Moggaman Posted December 14, 2020 Share Posted December 14, 2020 Hi all I think i am settled on a 200mm wide masonry cavity with pumped in beads and a sand cement skim render on the inside for airtightness. What happens tho when you in and want to hang tvs , pictures etc ,, you will be puncturing the layer. Assuming you are using drilled holes into blockwork with rawl plugs, they could be a weak point,,,several weak points? Thanks Link to comment Share on other sites More sharing options...
Onoff Posted December 15, 2020 Share Posted December 15, 2020 Silicone in the fixing holes? Link to comment Share on other sites More sharing options...
Onoff Posted December 15, 2020 Share Posted December 15, 2020 Don't forget about making your back boxes airtight! 1 Link to comment Share on other sites More sharing options...
tonyshouse Posted December 15, 2020 Share Posted December 15, 2020 Much more relevant problems with sealing to adjoining air barriers, all round windows, penetrations and joist/beam ends 1 Link to comment Share on other sites More sharing options...
Oz07 Posted December 15, 2020 Share Posted December 15, 2020 Osb to jambs and heads foamed on with that illbruck airtight foam against the cav closers. Boards direct screwed to the osb afterwards. Same method with window board Link to comment Share on other sites More sharing options...
Moggaman Posted December 15, 2020 Author Share Posted December 15, 2020 3 hours ago, tonyshouse said: Much more relevant problems with sealing to adjoining air barriers, all round windows, penetrations and joist/beam ends Plaster will lap the airtightness tape at windows .?. That should do it? Link to comment Share on other sites More sharing options...
PeterW Posted December 15, 2020 Share Posted December 15, 2020 Why go sand and cement and then board and plaster ..? Why not use bonding then multi finish and you’ll take out cost and materials. Holes for TVs etc are negligible - you need to watch for details at floors , joists and ceilings as @tonyshouse says. 1 Link to comment Share on other sites More sharing options...
Moggaman Posted December 15, 2020 Author Share Posted December 15, 2020 4 hours ago, PeterW said: Why go sand and cement and then board and plaster ..? Why not use bonding then multi finish and you’ll take out cost and materials. Holes for TVs etc are negligible - you need to watch for details at floors , joists and ceilings as @tonyshouse says. Thanks, yes that’s what I meant. There will be no plasterboard on the inside Link to comment Share on other sites More sharing options...
Mr Punter Posted December 15, 2020 Share Posted December 15, 2020 How do you fit windows with a wide cavity? I wouldn't want to sit them on a cavity closer over a 200mm void. Link to comment Share on other sites More sharing options...
Oz07 Posted December 15, 2020 Share Posted December 15, 2020 I honestly wouldn't waste the effort thinking about this issue with fixings. I've pargecoated and direct fixed into the block with screws. I've also nailed/screwed thru airtight membrane to ceiling. The fixing traps the hole. I scored just over 1 on air test. 2 Link to comment Share on other sites More sharing options...
Moggaman Posted December 15, 2020 Author Share Posted December 15, 2020 5 hours ago, Mr Punter said: How do you fit windows with a wide cavity? I wouldn't want to sit them on a cavity closer over a 200mm void. Fitted in line with the insulation to create thermal continuity. Fixed by straps to the blocks either side? Link to comment Share on other sites More sharing options...
tanneja Posted January 16, 2021 Share Posted January 16, 2021 What is the most effective and cost effective 5mm process to the external blockwork to attempt an airtight later out of a parge coat (or parge plus), vs a layer of bonding (the stuff is super sticky, surely it is air tight). I think the builder would rather dot and dab over either approach. Link to comment Share on other sites More sharing options...
joe90 Posted January 16, 2021 Share Posted January 16, 2021 1 hour ago, tanneja said: I think the builder would rather dot and dab over either approach. Mine wanted to but I said no, sand cement parge/first coat then multi finish coat. Yes it’s windows, doors roof that is the biggest challenge re airtightness rather than the odd fixing. 1 Link to comment Share on other sites More sharing options...
Iceverge Posted January 17, 2021 Share Posted January 17, 2021 0.31 ACH 50 with sand cement plaster here. On my preliminary testing with my DIY fan all the leaks were around the windows, doors, wall to ceiling junction, and back boxes where the electric drilled. These were quickly fixed with airtight sealant and tape. 1 1 Link to comment Share on other sites More sharing options...
tanneja Posted January 17, 2021 Share Posted January 17, 2021 2 hours ago, Iceverge said: 0.31 ACH 50 with sand cement plaster here. On my preliminary testing with my DIY fan all the leaks were around the windows, doors, wall to ceiling junction, and back boxes where the electric drilled. These were quickly fixed with airtight sealant and tape. @Iceverge what was your strategy with the back boxes? Im torn between putty pads or airtight paint. I dont want to materially reduce the available internal depth of my backboxes as plan for zwave modules to permit automations. Not bought a putty pad yet to see how bulky it is. Link to comment Share on other sites More sharing options...
TonyT Posted January 17, 2021 Share Posted January 17, 2021 Wrap the box externally with tescon tape or similar then fix to wall will be cheaper. lets assume 1 knock out with a gromett and 2 fixing screw then to get a dab of silicone over to completely seal them Link to comment Share on other sites More sharing options...
Iceverge Posted January 17, 2021 Share Posted January 17, 2021 1 hour ago, tanneja said: @Iceverge what was your strategy with the back boxes? Im torn between putty pads or airtight paint. I dont want to materially reduce the available internal depth of my backboxes as plan for zwave modules to permit automations. Not bought a putty pad yet to see how bulky it is. Airtight paint (belgacoat) in the chases and in the cut out for the boxes, wet plastered over everything afterwards. Airtight sealant for any pin holes detected later on as it was quicker for spot filling. I found priming the surfaces beforehand with a dilute solution of airtight paint improved adhesion and saved a lot of paint. Wrapping the back box isn't as robust a strategy in my opinion and it relies on the electrician. Link to comment Share on other sites More sharing options...
TonyT Posted January 17, 2021 Share Posted January 17, 2021 No you wrap the metal boxes then hand them over to the electrician to fit as normal it then only leaves the cable entry hole and 2 fixing holes. 1 Link to comment Share on other sites More sharing options...
Iceverge Posted January 17, 2021 Share Posted January 17, 2021 How 4 minutes ago, TonyT said: No you wrap the metal boxes then hand them over to the electrician to fit as normal it then only leaves the cable entry hole and 2 fixing holes. I'm interested to know how this works. How do you stop air escaping from the chase at the back of the conduit? It can leak from the top or the conduit downwards along the exposed blockwork at the back of the chase that the wet plaster won't reach? What kind of blower door results have you had using it? Link to comment Share on other sites More sharing options...
joe90 Posted January 17, 2021 Share Posted January 17, 2021 2 minutes ago, Iceverge said: How do you stop air escaping from the chase at the back of the conduit? It can leak from the top or the conduit downwards along the exposed blockwork at the back of the chase that the wet plaster won't reach? Silicone or similar both ends of the chase Link to comment Share on other sites More sharing options...
TonyT Posted January 17, 2021 Share Posted January 17, 2021 Joe90’s got it Link to comment Share on other sites More sharing options...
Iceverge Posted January 17, 2021 Share Posted January 17, 2021 2 minutes ago, joe90 said: Silicone or similar both ends of the chase Before or after plastering? Link to comment Share on other sites More sharing options...
TonyT Posted January 17, 2021 Share Posted January 17, 2021 You aren’t going to get the top after plastering, that has to be done after cables are pulled in. Link to comment Share on other sites More sharing options...
Ronan 1 Posted January 17, 2021 Share Posted January 17, 2021 14 minutes ago, joe90 said: Silicone or similar both ends of the chase Is it silicone in either end of the conduit ?? Sorry if that sounds stupid. Is it the air coming down through the conduit that the cables are in and out through the socket boxes?? Link to comment Share on other sites More sharing options...
Iceverge Posted January 17, 2021 Share Posted January 17, 2021 7 minutes ago, TonyT said: You aren’t going to get the top after plastering, that has to be done after cables are pulled in. My fear is that the silicon would be dislodged by the plasterers and electrician. We kept all the wiring inside the airtight envelope so air in the conduits itself wasn't an issue. My worry was the blockwork behind the conduit. Link to comment Share on other sites More sharing options...
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