Prepping for celotex insulation

[LeonR]

Hi all, 

Just about to start work on our first boat and turning a storage space at the front into a small bedroom for our 2 year old... After much reading I think I'm going to go forth celotex, tape, expanding foam combo. Do I need to prep the metal in any way?

 

Its a 120 year old dutch barge so the area I'm talking about is right at the bow end behind a bulkhead. Been a store for 120 years... Just wondering what's necessary. 

Thanks in advance!

Leon

[Tony Brooks]

At least remove as much of any existing rust as you can, and as Celotex is a fairy stiff slab material, and on a hull with compound curves you are likely to have at least some voids beneath it, I would apply a rust "resistant" paint system, so the hull does not rust beneath the Celotex where you can't see it.

[LeonR]

Do you think those voids should be packed with anything? 

 

Thanks for the response, appreciated.

[Tony Brooks]

30 minutes ago, LeonR said:

Do you think those voids should be packed with anything? 

 

Thanks for the response, appreciated.

so, how will you do that? They are likely to form when you push a fairly solid sheet onto a compound curved hull. It all depends on how stiff the Celotex, is and the degree of curve.

 

Seeing you say at the bow, then I would expect fairly sharp horizontal and vertical curvature of the hull. If you forced Celotex to fit tight, my guess is that it would split open in a number of places. Spray foam would probably do better.

[Onewheeler]

Are you sure that you won't need any welding done on the hull in the near future (at 120 y.o. it's a routine thing at docking)? You'll likely need to strip the celotex out first.

[LeonR]

@Onewheeler Shouldn't need to as the bow end and engine rooms seem to have a layer of grease allover the steel which has protected it well. You can't say the same about other areas unfortunately! The hull has already been doubled so when that goes I think the boat goes. She's a bit of a gamble. I've heard people say that they have welded with celotex in situ and nothing has gone up in flames..

 

@Tony Brooks Some kind of malleable material (rock wool or sheeps wool) I'm just thinking about reducing any condensation in the gaps, because as you said its a hefty curve. I really want to avoid the faff and expense of a full spray foam job. Otherwise I score the boards to allow them to bend (filling and taping the back). Maybe thinking a bit too deeply? 

@Tony BrooksAnyway, back to the original question, and thanks for answering so far - do you have recommendations for cheap/good rust resistant paint and fireproof expanding foam? I've done lots of little building projects in my life but never on a boat, so just trying to figure out if the materials are all generally the same? Also, is there good go-to suppliers for boat building supplies? I've built food trucks and knowing where to go for catches, brackets etc is really handy. 

I saw I can can buy bloody portholes on Amazon haha. 

[Tony Brooks]

38 minutes ago, LeonR said:

@Onewheeler Shouldn't need to as the bow end and engine rooms seem to have a layer of grease allover the steel which has protected it well. You can't say the same about other areas unfortunately! The hull has already been doubled so when that goes I think the boat goes. She's a bit of a gamble. I've heard people say that they have welded with celotex in situ and nothing has gone up in flames..

 

@Tony Brooks Some kind of malleable material (rock wool or sheeps wool) I'm just thinking about reducing any condensation in the gaps, because as you said its a hefty curve. I really want to avoid the faff and expense of a full spray foam job. Otherwise I score the boards to allow them to bend (filling and taping the back). Maybe thinking a bit too deeply? 

@Tony BrooksAnyway, back to the original question, and thanks for answering so far - do you have recommendations for cheap/good rust resistant paint and fireproof expanding foam? I've done lots of little building projects in my life but never on a boat, so just trying to figure out if the materials are all generally the same? Also, is there good go-to suppliers for boat building supplies? I've built food trucks and knowing where to go for catches, brackets etc is really handy. 

I saw I can can buy bloody portholes on Amazon haha. 

 

I would never use any sort of fibrous type insulation inside a boat, seen too much sodden Rockwall/glass fibre insulation over the years. I have no idea how you can fill and tape the back of the boards where they are against the hull, they need pushing against the hull because as soon as you would need to keep the boards exactly in shape while you lift them away from the hull and invert them for the filling and taping. If you think that you can, then that should work well. I doubt that you would avoid voids against the hull if did cut it into squares, glued it on leaving a (say) 6mm gap all round and filling the gaps with gun foam.

 

You now say the hull at the bow has been greased, and that presents more problems in reaction to adequately cleaning it so adhesive and/or paint will stick long term.

 

After Grenfell Tower, we know that Celotex type foams are only fire-resistant to a certain degree but we are also told a good welder can over plate a boat with spray foam on the hull. That is not true for expanded polystyrene, even the fire-resistant grade. I also don't know of any paint that is fire-resistant apart from whitewash or cement wash. Even without the grease, the chances of you totally removing the rust without a very noisy needle gun or sand blasting is, I suggest, about zero, so you would only be trying to slow further rusting with paint. It is a case of do your best. Apart from branding and the customary "marine" price premium, I think the materials are about the same, but you can't compare the rust resistance of A4 and A2 stainless steel or brass plated steel and brass/bronze.

 

I can't recommend a paint system, because its longevity all depends on your preparation, and I don't know enough about foamed sheets to say any more than I have already.

[LeonR]

@Tony BrooksThanks a lot. I reckon I have enough to get cracking with the preparation now. 

[blackrose]

15 hours ago, LeonR said:

Do you think those voids should be packed with anything? 

 

Thanks for the response, appreciated.

 

If you spray some hand held foam onto the back of the cellotex and use it as adhesive it will fill the voids. You may need to prop the boards in place until the sprayfoam sets. Acroprops seem a bit too heavy duty, not sure what other form of adjustable props you could use?

[harrybsmith]

I've just Celotexed much of the inside of my shell, process was (cabin top and sides):

-Scrape off loose rust, scuff over with a disc sander

-Vactan

-Zinc Phos primer

-Paint with any old exterior gloss I had, great way of using up odds and ends

-Batten sides to allow lining to be fitted later

-Cut Celotex to size and score reverse side with a Stanley blade 

-Gun on this stuff to back of Celotex

(https://www.selcobw.com/bond-it-mega-foam)

-Apply pressure from a bit of 4*2 cut to length, leave it 15 mins, do the next bit

 

A full write up will eventually happen on my build thread, I promise...

[blackrose]

2 hours ago, Tony Brooks said:

After Grenfell Tower, we know that Celotex type foams are only fire-resistant to a certain degree 

 

Well we knew that before Grenfell. Any foam material is only fire resistant to a certain degree and fire resistant celotex manufactured under controlled factory conditions is likely to fare better than fire resistant spray foam applied fairly randomly by some Herbert in a boat yard. Even if the base PU polymer is the same the way it's applied will have a bearing on flammability.

Edited November 21, 2023 by blackrose

[nicknorman]

Just to mention in case you didn't know, that there are different grades of can spray foam. The ordinary stuff which has a high degree of expansion and not much strength, or the builders adhesive foam which is stronger and expands a lot less (and needless to say is more expensive). If you are going to use the foam to stick the boards to the steel, then use the latter so that the boards don't get pushed off when the foam expands. At a pinch and if there are awkward cavities left, you could drill a hole in the foam sheet and inject a small amount of builders foam. Very small amounts, otherwise it will expand and push the sheets off!

[LeonR]

@nicknorman Monstrous! Great tips. Thanks! 

 

@harrybsmithThanks, I am literally going to use your list. Lovely stuff!

[David Mack]

53 minutes ago, harrybsmith said:

Cut Celotex to size and score reverse side with a Stanley blade 

Why on the reverse side? If you have a curved surface on a boat it is going to be concave seen from the inside. So scoring the back will result in narrow voids opening up in the back face. If you cut narrow slits, or better v-grooves the inside face these will close up when you curve the sheet, and after the sheets have been bonded to the shell you can tape over the slits using the same metallised tape you use to endure a continuous vapour barrier over board joints.

[truckcab79]

On 21/11/2023 at 11:26, LeonR said:

@nicknorman Monstrous! Great tips. Thanks! 

 

@harrybsmithThanks, I am literally going to use your list. Lovely stuff!

These chaps are bang on with their suggestions and although I don’t have the curves you are dealing with is how I plan to insulate mine.  Screwfix adhesive foam is decent.  Buy gun foam and a gun, not the disposable cans.  Soudal make a fire rated foam but it’s not ‘fire-proof’ so I wouldn’t bother.  Screwfix expanding foam, gun grade is again good. Don’t buy their guns though.  They’re fine but £25. ToughMaster on Amazon. £15 delivered and better quality.  👍
 

Ignore Kingspan for your Celotex.  Most builders merchants stock an off-brand version at a fraction of the price.  Kingspan 40mm at Wickes is about £37. Lawsons sell basically the same stuff without the logo for almost half. If you can get a trade account even better, though there is no fixed discount, you’ll just get treated better the more you spend and the better your relationship with your account manager.  Mine costs me a £100 bottle of whisky at Christmas. Worth every penny. 👍😂

[harrybsmith]

On 21/11/2023 at 11:38, David Mack said:

Why on the reverse side? If you have a curved surface on a boat it is going to be concave seen from the inside. So scoring the back will result in narrow voids opening up in the back face. If you cut narrow slits, or better v-grooves the inside face these will close up when you curve the sheet, and after the sheets have been bonded to the shell you can tape over the slits using the same metallised tape you use to endure a continuous vapour barrier over board joints.

 

I foamed the rear of the boards so hopefully voids were filled by that, and they supported themselves better cut on the rear with the way I propped them

 

I see both sides of the coin, probably for a few remaining tighter bits I will notch the inside of the board, see how it goes 

[ditchcrawler]

17 hours ago, harrybsmith said:

 

I foamed the rear of the boards so hopefully voids were filled by that, and they supported themselves better cut on the rear with the way I propped them

 

I see both sides of the coin, probably for a few remaining tighter bits I will notch the inside of the board, see how it goes 

Would cutting it into narrow, say 3" planks be better on a curved surface.

[nicknorman]

I don’t really see a problem with smallish voids as long as they are sealed to prevent entry of outside air and hence moisture. After all foam is nothing but a large collection of voids!

[Tony Brooks]

1 hour ago, nicknorman said:

I don’t really see a problem with smallish voids as long as they are sealed to prevent entry of outside air and hence moisture. After all foam is nothing but a large collection of voids!

 

I agree, especially if the metal has had some protection applied. Hence, my saying that I think it needs de-rusting and painting, however it seems that it might have been long term greased, so not sure how that will affect the adhesion of paint, foam, or adhesive.

[truckcab79]

2 hours ago, nicknorman said:

I don’t really see a problem with smallish voids as long as they are sealed to prevent entry of outside air and hence moisture. After all foam is nothing but a large collection of voids!

My own limited experience will be that it makes no difference whatsoever.  On our springer project the insulation if you can call it that is a few sheets of loosely inserted polystyrene between 10 and 20mm thick.  Zero rust found to date and it’s well over 40 years old. 

[LeonR]

On 22/11/2023 at 12:45, truckcab79 said:

These chaps are bang on with their suggestions and although I don’t have the curves you are dealing with is how I plan to insulate mine.  Screwfix adhesive foam is decent.  Buy gun foam and a gun, not the disposable cans.  Soudal make a fire rated foam but it’s not ‘fire-proof’ so I wouldn’t bother.  Screwfix expanding foam, gun grade is again good. Don’t buy their guns though.  They’re fine but £25. ToughMaster on Amazon. £15 delivered and better quality.  👍
 

Ignore Kingspan for your Celotex.  Most builders merchants stock an off-brand version at a fraction of the price.  Kingspan 40mm at Wickes is about £37. Lawsons sell basically the same stuff without the logo for almost half. If you can get a trade account even better, though there is no fixed discount, you’ll just get treated better the more you spend and the better your relationship with your account manager.  Mine costs me a £100 bottle of whisky at Christmas. Worth every penny. 👍😂

 

On 22/11/2023 at 12:45, truckcab79 said:

These chaps are bang on with their suggestions and although I don’t have the curves you are dealing with is how I plan to insulate mine.  Screwfix adhesive foam is decent.  Buy gun foam and a gun, not the disposable cans.  Soudal make a fire rated foam but it’s not ‘fire-proof’ so I wouldn’t bother.  Screwfix expanding foam, gun grade is again good. Don’t buy their guns though.  They’re fine but £25. ToughMaster on Amazon. £15 delivered and better quality.  👍
 

Ignore Kingspan for your Celotex.  Most builders merchants stock an off-brand version at a fraction of the price.  Kingspan 40mm at Wickes is about £37. Lawsons sell basically the same stuff without the logo for almost half. If you can get a trade account even better, though there is no fixed discount, you’ll just get treated better the more you spend and the better your relationship with your account manager.  Mine costs me a £100 bottle of whisky at Christmas. Worth every penny. 👍😂

 

@truckcab79 thanks a lot! Loads of good tips there. This forum is amazing. 

[Peanut]

Use a can of gun cleaner, to clear the gun after use, it will stop it getting bunged up.

Edited December 4, 2023 by Peanut
typo

[blackrose]

On 25/11/2023 at 00:33, nicknorman said:

I don’t really see a problem with smallish voids as long as they are sealed to prevent entry of outside air and hence moisture. After all foam is nothing but a large collection of voids!

 

The popular misconception about small voids behind celotex or kingspan is that the steel behind will continue to sweat and cause the steel to rust. However, as you say, as long as any voids are sealed then they will only contain a finite amount of air and a tiny amount of water vapour. Once that's condensed on the steel and potentially caused an imperceptible amount of rust then nothing else can occur. 

[truckcab79]

8 hours ago, Peanut said:

Use a can of gun cleaner, to clear the gun after use, it will stop it getting bunged up.

Definitely don’t do this after each use though. Guns are designed to not be cleaned until the can is emptied and you’re changing one over. They should last a month or so like that, just with the adjustment screw turned down so you can’t pull the trigger. 
 

If you try and clean them between uses you’ll have a clean gun and a gummed up and now expensive but useless can where the little excess has gummed up in the outlet.

 

Give the tip a squirt if you have to but it’s not necessary.  Just let the little bit dry and pick it off when you next need to use it.  The Tough Guard ones as well as being well-priced seem to have a non-stick coating which makes it come off clean every time.  Most of the aluminium or brass ones less so.