ToughButterCup Posted September 13, 2017 Share Posted September 13, 2017 That's the thing about building a house; there are too many choices. And I'm at the bottom of yet another really steep learning curve. Hence this post. We need to render the internal space between the ceiling and first floor to make sure this area is airtight before we fit the POSIs. At this stage in our decision making process, I usually turn to the online version of SPONS and look at what's available. Comprehensive though the section on rendering is, there's no mention of rendering to provide simple air-tightness. For this small section, the look of the render and surface finish is irrelevant, and thickness is only important in so far as air-tightness is concerned. Waterproofing isn't relevant. I've come to understand that this process, however humble it may be, is key to keeping our future living cost down. So it's important to get it right. Could you just give me some starters to help me widen my research, please? So far I have Looked through SPONS for trade names and researched those that I found : Tyrolean Finish, Cement and sand, SIKA waterproof render, Sto External render, Armat Classic Basecoat, K-Rend. Done an internet search and come up with this interesting article: maybe we should simply render over an airtight membrane. Visited the GBF and read this article, but it's mainly about air-tightness tapes: it raises important issues though about finding plasterers who are keen on attention to detail. Knotty one that. Found out that there's stuff called undercoat plaster......... This hill is steeper than I thought. Ian Link to comment Share on other sites More sharing options...
PeterW Posted September 13, 2017 Share Posted September 13, 2017 Sand and cement will do it, smeared on with a hessian sack. 1 Link to comment Share on other sites More sharing options...
gravelld Posted September 13, 2017 Share Posted September 13, 2017 Is there a section in SPONS about AT? That's where I'd expect it to be. I find it incredibly frustrating this kind of best practice info isn't easily available. AFAIK, S+C does the job over most of the wall, then tape onto penetrations like joists. Can't say I'm overly keen on S+C lasting a long time, in which case you could use a membrane e.g. Intello. Link to comment Share on other sites More sharing options...
ProDave Posted September 13, 2017 Share Posted September 13, 2017 The only thing I can add to this, if using a membrane, is Protect Barriair is a lot cheaper than Intello. Link to comment Share on other sites More sharing options...
ToughButterCup Posted September 13, 2017 Author Share Posted September 13, 2017 30 minutes ago, PeterW said: Sand and cement will do it, smeared on with a hessian sack. I knew the answer would be high tech. 6 minutes ago, gravelld said: Is there a section in SPONS about AT? That's where I'd expect it to be. I find it incredibly frustrating this kind of best practice info isn't easily available. AFAIK, S+C does the job over most of the wall, then tape onto penetrations like joists. Can't say I'm overly keen on S+C lasting a long time, in which case you could use a membrane e.g. Intello. AT means...? S+C means sand and cement doesn't it? Both @ProDave and @gravelld have mentioned using a membrane (Intello or Protect Barriair) Why use one when sand and cement might be all we need ? What does a 'long time mean'? Years, weeks, a generation? Link to comment Share on other sites More sharing options...
PeterW Posted September 13, 2017 Share Posted September 13, 2017 Sand and cement will cover the pores. Seal around your joists with expanding foam then tape over that. Put your ceiling noggins in around the edge and tape that joint to the wall - when you put your ceiling and wall boards on then nothing is getting into that gap .... Link to comment Share on other sites More sharing options...
Dudda Posted September 13, 2017 Share Posted September 13, 2017 I know it's a refurb job in my case but the same principles apply. Step 1 is tape around any joints or joists. Step 2 is use a very wet sand and cement mix and apply like it's a very thick paint with a sweeping brush or similar. It can be messy as it's wet and can go everywhere. It will only be 2-3 mm thick but that's all it needs to be. Link to comment Share on other sites More sharing options...
ToughButterCup Posted September 13, 2017 Author Share Posted September 13, 2017 Just what an fella needs @Dudda ! Thanks. Link to comment Share on other sites More sharing options...
ToughButterCup Posted September 13, 2017 Author Share Posted September 13, 2017 OK folks next step... I've been told that I need to make sure that the wall must be as flat as I can get it (where it butts up to the floor boards) so that when they come to fit the flooring, the fit will be really flush. Hmmm. It looks as if the workflow can be; Fit the joists (POSIs) Tape round the edges, Sloppy sand and cement wash over the area Fit the floor boards Link to comment Share on other sites More sharing options...
MikeSharp01 Posted September 13, 2017 Share Posted September 13, 2017 27 minutes ago, recoveringacademic said: AT means...? Air Tightness. Link to comment Share on other sites More sharing options...
Dudda Posted September 13, 2017 Share Posted September 13, 2017 10 minutes ago, recoveringacademic said: OK folks next step... I've been told that I need to make sure that the wall must be as flat as I can get it (where it butts up to the floor boards) so that when they come to fit the flooring, the fit will be really flush. Hmmm. It looks as if the workflow can be; Fit the joists (POSIs) Tape round the edges, Sloppy sand and cement wash over the area Fit the floor boards That's right. The last step I'd suggest is putting in some acoustic mastic sealant (or similar - could be tape) between the floorboards and the wall. The timber floor will expand and contract at different rates to the blockwork and (presuming these are first floor joists) you'll want to keep the noise transfer down. While the gap might be covered by skirting to correct it visually it's not a great seal for reducing noise transfer. You don't want to hear a TV downstairs when trying to sleep. Link to comment Share on other sites More sharing options...
MikeSharp01 Posted September 13, 2017 Share Posted September 13, 2017 It seems to me that the only challenge to the sand and cement scenario is the likelihood of cracking if there is any movement / flex so anywhere it might move / flex, like round the ends of joists (differential expansion / contraction) use a membrane and tape to ensure cracking does not harm the air tightness. Link to comment Share on other sites More sharing options...
gravelld Posted September 13, 2017 Share Posted September 13, 2017 3 minutes ago, MikeSharp01 said: It seems to me that the only challenge to the sand and cement scenario is the likelihood of cracking if there is any movement / flex so anywhere it might move / flex, like round the ends of joists (differential expansion / contraction) use a membrane and tape to ensure cracking does not harm the air tightness. This. Link to comment Share on other sites More sharing options...
ToughButterCup Posted September 13, 2017 Author Share Posted September 13, 2017 28 minutes ago, MikeSharp01 said: [...] so anywhere it might move / flex, like round the ends of joists (differential expansion / contraction) use a membrane and tape to ensure cracking does not harm the air tightness. Trade names for membrane and tape please. Thanks Ian Link to comment Share on other sites More sharing options...
ProDave Posted September 13, 2017 Share Posted September 13, 2017 Why do they want the floor boards to be a tight fit up to the wall? what about a small expansion gap? Skirting board will cover any gap so why wanting it so tight? Link to comment Share on other sites More sharing options...
PeterW Posted September 13, 2017 Share Posted September 13, 2017 17 minutes ago, recoveringacademic said: Trade names for membrane and tape please. Thanks Ian Tascon ProClima tape Intellio membrane Link to comment Share on other sites More sharing options...
ProDave Posted September 13, 2017 Share Posted September 13, 2017 It's actually Tescon Vana (made by Pro Clima) tape, in case you have trouble finding it. I got it cheaper from Germany via an ebay seller. Siga Sicrall is another one but even more expensive. Link to comment Share on other sites More sharing options...
richi Posted September 13, 2017 Share Posted September 13, 2017 (edited) If rendering/plastering onto something like aircrete blocks (e.g., Thermalite), then consider starting with a thin PVA mix beforehand (something like 25% PVA to 75% water, I think, but don't quote me) Edited September 13, 2017 by richi Link to comment Share on other sites More sharing options...
bassanclan Posted September 13, 2017 Share Posted September 13, 2017 Instead of s&c you can use Gyproc Soundcoat Plus as a large coat (I assume internal) which you can make into a slurry and apply with a broom. That's what I did Link to comment Share on other sites More sharing options...
ToughButterCup Posted September 13, 2017 Author Share Posted September 13, 2017 Excellente Tenente! Magnifico! I feel a test patch coming on. Photos of the mess to follow. Hmmmm, a bit of me is wondering how I test a test patch? I mean, how do I know the test patch works? Answers on a postcard to Salamander Cottage, near Forton Services on the M6...... Link to comment Share on other sites More sharing options...
Jeremy Harris Posted September 13, 2017 Share Posted September 13, 2017 Parging with a wet sand/cement mix (lots of cement) is a standard detail. For big areas use a soft broom. It works well, and has been used for years to seal up leaky brick/blockwork. A web search on "parge coat" will reveal more than you ever wanted to know about it................... Link to comment Share on other sites More sharing options...
ToughButterCup Posted September 13, 2017 Author Share Posted September 13, 2017 Thanks. "Another Fine Steep Learning Curve you got me into Jeremy." (Apologies to Stan) Link to comment Share on other sites More sharing options...
PeterW Posted September 13, 2017 Share Posted September 13, 2017 44 minutes ago, recoveringacademic said: Hmmmm, a bit of me is wondering how I test a test patch? I mean, how do I know the test patch works? Get a 12" long piece of 32mm waste pipe, a camera, stopwatch and piece of purple fabric. Ask Debbie to hold the camera and the stopwatch. Cut a hole in the fabric and place it over your head with the hole over your cheek. Place your mouth firmly over the pipe and then put the pipe on the wall test patch. On Debbie's count, deep breath and blow hard into the tube. At 10 seconds, Debbie should take a photo of the colour of your cheek against the cloth.... Post the photos on here and we can provide the expert view of which is best based upon the colour differences....... 3 Link to comment Share on other sites More sharing options...
Russell griffiths Posted September 13, 2017 Share Posted September 13, 2017 Ok so I'm confused ? Not hard as I'm a bit of a thicko. If your blocks are core filled and your posi joists don't penetrate into the wall how and where are you going to get air loss. Is is it normal practice to air seal icf or is it just the type you have used. Link to comment Share on other sites More sharing options...
ToughButterCup Posted September 13, 2017 Author Share Posted September 13, 2017 2 hours ago, Russell griffiths said: [...] Is is it normal practice to air seal icf or is it just the type you have used. Durisol is 65% air. How and where? Everywhere 1 Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now