Oz07 Posted December 5, 2019 Share Posted December 5, 2019 I'm stealing @joe90 's method of making the roof airtight except doing it at ceiling level. Going to do whole ceiling with OSB then counter batten with some 2x2 for services All around perimeter where ceiling meets blockwork I will fix 2x2 with 10mm gap as OSB then fill with some foam i've already bought. Supposed to be airtight and elastic - https://www.illbruck.com/en_GB/product/fm330-pro-foam-air-seal/ On all the long joints of the boards i'll be gluing and screwing 2x2 through to the rafters. Short joints also laminated with offcut strips of the OSB. What is best to glue this? Obviously the timber and OSB aren't going to meet perfectly. I could use expanding D4 glue - but is this elastic? Will the seal eventually break? I could use some kind of silicone or sealant if better? What would be recommended? I did think about foam (i've heard people use it to stick skirting) but doesn't it need to have a minimum thickness to be elastic? Cheers Link to comment Share on other sites More sharing options...
joe90 Posted December 5, 2019 Share Posted December 5, 2019 As your knicking my idea ?? I used d4 expanding glue, it’s been there about a year and no sign of deterioration. Tip, I lightly sprayed one surface with water (plant mister) and this makes the glue “bubbly” more. Link to comment Share on other sites More sharing options...
Oz07 Posted December 5, 2019 Author Share Posted December 5, 2019 Cheers I'll copy you entirely then with the sealant choice! 1 Link to comment Share on other sites More sharing options...
nod Posted December 5, 2019 Share Posted December 5, 2019 6 hours ago, Oz07 said: I'm stealing @joe90 's method of making the roof airtight except doing it at ceiling level. Going to do whole ceiling with OSB then counter batten with some 2x2 for services All around perimeter where ceiling meets blockwork I will fix 2x2 with 10mm gap as OSB then fill with some foam i've already bought. Supposed to be airtight and elastic - https://www.illbruck.com/en_GB/product/fm330-pro-foam-air-seal/ On all the long joints of the boards i'll be gluing and screwing 2x2 through to the rafters. Short joints also laminated with offcut strips of the OSB. What is best to glue this? Obviously the timber and OSB aren't going to meet perfectly. I could use expanding D4 glue - but is this elastic? Will the seal eventually break? I could use some kind of silicone or sealant if better? What would be recommended? I did think about foam (i've heard people use it to stick skirting) but doesn't it need to have a minimum thickness to be elastic? Cheers I’m curious why osb Its not airtight Or is it for Something else I do a lot of airtightness and fire protection in my job and normally run a bead of gyproc sealant around the perimeter and use a visqueen membrane across the ceiling leaping down at the edges Then shot fire 25 mil angle around the perimeter trapping the membrane on top of the sealant Link to comment Share on other sites More sharing options...
Oz07 Posted December 6, 2019 Author Share Posted December 6, 2019 Worked for @joe90 good enough for me Link to comment Share on other sites More sharing options...
SteamyTea Posted December 6, 2019 Share Posted December 6, 2019 13 hours ago, Oz07 said: I could use expanding D4 glue - but is this elastic No. 13 hours ago, Oz07 said: Will the seal eventually break Yes 13 hours ago, Oz07 said: I could use some kind of silicone Does not stick to timber that well, it also shrinks over time. 6 hours ago, nod said: Then shot fire 25 mil angle around the perimeter trapping the membrane on top of the sealant This is probably the best, long term, method. Link to comment Share on other sites More sharing options...
nod Posted December 6, 2019 Share Posted December 6, 2019 I’m currently doing a group of fifty that have been stood for ten years It’s the only way we can achieve airtightness due to the outdated design Try and tested over many years Link to comment Share on other sites More sharing options...
ToughButterCup Posted December 6, 2019 Share Posted December 6, 2019 8 hours ago, nod said: I’m curious why osb Its not airtight ... I took the author to mean the gap between the OSB and the 2x2 ...? Link to comment Share on other sites More sharing options...
MikeGrahamT21 Posted December 6, 2019 Share Posted December 6, 2019 FM330 is brilliant stuff! Link to comment Share on other sites More sharing options...
joe90 Posted December 6, 2019 Share Posted December 6, 2019 There was a long thread on another forum about OSB and airtightness, the upshot was ordinary OSB was not completely airtight but it was vapour permeable, some talked about coating the OSB to make it completely airtight, some didn’t. Link to comment Share on other sites More sharing options...
TheMitchells Posted December 6, 2019 Share Posted December 6, 2019 11 hours ago, nod said: Then shot fire 25 mil angle around the perimeter trapping the membrane on top of the sealant please can you translate this into english?? thanks.? Link to comment Share on other sites More sharing options...
Oz07 Posted December 6, 2019 Author Share Posted December 6, 2019 Do we think my 2x2 would better bedded on fm330? Supposed to be elastic just didn't know if it needed a certain thickness to work Link to comment Share on other sites More sharing options...
Oz07 Posted December 6, 2019 Author Share Posted December 6, 2019 4 hours ago, AnonymousBosch said: I took the author to mean the gap between the OSB and the 2x2 ...? He's saying why use osb. I'm thinking if it's good enough for @joe90 it's good enough for me I'm not trying to beat the world 1 Link to comment Share on other sites More sharing options...
joe90 Posted December 6, 2019 Share Posted December 6, 2019 2 hours ago, TheMitchells said: please can you translate this into english?? thanks.? Nail gun!!! Link to comment Share on other sites More sharing options...
nod Posted December 6, 2019 Share Posted December 6, 2019 1 hour ago, Oz07 said: He's saying why use osb. I'm thinking if it's good enough for @joe90 it's good enough for me I'm not trying to beat the world Just trying to help OSB isn’t airtight You could put a membrane in at a fraction of the the cost and time Link to comment Share on other sites More sharing options...
joe90 Posted December 6, 2019 Share Posted December 6, 2019 11 minutes ago, nod said: You could put a membrane in at a fraction of the the cost and time You will need tape etc to seal it up and that’s not cheap. Personally I don’t like membranes and sticky tape even less. As per above, I know OSB is not airtight (unless you coat/paint it) but my airtest was pretty good. I also liked the OSB to give racking strength to the roof. Link to comment Share on other sites More sharing options...
Oz07 Posted December 6, 2019 Author Share Posted December 6, 2019 18 minutes ago, nod said: Just trying to help OSB isn’t airtight You could put a membrane in at a fraction of the the cost and time Appreciated nod what are u paying for the membrane? I prices it up the osb is near on 3 quid a m2. By the time you buy membrane and tape was coming out more expensive and I think fiddly/harder to Do. Like I say not trying to achieve and super performance just enough to make the mvhr worthwhile 1 Link to comment Share on other sites More sharing options...
joe90 Posted December 6, 2019 Share Posted December 6, 2019 @Oz07 if you want to make the OSB completely airtight just paint it with a non breathable paint ?. Link to comment Share on other sites More sharing options...
SteamyTea Posted December 7, 2019 Share Posted December 7, 2019 21 hours ago, joe90 said: make the OSB completely airtight just paint it with a non breathable paint Would it not take several coats as OSB is not exactly flat and easy to paint. Link to comment Share on other sites More sharing options...
Triassic Posted December 8, 2019 Share Posted December 8, 2019 You can buy airtight OSB, no doubt it’ll be a premium product with a price to match Link to comment Share on other sites More sharing options...
joe90 Posted December 8, 2019 Share Posted December 8, 2019 On 07/12/2019 at 12:55, SteamyTea said: Would it not take several coats as OSB is not exactly flat and easy to paint. A rubberised paint springs to mind. Link to comment Share on other sites More sharing options...
willbish Posted December 8, 2019 Share Posted December 8, 2019 On 06/12/2019 at 09:19, MikeGrahamT21 said: FM330 is brilliant stuff! How much better is FM330 compared to a similar gun grade low ex foam for airtightness? Is it correct to assume that other foams are just as air tight but the FM330 has the flexibility so will stay airtight over a longer period. Comparing the datasheets for different brands isn't much help as they don't have common parameters Link to comment Share on other sites More sharing options...
MikeGrahamT21 Posted December 9, 2019 Share Posted December 9, 2019 10 hours ago, willbish said: How much better is FM330 compared to a similar gun grade low ex foam for airtightness? Is it correct to assume that other foams are just as air tight but the FM330 has the flexibility so will stay airtight over a longer period. Comparing the datasheets for different brands isn't much help as they don't have common parameters Its like a totally different product compared with normal low expansion foam, doesn't set completely hard, and remains very flexible with a high bond strength to the substrates. You discover just how strong when you try and remove it from somewhere you didn't want it to be. Normal expansion foam isn't airtight, and you tend to get a micro crack in the bond at some point. Link to comment Share on other sites More sharing options...
willbish Posted December 9, 2019 Share Posted December 9, 2019 Thanks @MikeGrahamT21 I shall give it a try, I've got a few tricky places where a new air tight build meets an old party wall. The only other foam I can find that claims EN12114 air tightness is Everbuild Thermofoam , which is slightly cheaper, do you have any experience with this? Link to comment Share on other sites More sharing options...
Gone West Posted December 9, 2019 Share Posted December 9, 2019 I used Soudal Flexifoam which claims to be airtight. Air permeability (DIN 18542) a < 0,1 m³/[h.m.(daPa)²/³] Link to comment Share on other sites More sharing options...
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