Fiat Ducato Posted March 4, 2016 Share Posted March 4, 2016 Hi Everyone Just thought I'd share this with you all and would love to here your views on this topic. I recently contacted Celotex Technical Department to ask them which adhesive they would recommend to use to bond 20 mm Celotex sheets to the Aluminium skin of my Coach built Motorhome after it suffered water ingress damage and basically 1/3 of the interior need to ripped out and rebuilt, all new timbers in roof, back wall and half of side wall. I received this email back "Unfortunately Celotex is not recommend for use in this type of construction due to the increased risk of condensation when insulating hard against an impermeable material such as aluminium. A ventilated cavity is required between the Celotex and the aluminium in order to remove any warm moisture air that may work its way through the insulation layer itself" I found this strange as the original insulation installed in the van during it's original construction was just 20 mm polystyrene. So my way of thinking was surely 20 mm Celotex would be a much better option then the white polystyrene, as polystyrene is highly flammable and doesn't have no where near the same R value as Celotex plus Celotex or similar as the foil barrier on both sides which itself acts as a vapour barrier. Also many of the major Motorhome Coach Building companies now use Styrofoam bonded in a sandwich type contruction in their motorhomes now, and not sure what the difference is between Styrofoam and PIR insulation, Obviously StyroFoam is Extruded Polystyrene and Celotex is Rigid Polyurethane insulation. Anyways I replied to this Rob Firman from Celotex saying the above and then got another email from him saying this: "Dear Paul Thank you for your email and my apologies in our delay in responding to you previously. We would generally advise against insulating to the inside of materials such as aluminium as they offer a very high vapour resistance. Under normal circumstances we would recommend a ventilated cavity between the insulation and the aluminium similar to a cladding build-up that our products would commonly be used in. However, your particular use of the boards is untested by Celotex so we would be unable to confirm the suitability. It may be that companies such as Adria or AutoSleeper have tested this type of system and assessed the risk of condensation in more depth. We would however recommend maintaining a continuous vapour control layer to the warm side of the insulation in all construction build-ups in order to minimise the risk of harmful condensation. Unfortunately it is not recommend to adhere foil faced boards however if you chose to do so a PU type of adhesive would give you the best chance of success. Finally, the differences between an expanded polystyrene type of insulation and a foil faced PIR insulation such as Celotex is that expanded polystyrene insulations have a lower vapour resistance compared with a PIR insulation. The PIR style insulations would however be much more thermally efficient. I hope this is of assistance. Kind regards Rob Firman Technical Services Officer" All very interesting, please post your comments and thoughts on this matter by all means, love to here others opinions on this. Regards Paul Link to comment Share on other sites More sharing options...
colin Posted March 4, 2016 Share Posted March 4, 2016 AFAik Celotex PIR is not a true closed cell foam like Styrofoam. Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 4, 2016 Share Posted March 4, 2016 They are right to be cautious. The external aluminium skin of the vehicle acts as a vapour barrier. A vapour barrier should always be on the warm side of the insulation to prevent the warm moisture laden air condensing on the cold outer layer, or even within the insulation itself. The alternative is to use a closed cell insulant so that the water vapour cannot pass through it to condense. In reality, even a closed cell product such as Styrofoam will pass some water vapour (as will the little gaps where the foam abuts the frames, but generally not sufficient to cause problems. Sounds as though you've been making good progress on your rebuild if you've reached that stage. How about some pics? Link to comment Share on other sites More sharing options...
Derek Uzzell Posted March 5, 2016 Share Posted March 5, 2016 Paul Celotex PIR is aimed at insulating buildings and there is no suggestion that the material is suitable for insulating leisure-vehicles http://www.celotex.co.uk/applications Celotex have recommended against what you were planning to do, but have said that a PU type of adhesive would give you the best chance of success if you decided to ignore that recommendation. It’s your choice... Link to comment Share on other sites More sharing options...
Muswell Posted March 5, 2016 Share Posted March 5, 2016 Something else I would think about is the thermal expansion of the aluminium. I have some polystyrene and some PIR insulation and the IR is more rigid and rather friable than the polystyrene. I would be concerned that temperature cycling might cause the interface to break down if PIR were used. Link to comment Share on other sites More sharing options...
aandncaravan Posted March 5, 2016 Share Posted March 5, 2016 As you probably know by now we restore Citroen H vans (maybe you saw the one we did for the Wheeler Dealers TV show?) and most of these vehicles are adapted to Catering vehicles where cooking 12 hours a day produces a lot of condensation. We are seeing vans rusted from the inside out because of excess moisture condensing on the cold Steel walls behind the panelling/insulation. What we have been advised to do is seal the metal surface to protect it should it get wet, ideally with a thick layer that also acts as an insulator. The idea being that if the substance is thick enough the amount of water that condenses out will be reduced as well as the surface protected. We now epoxy prime the inside of the van and then put on a thick layer of Stone chip. Don't know if this will help but the stonechip panel does feel a lot 'warmer' than an unpainted panel. I am guessing that the suggested adhesive above will both seal the surface, so inhibiting corrosion, and provide some 'insulation' at the panel itself so reducing condensation? Therefore liberal use of this stuff and Celotex might work well? Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 5, 2016 Share Posted March 5, 2016 Not much Allan. One needs to stop the moisture getting into the insulant, not stop it getting out. Warm, moist, air is generated inside the van. There is a temperature gradient through the thickness of the insulant. Inside surface at roughly the air temperature in the van, outside surface at the temperature of the outer skin of the van. As that warm moist,air passes into the insulant it will be cooled in line with the temperature gradient. If, in that gradient, the air is cooled below its dew point, the moisture will condense out. Usually, this will be somewhere near the outside surface of the insulant, possibly at the external skin, which will in any case not allow the trapped moisture out. With a more extreme temperature gradient, say negative figures outside, the point at which the air reached dew point will move towards the interior of the van, and the condensation will take place within the insulant. Insulants that are vapour permeable will therefore become saturated from that point out, reducing their insulating properties, and exacerbating the problem. So, either use a closed cell insulant, where the moisture vapour doesn't penetrate the insulant, or apply a vapour barrier to the inside of the insulant, behind the wallboard lining. Vapour barriers of this type need to have all joints taped over so that the water vapour is as fully excluded as possible. Link to comment Share on other sites More sharing options...
Fiat Ducato Posted March 5, 2016 Author Share Posted March 5, 2016 Ho thank you all for your comments and very interesting to hear all your opinions regarding this matter. To be honest with you all I am well and truly gutted as in my line of work I have used celotex many many times before in properties and lofts, roofs, flat roofs etc. And always rated it very high as a insulation. I then transferred this knowledge to using it on my motorhome thinking it would be an excellent insulation like in buildings. Obviously I was MISTAKEN and to make things worst I contacted Celotex about a month ago several times and never heard back. I then tried phoning them several times over the past 2 weeks with no answer, emailed them twice and finally couldn't wait any longer as needed to press on with the installing the insulation as the weather is now getting better, more sunnier days to work. I did research Styrofoam and although it is a little more expensive than Celotex, money wasn't the factor in deciding against buying it. I was convinced that celotex would be a better option. So I went ahead and purchased 3 sheets of 20mm Celotex to be delivered as had to be specially ordered in. And not hanging around I had already done the majority of fitting the insulation in the van when Celotex got back to be with this bad news. I have cut them nice and tight into the spaces between the timbers and boned them to the aluminium skin with Everbuild Puraflex PU40, so they are now not going anywhere, also compressed them to the skin to replicate the sandwich design which was used originally. Been somewhat of a perfectionist and want to do this renovation/repairs to highest spec I can possibly do. I am considering now ripping the celotex all out and starting again with the blue Styrofoam. Not to bothered about the wasted £50 or so cost but more concerned about the damage I will cause when I come to remove the bonded Celotex. I am fairly sure it will pull off, all the fibreglass repairs I did covering the holes from the inside and filled with body filler on the outside. as well as bending and distorting the outer skin. I have also installed it in my roof 25mm Celotex but thats is fitted in a slightly different way, 5/6mm exxterior plywood against the outer roof skin, the timbers bonded and screwed into place, then the celotex bonded to the plywood in between the spaces, then there will be another layer of 5/6mm exterior plywood and finally a layer of waterproof self adhesive paper. This job as been one disaster from start, from what seem to be water ingress damage confined to a small area once I started ripping out and uncovering, turned out to be the entire roof from front to back, the complete back wall, all rotten timbers soaking wet. And half of the side wall where the bathroom was situated. I removed everything, the complete bathroom taken out, wooden partitions taken out, rear window taken out, seats and cupboards on one side gone, bought 2 new larger better design skylights, all new LED downlights fitted on 3 separate circuits for above cab, above central seating area and for rear. Bought new vents for bathroom and truma vent for heater flue. Removed the full length of corner aluminium extrusion which proved to be a complete nightmare as all the screws were completely rusted, bent and twisted the extrusion removing it, so had to order two new 3m lengths from Trigano in Italy. Cleaned and resealed the entire length of the van, then did the other side. New stainless steel screws, new pvc Herzim strip fitted in all extrusions. What a hell of a job, surely been one learning curve and if I ever were to tackle something on this magnitude ever again, there is quite a few things I would differently next time. Like not doing it all by yourself lol. Not doing outside under a tarpaulin sheet, and most importantly I wouldn't bother farting around with all the poxy rotted pin holes in the aluminium skin, treating them, then filling them. Would just replace the Aluminium skin for new sheet. Hey oh life is one big learning curve. Paul Link to comment Share on other sites More sharing options...
Fiat Ducato Posted March 5, 2016 Author Share Posted March 5, 2016 Brian Kirby - 2016-03-05 11:42 AM Not much Allan. One needs to stop the moisture getting into the insulant, not stop it getting out. Warm, moist, air is generated inside the van. There is a temperature gradient through the thickness of the insulant. Inside surface at roughly the air temperature in the van, outside surface at the temperature of the outer skin of the van. As that warm moist,air passes into the insulant it will be cooled in line with the temperature gradient. If, in that gradient, the air is cooled below its dew point, the moisture will condense out. Usually, this will be somewhere near the outside surface of the insulant, possibly at the external skin, which will in any case not allow the trapped moisture out. With a more extreme temperature gradient, say negative figures outside, the point at which the air reached dew point will move towards the interior of the van, and the condensation will take place within the insulant. Insulants that are vapour permeable will therefore become saturated from that point out, reducing their insulating properties, and exacerbating the problem. So, either use a closed cell insulant, where the moisture vapour doesn't penetrate the insulant, or apply a vapour barrier to the inside of the insulant, behind the wallboard lining. Vapour barriers of this type need to have all joints taped over so that the water vapour is as fully excluded as possible. Hello Brian I appreciate what your saying about the condensation problems, but Celotex is quoted as been water impermeable and along with the foil layer on both sides which itself is water proof (as long as its not punctured), can't see how this would cause a problem, as long as I'm extremely careful not to have any thermal/cold bridges anywhere. Also the warm heat from the inside of the van would need to travel through the waterprrof lining paper, through the 5/6 exterior plywood, through the 20mm Celotex to reach the cold surface of the Aluminium outer skin. Is that possible? This was my way of thinking when I planned to use Celotex. Paul Link to comment Share on other sites More sharing options...
Fiat Ducato Posted March 5, 2016 Author Share Posted March 5, 2016 Brian Kirby - 2016-03-05 11:42 AM Not much Allan. One needs to stop the moisture getting into the insulant, not stop it getting out. Warm, moist, air is generated inside the van. There is a temperature gradient through the thickness of the insulant. Inside surface at roughly the air temperature in the van, outside surface at the temperature of the outer skin of the van. As that warm moist,air passes into the insulant it will be cooled in line with the temperature gradient. If, in that gradient, the air is cooled below its dew point, the moisture will condense out. Usually, this will be somewhere near the outside surface of the insulant, possibly at the external skin, which will in any case not allow the trapped moisture out. With a more extreme temperature gradient, say negative figures outside, the point at which the air reached dew point will move towards the interior of the van, and the condensation will take place within the insulant. Insulants that are vapour permeable will therefore become saturated from that point out, reducing their insulating properties, and exacerbating the problem. So, either use a closed cell insulant, where the moisture vapour doesn't penetrate the insulant, or apply a vapour barrier to the inside of the insulant, behind the wallboard lining. Vapour barriers of this type need to have all joints taped over so that the water vapour is as fully excluded as possible. Hello Brian I appreciate what your saying about the condensation problems, but Celotex is quoted as been water impermeable and along with the foil layer on both sides which itself is water proof (as long as its not punctured), can't see how this would cause a problem, as long as I'm extremely careful not to have any thermal/cold bridges anywhere. Also the warm heat from the inside of the van would need to travel through the waterprrof lining paper, through the 5/6 exterior plywood, through the 20mm Celotex to reach the cold surface of the Aluminium outer skin. Is that possible? This was my way of thinking when I planned to use Celotex. Paul Link to comment Share on other sites More sharing options...
colin Posted March 5, 2016 Share Posted March 5, 2016 When I've used Celotex in buildings it has always had a vapour control barrier on the inside and a breatherble outer layer. Link to comment Share on other sites More sharing options...
goldi Posted March 5, 2016 Share Posted March 5, 2016 Good afternoon , I reckon you are overthinking and worrying about what you have done, it sounds as good as anything to me. norm Link to comment Share on other sites More sharing options...
snowie Posted March 5, 2016 Share Posted March 5, 2016 Hi Paul; the outer aluminium skin is the weatherproof, rainproof membrane, and the inside face of it is where you will risk condensation forming, because it will be cold, in winter, (warm/hot in summer). What you need to do is prevent moisture laden air pass into and through the inner, facing material and insulation. So you need a continuous vapour barrier on the inside face of the insulation. Sealing joints in this vapour barrier is the important bit. If I were insulating a bespoke van, or specifying it I would be tempted to use Celotex, and I would use foil tape over the gaps between boards, and around the edges of the boards. I might even try to incorporate some ventilation from the outer face of the insulation; but then maybe that would be over-thinking it? Whatever I did would be my responsibility and mine alone. I would live with that. Good luck alan b p.s. The washroom is your most "dangerous" area I think, take care, do it well. Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 5, 2016 Share Posted March 5, 2016 Fiat Ducato - 2016-03-05 12:36 PM.........................................Hello Brian I appreciate what your saying about the condensation problems, but Celotex is quoted as been water impermeable and along with the foil layer on both sides which itself is water proof (as long as its not punctured), can't see how this would cause a problem, as long as I'm extremely careful not to have any thermal/cold bridges anywhere. Also the warm heat from the inside of the van would need to travel through the waterprrof lining paper, through the 5/6 exterior plywood, through the 20mm Celotex to reach the cold surface of the Aluminium outer skin. Is that possible? This was my way of thinking when I planned to use Celotex. Paul Then, I'd leave the Celotex in place rather than pull it all out. The foil face will give it the vapour barrier it needs. As I said, either impermeable insulant, or a vapour barrier (or both for belt and braces). I believe you can get a sealing tape designed to cover the joints between Celotex sheets. Apply that across the timber frames so that it laps onto the Celotex on both sides of the frames. That way, you'll keep the water vapour out of the timber as well, while protecting the cut edges of the Celotex from vapour penetration. Also, patch any perforations of the inner foil face with the tape. It'll be a significantly better job than was done originally! The problem is not waterproofing, it is water vapour proofing. The vapour is invisible, and has a very small molecule and consequently penetrates most materials. Houses breathe on the outside, through their walls, and through their roofs (unless metal clad, asphalted, or felted). So, generally, the vapour just escapes. Motorhomes have the most perfect vapour barrier on the outside, which is not where one wants it. The only way to prevent interstitial condensation then, is to keep the vapour out of the insulation. The foil face on the Celotex is an excellent vapour barrier, it just needs to be continued across all frames etc. Then, with the internal wallboard applied over the lot, you will have protected the barrier from damage and it should perform extremely well, and go on doing so indefinitely. Keep what you've done, get some of the tape, apply it, and continue to make progress. It'll be fine. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted March 6, 2016 Share Posted March 6, 2016 goldi - 2016-03-05 4:57 PM Good afternoon , I reckon you are overthinking and worrying about what you have done, it sounds as good as anything to me. norm I wholeheartedly agree... The vehicle being repaired is a 1997-vintage Auto-Roller motorhome not a Ferrari GTO. The construction methodology Paul has adopted will be at least equal (and probably superior) to that used when the motorhome was originally built and - although Celotex PIR might, on paper, not be the ideal roof insulant for a motorhome - it should do the job perfectly well. I’m also afflicted with ‘perfectionism’ and it needs to be kept under tight control. I find that a regular dose of realism helps, combined with not asking for advice. ;-) ;-) Link to comment Share on other sites More sharing options...
Mike88 Posted March 6, 2016 Share Posted March 6, 2016 Why not use thinsulate? Link to comment Share on other sites More sharing options...
Brian Kirby Posted March 6, 2016 Share Posted March 6, 2016 Mike88 - 2016-03-06 10:46 AM Why not use thinsulate? Because a) the Celotex is already fitted, and b) Thinsulate is an inferior product, the performance claims for which were shown to be exaggerated when subjected to industry standard testing. Link to comment Share on other sites More sharing options...
aandncaravan Posted March 6, 2016 Share Posted March 6, 2016 From the description of how you have planned and carried out the work, I think you have done good. I therefore stand by our last paragraph that this will work well. As Derek, says way better than original. Link to comment Share on other sites More sharing options...
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