VCL over parge coat?

[James94]

I am going to either PIR the ceiling and tape all joints or use a avcl membrane then use a tape such as the fentrim 20 or pro clima contega (any other suggestion would be great) to seal to the blockwork and parge up to. Similar to this photo I have found. 
 

Do I need a VCL on the walls? Over the parge coat? Standard cavity wall build up by the way.

 

Thanks James 

[Russell griffiths]

No your parge coat is the vcl

as long as it’s done well, you need to look at how joists will be fixed to the walls and how you seal around them. 

[tonyshouse]

Where is the air barrier? How does it join to the adjoining ones? 
 

vcl can be an air barrier - I wouldn’t trust parge coat as a long term air barrier blocks look like aircrete and these are notorious for cracking and round joists can be very problematic an joists shrink too. 

[James94]

Joists are on hangers, I hadn’t heard of tony trays at that stage so missed the chance to install them, now I’m going to try my best to seal around these.

 

I presumed the air barrier on the photo I attached was the parge coat that laps over the membrane to create a continuous air tight seal.

[Russell griffiths]

You can buy a liquid air sealing paint, paste type stuff, you either paint it on thick around all joist ends and penetrations, or spray it. 

I wouldn’t use sand and cement for any detail work as it will dry crack and leave gaps. 

Flexible is your friend. 

I have probably used 25 sausage tubes of air sealing paste to go around all the nooks and crannies. 

[tonyshouse]

Where parge laps over membrane it needs a key, typically EML fixed over the edge, we used 50mm stapled to plate or blocks 

[James94]

I had considered blowerproof around joist ends, it is pricey though.

 

So my understanding was these tapes offer a key for the plaster(see photos attached). Would you say that EML offers a better key and could I then go for a standard air tightness tape or do away with the tape completely? 
 

Thanks James

[Russell griffiths]

Blowerproof is a bit expensive, but if you think you will use 3-4 tubs then £200-£250 is not a lot for some good insurance. 

[James94]

I’m going to buy the blower proof for joist ends just to be safe.

 

The drawing below shows a partition wall leading to a vaulted ceiling. This is how I had planned it. I would like to know if we should insulate the stud wall with PIR for thermal insulation down to ceiling level and acoustic for sound insulation down to the wall plate as these stud walls separate bathrooms from landing. Whilst maintaining the VCL.

 

Thanks James

[Russell griffiths]

Those loft cheeks should have ;100mm pir in the gaps and 50mm pir over the whole face covering all the studs. 

[James94]

Sorry for not replying sooner, are you classing the cheek as the stud wall that sits on the block work up to the ceiling? Is that the proper name for it?

 
I assume the 50mm is to stop cold bridging through that stud? The only issue with that would be creating a difference in levels to the blockwork, and encroaches to much on window frames. 
 

Thanks James 

[tanneja]

I've found myself looking at https://www.ecomerchant.co.uk/pro-clima-contega-solido-sl.html tape for our already plastered upstairs rooms which I would like to have some airtightness.  Rooms are already boarded directed onto the ceiling joists so no chance to fit a membrane there.  I can double board with a sheet membrane on the ceiling, but don't have the space to double board the walls, so would likely need a tape for all other PB joins in the room / the room corners.  I guess we will have a plasterboard based airtightness. 

 

Is this tape any good? Likely to need 2-3 rolls per room at around £40 a go.

[Olf]

5 hours ago, tanneja said:

Is this tape any good?

I used Contega PV to join the membrane to the wall, Solido looks like a different variant of that product line. The fleece holds the plaster well, but the tape is so-so: I managed to remove it easily when made a cockup, something I cannot say about normal tapes (Proclima or Gerband).

Regardless, with Solido you'll end up paying big buck and having thick skim to cover it. I'd look for some sealant instead - I use https://www.soudal.co.uk/pro/products/sealants/acrylic-sealants/acryrub-sws/acryrub-sws-310ml around windows, it's airtight and paintable, was about £3 per tub. You can check their Acryrub line for something with less flex, so potentially cheaper. Or other supplier for that matter, CT1 seems to have some good fame here, though not sure if paintable/plasterable

[James94]

Not sure how it would work on a room that is already plastered, we haven’t used any of the tapes or vcl yet as still adding PIR to roof.

we got tape from a German site, if you search it on here you will find it, not sure if it’s cheaper.

Regards. James

[tanneja]

Thanks for the advice.

 

I think for the plastered room we will double board the ceiling with an AVCL between the boards, then remove the top 4 inches of plaster board from the walls, have this AVCL lip into that cavity, attach slim batons over the AVCL in that cavity to hold in place and give something for wet plaster / bonding to hold on to, filling in that top 4 inches with this wet plaster / bonding.  I didn't recall but at my request the builder internally rendered the brick walls prior to dot a dab at my request in the hope of some sound performance, so hopefully with this ceiling approach the leakage from the room could be ok.