WWilts Posted February 21, 2021 Share Posted February 21, 2021 Airtightness required 4.0 Not against doing better, of course. But cost control is a priority. Two storey. Block inner leaf of cavity wall. Initial design is plasterboard on dabs. What materials would you advise to maintain airtightness? Damp-proof membrane seems the front runner. But where exactly in the wall layers? Or what else that is reasonably priced? How would you run services so that it all looked neat? What approach would you take to allow attachment of reasonably heavy stuff to walls in future? Link to comment Share on other sites More sharing options...
ProDave Posted February 21, 2021 Share Posted February 21, 2021 For services, forget dot and dab. Fix an airtight membrane to the wall with 25 by 50mm battens vertically every 400mm. Run all pipes and cables in that service void created by the battens then screw plasterboard to the battens. 2 Link to comment Share on other sites More sharing options...
WWilts Posted February 21, 2021 Author Share Posted February 21, 2021 (edited) 41 minutes ago, ProDave said: Fix an airtight membrane to the wall with 25 by 50mm battens vertically every 400mm. This seems like a way to include internal insulation too. Improving the walls U value. How do folks with internal insulation run services through the void? Would fixing battens over the airtight membrane involve creating airleaks in the membrane? Edited February 21, 2021 by WWilts Link to comment Share on other sites More sharing options...
TonyT Posted February 21, 2021 Share Posted February 21, 2021 What Dave says I used 35mm thick timber as I needed 47mm deep boxes for cooker points and data points. 1 Link to comment Share on other sites More sharing options...
Russell griffiths Posted February 21, 2021 Share Posted February 21, 2021 Improving the airtightness is probably the best bang for your buck. Good details don’t cost much, £5-600 in tape and membranes is a good insurance policy for a better house. 2 Link to comment Share on other sites More sharing options...
WWilts Posted February 21, 2021 Author Share Posted February 21, 2021 Any serious disadvantages to this option for running services in wall? https://youtu.be/jd84Mtt8IlA Link to comment Share on other sites More sharing options...
Russell griffiths Posted February 21, 2021 Share Posted February 21, 2021 8 minutes ago, WWilts said: Any serious disadvantages to this option for running services in wall? https://youtu.be/jd84Mtt8IlA I thought you wanted to improve the airtightness not destroy it. 1 Link to comment Share on other sites More sharing options...
WWilts Posted February 22, 2021 Author Share Posted February 22, 2021 2 hours ago, Russell griffiths said: I thought you wanted to improve the airtightness Alternative approach instead of airtight membrane: Internal airtight layer - Plasterboard with tape to seal joins. Plasterboard is in the equation already Has anyone found plasterboard + tape ok for airtightness? Link to comment Share on other sites More sharing options...
Russell griffiths Posted February 22, 2021 Share Posted February 22, 2021 6 hours ago, WWilts said: Alternative approach instead of airtight membrane: Internal airtight layer - Plasterboard with tape to seal joins. Plasterboard is in the equation already Has anyone found plasterboard + tape ok for airtightness? It works if done correctly, boards have to be fitted with full strips of adhesive, not dabs, all back boxes need fully sealing, any penetrations sealed. Its all about getting the details right. 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted February 22, 2021 Share Posted February 22, 2021 Biggest thing to help would be a wall plate vs cutting the joist ends into the inner leaf of block. Then, a job you can do yourself, is to parge the entire internal face of the inner leaf with a cement slurry mix, applied by brush in most instances, to seal the pores of the block. Chases for cabling are not necessary if you are dabbing boards on, but the boxes will need to be recessed according to final finish depth of boards. If you do have to chase, then they get fully filled back in to maintain airtightness. 3 Link to comment Share on other sites More sharing options...
WWilts Posted February 22, 2021 Author Share Posted February 22, 2021 9 hours ago, Nickfromwales said: wall plate vs cutting the joist ends into the inner leaf of block. Tks. Is that the same as Joist Hangers? Still trying to learn the terms. 9 hours ago, Nickfromwales said: If you do have to chase, then they get fully filled back in to maintain airtightness. Plumbing is main worry. "Fully filled back in". Does that mean plastering to fill in gaps that remain? Apologies for being so ignorant about the terms used. Link to comment Share on other sites More sharing options...
Nickfromwales Posted February 23, 2021 Share Posted February 23, 2021 10 hours ago, WWilts said: Is that the same as Joist Hangers? Still trying to learn the terms. Wall plate is a continuous timber at the ends of the room where the joist ends connect eg instead of cutting into the inner leaf. Joist hangers would be used in conjunction with the wall plates 10 hours ago, WWilts said: Plumbing is main worry Why? Most will be surface mounted and boxed, but can be dabbed over. Usually not as the dab would be quite deep. Same for pipes and cables, chase and bury in strategic places, but cable chases would be back filled with parge and plumbing chases would be foamed to insulate the pipes from their surroundings. 10 hours ago, WWilts said: "Fully filled back in". Does that mean plastering to fill in gaps that remain? Yup. Air will travel through switches and sockets and into the chases. 10 hours ago, WWilts said: Apologies for being so ignorant about the terms used The stupid questions are the ones you didn’t ask. “Apologise yea’ not.” 1 Link to comment Share on other sites More sharing options...
WWilts Posted February 23, 2021 Author Share Posted February 23, 2021 Thanks. Great tips Link to comment Share on other sites More sharing options...
Matt60 Posted February 27, 2021 Share Posted February 27, 2021 On 22/02/2021 at 12:57, Nickfromwales said: Biggest thing to help would be a wall plate vs cutting the joist ends into the inner leaf of block. Then, a job you can do yourself, is to parge the entire internal face of the inner leaf with a cement slurry mix, applied by brush in most instances, to seal the pores of the block. Chases for cabling are not necessary if you are dabbing boards on, but the boxes will need to be recessed according to final finish depth of boards. If you do have to chase, then they get fully filled back in to maintain airtightness. Would this be good to use? Tanking Slurry Waterproof Cement Based Coating 20kg | Builders Merchant Direct (bmdgroup.co.uk) 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted February 28, 2021 Share Posted February 28, 2021 @nod Is there any need to be paying £20 a bag for slurry? Cant this just be a few quid bag-o-cheapo-cement and a bit of additive to DIY mix? Link to comment Share on other sites More sharing options...
nod Posted February 28, 2021 Share Posted February 28, 2021 1 minute ago, Nickfromwales said: @nod Is there any need to be paying £20 a bag for slurry? Cant this just be a few quid bag-o-cheapo-cement and a bit of additive to DIY mix? The Parge coat we often use is more for sound deadening I never call it an airtight coat as it gives the impression that the dry liners don’t need to seal everything So we always call it sound coat So yes any kind of slurry is fine 3-1 stipple with a stiff brush will do the job Save £££ 1 1 Link to comment Share on other sites More sharing options...
Nickfromwales Posted February 28, 2021 Share Posted February 28, 2021 17 hours ago, Matt60 said: Would this be good to use? Tanking Slurry Waterproof Cement Based Coating 20kg | Builders Merchant Direct (bmdgroup.co.uk) 13 minutes ago, nod said: So yes any kind of slurry is fine 3-1 stipple with a stiff brush will do the job Save £££ Bingo. No £20 a bag necessary. 1 Link to comment Share on other sites More sharing options...
nod Posted February 28, 2021 Share Posted February 28, 2021 1 minute ago, Nickfromwales said: Bingo. No £20 a bag necessary. No We do it because it’s on the spec Nearly always housing association 1 Link to comment Share on other sites More sharing options...
ruggers Posted February 22, 2022 Share Posted February 22, 2022 On 23/02/2021 at 08:24, Nickfromwales said: The stupid questions are the ones you didn’t ask. “Apologise yea’ not.” @ProDave @Russell griffiths @Nickfromwales I thought it's much better to jump onto this relatively new post rather than start a new one repeating what many have before. i'm in the final stages of submitting B regs to building control for a masonry build 100mm partial fill cavity house, so if there's any small changes I can make, now is the time. So i have further stupid questions to ask ? I've read a lot of air tightness posts yesterday and theres for and against to all. Theres wet plaster, or parging the inner leaf, then adding a membrane then battens and boards followed by skim finish, or dot & dab with sealed perimeter boards dab with or without parging. Before I heard of sealing the inner wall,I was just going to dnd board to the block having a complete perimeter of dab on each board. Q1. Over 2 floors I have roughly 140m2 of exterior walls that would require parging, how long would this take a professional? Can i brush it on like tanking instead of floating? Q2. What kind of membrane are we using for walls under battens, theres so many? is it duct taped to the ceilign vapour barrier and butyl taped at the bottom to the masonry? Q3. Metal back boxes, i can seal around these with a seal and or board dab, but how do you seal the cables coming into the box? Q4. Do battens/boards/voids not make it even worse for fixing anything to the boards over dnd? Q5. Does a wet plaster finish not make a house lose heat quicker than a plain or insulated board finish when a PIR partial fill cavity is used? I see it too ways, the inner leaf retains the thermal mass via cavity insulation, but boards inside or even better, insulated boards would prevent your heat getting to the inner leaf as quick. Link to comment Share on other sites More sharing options...
JohnMo Posted February 22, 2022 Share Posted February 22, 2022 Anything better than 3 ach may require MVHR are you prepared for that. Q1. Parge coat, two of us (never done it before) approx 210m2 in two days with brushes and on ladders as some walls are 4m tall; that was for Durisol blocks, normal cement blocks will be much easier. 1 Link to comment Share on other sites More sharing options...
ruggers Posted February 23, 2022 Share Posted February 23, 2022 What was your choice or mixture for parge coat, Yes MVHR was planned from the start, Spoken to a few companies and favoured two over the others but would like to do more research on this and not cut corners. Link to comment Share on other sites More sharing options...
JohnMo Posted February 24, 2022 Share Posted February 24, 2022 Parge coat. 25kg cement, 75kg builders sand, 3 shovels hydrated lime. Enough water to give double cream consistency. 1 Link to comment Share on other sites More sharing options...
joe90 Posted February 24, 2022 Share Posted February 24, 2022 I never understood why you need a parge coat if you go wet plaster, I had my builder render inside with cement/sand then wet final coat of plaster, can hang anything from it, really solid (and only parged between floors where plaster not applied.) Link to comment Share on other sites More sharing options...
Nickfromwales Posted February 24, 2022 Share Posted February 24, 2022 27 minutes ago, joe90 said: I never understood why you need a parge coat if you go wet plaster, I had my builder render inside with cement/sand then wet final coat of plaster, can hang anything from it, really solid (and only parged between floors where plaster not applied.) Did you have an AT test? Parge needs to be done before joists / wall plates go in / on, and before floor ( deck ) boards go down, to get to all the areas that are often overlooked. This kind of detailing is why one project just got 3.02 ach and another 0.88. If going for wet coats vs dot n dab then the parge can just be done to get the interior to a point where the plasterer is laying onto just a ribbon of parge and that will be a top job. To achieve air tightness you need to understand all the places which get overlooked and know where to focus your attention. Very easy to get “almost right”, which is basically pointless starting at all. 1 1 Link to comment Share on other sites More sharing options...
JohnMo Posted February 24, 2022 Share Posted February 24, 2022 Try finding a a wet plasterer in NE Scotland, hens teeth, when you do find they are too busy. Plasterboard and Ames taping is the norm around us. So wet plaster was a non starter for us. Link to comment Share on other sites More sharing options...
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