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sand cement interior airtight layer


Moggaman

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30 minutes ago, Iceverge said:

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. 

The top of the conduit would be behind the plasterboard ceiling so the plasterer wouldn’t be able to affect this.

 

The Silcone in the box would be applied at the end of the first fix, so it will be dry and won’t be in the way for second fix.

stripping outer sheath of twin and earth has to be inside the box. So that’s sealed too..

 

if there is no conduit it’s just the silicone at the bottom to deal with.

 

 

 

 

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1 hour ago, TonyT said:

The top of the conduit would be behind the plasterboard ceiling so the plasterer wouldn’t be able to affect this.

 

The Silcone in the box would be applied at the end of the first fix, so it will be dry and won’t be in the way for second fix.

stripping outer sheath of twin and earth has to be inside the box. So that’s sealed too..

 

if there is no conduit it’s just the silicone at the bottom to deal with.

 

 

 

 

what seals the blockwork in the chase behind the conduit? I had numerous leaks here that i found as the chasing the blocks had left a thinner mortar bed etc and more chance of gaps into the cavity. It was solved with some airtight sealant and paint before first fix.

 

Do you silicone the chase behind the conduit before you put it in?

 

How did you deal with the blockwork above the plasterboard? 

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I suppose a parge coat could be applied to the chase, but if it’s getting plastered anyway the wet plaster will seal it up.

 

no silicone in the chase, it’s in the conduit either end of installed or just the box if it’s surface clipped.

 

blockwork above the plasterboard - not sure what you mean

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Prehaps I should have asked what the plasterboard was fixed to? 

 

If it's the bottom of the joists then you'll have to deal with plastered blocks between and for the thickness of the plasterboard below the joists.

 

If you use a service cavity then you'll have the thickness of the blocks unplastered in the service cavity. These are potential leakage areas.  

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I'm trying to find the sweet spot between what will give us a reasonable attempt at airtightness, and simultaneously my builder can do without too much expense or heart ache on his side, when he would prefer to be getting on with the house in the way he knows best.

 

-Plan to parge the external masonry walls (from the inside).

-We have a poured ground floor and will take the parge down to ground, maybe needing a bit of foam or blowerproof in the corners, hoping for a simple and good result from that.

-Then to sandwich an AVCL between the 1st floor double boarded ceiling plasterboard (as one layer of PB already done), where AVCL is lipped around the top room edges / corners, bonded in to seal those edge areas.

 

An awkward area is the ground floor ceiling joist hangers which are hung onto timbers that are attached laid against the wall. A fair bit of first fix cabling and plumping is in the joist cavity areas, so unsure how well he would be able to trowl the parge up into the joist returns, and obviously cant get behind the main timber against the wall which the hangers are nailed to.  It feels like the best attempt would be to trowl up in-between the joists where they are clean (no 1st fix elements) and instead using foam or blowerproof paint for the busy ones.  I have one pot of blowerproof coming as a test.  Am guessing where they can return the parge between joists, that a seal will be needed to manage the interaction between the page and wood. Then where that parge and block work is chased out for back boxes and cable runs, I guess blowerproof or re-parge over those cavities, including top and bottom of any conduit with silicone.

 

Need to think about the two internal stud walls already in place on the first floor, I can't see how I can AVCL over the top of those, and so how to cut them off from the cold loft.  I will change strategy for the future walls.  It is a very busy crawlspace loft with diagonal timbers everywhere, but at least the rock wool isn't down, so potential to perhaps paint or sealant from above with the insulation put on afterwards.  I could instead take off some plasterboard (not skimmed yet, so just unscrew) from the studs and tape or seal the stud to plasterboard joins from the inside.

 

To confirm, what is the preference of persons here for airtightness of back boxes in studs or timber frame where the depth of the box is likely to require you punching through your VCL?  We have already purchased regular metal back boxes for switches and sockets.

 

Happy to adjust plan if there are obvious flaws that anyone can spot.

 

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1 hour ago, Iceverge said:

You're playing catch-up by the sounds of things. Don't worry persistence and patience will get you there. 

 

How hands on are you with the build might I ask before I start making suggestions?!

 

Yes it is a best effort at this stage. I am minimal hands on due to injuries and lack of time with the kids and full WFH. That said the builder rates are very good for the quality I get due to them being family friends.

Edited by tanneja
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The best thing you can do is make sure your builders understand the concept in that case and the level of detailing required to get a good result. 

 

I'd scour eBay and buy a car fan, wire and some crocodile clips to make up a test fan in a sheet of OSB or ply for one of the windows. Clip it onto the car battery to depressurise the house, (best to leave the car running I found as it draws a lot of current and flattens the battery). 

 

Go searching for leaks with the back of your hand. This will do more explaining about the nature of airtightness than anything else I could say. 

 

https://www.ebay.co.uk/itm/2006-2011-LEXUS-IS220-2-2-D-RADIATOR-FAN-422750-1620-/203184726071?_trksid=p2349624.m46890.l49292

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7 hours ago, Iceverge said:

The best thing you can do is make sure your builders understand the concept in that case and the level of detailing required to get a good result. 

 

I'd scour eBay and buy a car fan, wire and some crocodile clips to make up a test fan in a sheet of OSB or ply for one of the windows. Clip it onto the car battery to depressurise the house, (best to leave the car running I found as it draws a lot of current and flattens the battery). 

 

Go searching for leaks with the back of your hand. This will do more explaining about the nature of airtightness than anything else I could say. 

 

https://www.ebay.co.uk/itm/2006-2011-LEXUS-IS220-2-2-D-RADIATOR-FAN-422750-1620-/203184726071?_trksid=p2349624.m46890.l49292

This is really appreciated @Iceverge

 

Can I ask a nonsense question?  Our house is part old construction (solid 215mm brick, with decent condition sand cement external render) and part new (300mm double medium density block skins with insulated cavity).  The old build is to be covered with EWI (100mm EPS) and then both think coat render silicone silicate over top.  Question is can the parge coat be applied externally for the old build under the EWI?  Seems like it would still be behind the insulation.  Presumably for the new build it needs to be on the inside to be on the inside of the insulation.  Just wondering if, weather permitting, an external coat prior to EWI would be simpler to manage the joist joints.  Maybe it wouldn't stand up to even a short duration in the elements.

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1 hour ago, tanneja said:

This is really appreciated @Iceverge

 

Can I ask a nonsense question?  Our house is part old construction (solid 215mm brick, with decent condition sand cement external render) and part new (300mm double medium density block skins with insulated cavity).  The old build is to be covered with EWI (100mm EPS) and then both think coat render silicone silicate over top.  Question is can the parge coat be applied externally for the old build under the EWI?  Seems like it would still be behind the insulation.  Presumably for the new build it needs to be on the inside to be on the inside of the insulation.  Just wondering if, weather permitting, an external coat prior to EWI would be simpler to manage the joist joints.  Maybe it wouldn't stand up to even a short duration in the elements.

no nonsense questions only nonsense answers!

 

yup it can be done like in the below picture with airtight paint. the trouble is thought that it’s difficult to join to your roof airtight layer. if you’re joining to the windows with an external parge  coat you’re very weather dependant to get tapes to stick. it’s impossible to pinpoint leaks using a depressurisation fan afterwards too.

 

Have a look through Philips from prodomos blog, i found it useful. I also bought all my airtightness kit from him although i’m not sure if he can supply GB post brexit.

 

https://www.prodomo-ireland.com/prodomo-ireland-s-blog/

 

ED877111-07FF-438F-A8FA-92F162F36C3F.jpeg

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On 20/01/2021 at 00:59, Iceverge said:

The best thing you can do is make sure your builders understand the concept in that case and the level of detailing required to get a good result. 

 

I'd scour eBay and buy a car fan, wire and some crocodile clips to make up a test fan in a sheet of OSB or ply for one of the windows. Clip it onto the car battery to depressurise the house, (best to leave the car running I found as it draws a lot of current and flattens the battery). 

 

Go searching for leaks with the back of your hand. This will do more explaining about the nature of airtightness than anything else I could say. 

 

https://www.ebay.co.uk/itm/2006-2011-LEXUS-IS220-2-2-D-RADIATOR-FAN-422750-1620-/203184726071?_trksid=p2349624.m46890.l49292

Going around the house feeling for leaks is presumably a labour of love.  Did you use additional devices to quantify the ACH and Pa when performing this exercise?

 

Also super appreciate the external approach information.  Fortunately where our joists go into wall plates, I think an internal parge ove rthe walls, with blowerproof around the edges of that wall plate should be really effective.  If the joists were into the wall then that would presumably be much more work with ensuring airtightness around the joists.

Edited by tanneja
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It's not difficult, just take your time.

 

After various experimentation with a beesmoker, Joss sticks, talc etc I found the easiest way was the back of your hand for the larger leaks, it's surprisingly sensitive.

 

Then I shoved a long candle into a piece of conduit for the minute pinholes. This was remarkably accurate at finding weak spots with the added advantage you don't have to do any climbing or bending down 

 

No special equipment, some on here have DIY'd manometers but it's not easy to make an accurate one  The guy with the blower door did the proper measurements 

 

Are your joists built in already? 

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  • 6 months later...

A bit of a resurrection here.  Airtightness throughout the house has seemed to go well, plan a test once the spots go in upstairs and able to hood over them, but VLC and parge throughout.

 

One element of the build that I am uncertain about is the attached garage (has a garage door, a back door to garden and access door to the house).  It was build up to it's current stage before we thought seriously about air tightness.  It will likely be used as a home gym and storage area, unlikely to have a car. I appreciate regs say it can't be an airtight space, so this is more hypothetical.   Just thinking ahead to if it becomes habitable.

 

We are likely to have the garage door just be a fixed, cellotex backed sheet of ply for the foreseeable future due to costs, but at least can make it air tight.  The back door is airtight, and the window / skylight airtight detailing has been done to the best of our ability.  The issue is the room construction is double skin (rock wool filled) breeze blocks, ceiling is vaulted rafters with regs thickness cellotex intra and under the timber structure, but no air tight layer, all of which which have already been dot and dabbed / screwed PB as appropriate, but not yet skimmed.  .

 

What hope can I have of making this room relatively airtight at this late stage?    Is whole room blowerproof prior to skim a good idea?  Unsure if the skim will take to the blowerproof well enough if used over all the floor and ceiling.  I could just blowerproof the PB joins?  Ask for thicker than usual skim?  Obviously also need to look at all the PB penetrations (sockets etc) and make sure they have appropriate putty / silicone treatment.

 

Obvious solution is to forget about any of these and focus on a good airtight insulated door between house and garage, but exploring all our options.

 

Any guidance would be much appreciated.

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1 hour ago, tonyshouse said:

Don’t allow dot and dab!

I’ve specified dot n dabbing on 2 current new builds where I’m the project M&E coordinator. I’m expecting sub 0.3 ACH results from both blower tests. One being booked in presently, now the windows and doors are nearly all in, so I’ll try to remember to post the results. We’ll be doing both an ‘interim’ and an ‘as-built’ test on each. They’re both woodcrete ICF. 
 

You can do anything you like, as long as someone has a handle on quality and is there to highlight the not so obvious points of failure and mitigate against them as required; ( eg liquid airtightness membrane / closed cell foam / tapes / mastic etc ). 

Edited by Nickfromwales
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On 26/07/2021 at 00:06, tanneja said:

What hope can I have of making this room relatively airtight at this late stage?    Is whole room blowerproof prior to skim a good idea?


need to stop the air movement behind the wall boards. Can be done but needs patience.
 

Get a decent foam gun and some low expansion foam. Now drill a row of 10mm holes about 150mm down from the ceiling and same up from the floor about 150mm apart and then slowly squirt foam into each hole. It’s tedious but go slow as the foam needs to form a continuous band top and bottom. 
 

Do the same at any corners and doors and you’ll reduce the risks of air going behind the boards. Not perfect but unless the plasterer did full top and bottom beads of adhesive you’ll have gaps. 

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Thanks @PeterW.  I could ask the builders to multitool out the bottom and top 2" of PB and then have a bonding coat infill, then skim over the lot, and then have blowerproof behind services penetrations.

 

I will need to ask him to remind me what the ceiling make up is, unsure, due to it being a garage whether there is an airtightness layer / vcl in the vaulted ceiling.  If not, don't know what to do about that.

 

You can seemingly get a blowerproof spray guy out for large areas, this room is 6x6m with high vault.  Best it is expensive.

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