. How they are supposed to judge how much to put on and what the finished thickness will be is just guess work even for the most experienced technician. I was quoted for 1" and 1 1/2" finish and the difference was substantial. When I asked the sprayer afterwards how he would have judged the difference he shrugged his shoulders and said dunno you tell me!

Edited February 5, 2011 by soldthehouse

[blackrose]

Not specifically for narrowboats, but this site has a chart

 

0.5" to 1.5" for a metal building. I'm assuming that sprayfoam is closed cell?

 

Richard

 

Predominantly, yes.

 

I havnt read all replies, but as I understand it from when we had a huge potato store sprayed, It is such an imprecise art that they are guessing the final thickness as they go. The stuff we had put on went on like treacle and foamed up in a few minutes. How they are supposed to judge how much to put on and what the finished thickness will be is just guess work even for the most experienced technician. I was quoted for 1" and 1 1/2" finish and the difference was substantial. When I asked the sprayer afterwards how he would have judged the difference he shrugged his shoulders and said dunno you tell me!

 

So I guess you wait until he's finished, go around with a long nail on a stick and then tell him if it's not up to spec. Is there any problem with spraying on top of cured foam? I'm sure it sticks to itself.

[Frankieboy]

Or another option wuld be to get 1.5" sprayfoam and then put a sheet of the insulating bubble foil over the top.

As theres a 2" gap it seems absolutely daft just to put an inch of foam in there and then complain about cold in winter.

Would 1.5" sprayfoam then the foil cover be a wise option?

[blackrose]

Or another option wuld be to get 1.5" sprayfoam and then put a sheet of the insulating bubble foil over the top.

As theres a 2" gap it seems absolutely daft just to put an inch of foam in there and then complain about cold in winter.

Would 1.5" sprayfoam then the foil cover be a wise option?

 

That's not a bad idea (and probably cheaper than all that extra foam). If the bubble foil is only single-sided you fit it foil side facing in and you'd have to make sure that there's at least a small airgap between the silver foil and the wood lining. If there's no gap then the silver reflective foil doesn't work.

[soldthehouse]

Predominantly, yes.

 

 

 

So I guess you wait until he's finished, go around with a long nail on a stick and then tell him if it's not up to spec. Is there any problem with spraying on top of cured foam? I'm sure it sticks to itself.

I found that the thickness applied to the building we had done was way over the specified thickness and very inconsistent in thickness also. The company was from the Hull area I think and they did narrowboats too. It was in the early nineties. I dont think they would have appreciated someone going around with a depth gague and saying could you put a little more there and a little more there. I personally am of the opinion that a covering of any thickness on a narrowboat or wideboat would do the job, as to me the main point is to create a thermal barrier to condensation and even if the foam was say 3/4" thick, this combined with the lining out and air gap would give a good level of heat retention. I suspect heat loss per se is actually not as critical as some make out and that most boats generate more heat than is actually required for comfort.

Edited February 5, 2011 by soldthehouse

[nb Innisfree]

If you get at least 1" thickness applied to the sides and ceiling of the cabin space, any increase in thickness will give only marginal improvements, because most heat will then be lost through vents, window glass and frames, doors, etc.

 

I do not understand the references to messy cutting back, so often seen when discussing sprayfoam. Clearing up just needs a snow shovel, several big bin bags, followed by a vac. The only problem was bits getting down the sides beyond the edge of the flooring panels, obstructing the bilges, but a good suck with the vac will pull them out.

 

If the battens are 2" and the nominal thickness of the foam is 1" then cutting back is only required at the battens, frames, etc. I used a long flexible breadknife and cut back my 42ft cabin in less than one day.

 

Clearing up is easy it's the trimming back that is hard work, there's only room for just over 1" of foam on a standard nb ceiling if you want 6' 5" headroom, so trying to get an even thickness of foam will involve quite a bit of over thickness applied to ensure a minimum of 1" and that results in a lot of foam removal.

[noff]

Could you not fill the 'gap' between lining and 1'' foam with Rockwall type material ?

[ditchcrawler]

Could you not fill the 'gap' between lining and 1'' foam with Rockwall type material ?

Why?

[blackrose]

Could you not fill the 'gap' between lining and 1'' foam with Rockwall type material ?

 

Yes, some people add rockwool before lining out. Since the vapour barrier is already there in terms of the sprayfoam, it will not be subject to any problem of moisture passing through to form condensation on the hull - a criticism some people cite as a problem of using only rockwool on a steel hull.

 

Again, how much insulation benefit you'll actually get over a 1" thickness of sprayfoam is probably very marginal. All that insulation will not prevent your windows and vents letting the heat out the same as any other boat, so at that point if you want to improve the boat's insulation it would probably be better to start looking at double glazing.

Edited February 6, 2011 by blackrose

[Frankieboy]

We only have 8 small portholes on our boat and then a few vents, so no big bus windows to let huge amounts of heat out.

I used to work on refineries that used rockwool insulation on piping and my honest opinion of it is that its absolutely crap. Fair enough it keeps heat in / out, but at the very sign of moisture it seems to "clump" up and fall to the bottom of the void which it is in. I would advise getting something better such as a sheet of insulatiojn or such.