Insulating around window support bars

aidanki

Currently fitting the insulation tape around the bars which hold the windows in place. Some aren't flush with the insulation and walls. Could put my finger between the bar and the insulation.

How is best to address that.

Biker1

The airtightness tape must be fitted to the window, across the insulation and onto the block on all four reveals. Make sure to remove the foil from the frames first.

BryanF

suggest taping from window to internal block. The block needs a coat of plaster and primer to allow the tape to adhere. Try to get contega tape, the 200mm role might stretch the cavity.

aidanki

We were told we needed to cover the bars first as I have shown in photo.

Then cut a short piece and cover the corner 3" X 3" say

Then finally long strips all the way, left right and up and down.

AND all before any plastering

It's my brother house and I'm helping him

Are we doing it incorrectly

8" cavity in that wall

aidanki

https://www.boards.ie/discussion/comment/120947286#Comment_120947286

Should there be one coat of plaster before we put on the tape

BryanF

Where is the proposed air-tightness layer? It’s normally the inner block face / reveal. What you describe is fine as pre work before taping the windows. The 3’’x3’’ corners need to reach the block. As long as the end result is a full wrap all around the windows to the blockwork. Just a quick rough plaster on the reveal of the block, smooth it as best you can, use the air-tightness tape primer and then tape from windows to primer. In the end the tape should be covered by the plaster. They’ll need a board or mesh at where tape spans the insulation cavity closer, or maybe your using insulated plasterboard at the reveals?

SodiumCooled

https://www.boards.ie/discussion/comment/120947286#Comment_120947286

Sorry to hijack but I am seeing a lot of conflicting information on whether the airtightness tape goes onto the block directly or needs to be plastered first. My engineer, the airtightness company and other tradesmen who I have asked in passing all say it from the window to the block and either plaster over it or in my case the engineer has specified plasterboard on the reveals and then skimmed. I am a bit confused really with the conflicting info as some people on line say as you have while others say its directly to blockwork with the majority I can see saying direct to blockwork.

Yellow_Fern

Seen a lot of people just dob tape over the bar, making no allowance for the fact it is raised, leading to corners not sealing.

As for can tape go directly, i think there are ways to do both, but remember the block is not airtight.

10-10-20

The way I see it, the block is essentially porous. It's also somewhat friable (likely to shed loose particles) and not a fantastic bonding substrate due to the unevenness of the surface and also due to incomplete mortar joints. I have seen some tapes pulling away from blocks and leaving an air-path around tight points such as window mounting bars.

Reviewing Isover's site, as seen in their video they do not require that the block be prepared prior to the application of their Vario Bond tape, but they do bring the tape out to about 2 to 3cms from the external edge of the block and also wrap the front facing portion of the window lintel.

https://www.isover.ie/products/vario-bond#related-video

Personally I've used SBR as a primer on a retrofit as the lintel block had plaster remnants and dust embedded as well as a small amount of loose material, but this isn't recommended anywhere that I have seen.

I see that there are air-tight primers available elsewhere, I'd be using that in future cases.

10-10-20

And as for the suggestion of rough plastering the blockwork, with the greatest respect to BryanF - that's creating another physical intervention for the block-layer/plasterer, requires time to dry and also adds a small amount of build-up of the thickness of the reveals; so it's adding cost and complexity to something that already seen as somewhat as a costly nuisance (those tapes aren't cheap). I'd much rather just roll on some approved primer to the block and have it ready within hours.

aidanki

what do I do where the insulation is back from the bar as in my picture in the first post

10-10-20

https://www.boards.ie/discussion/comment/120965109#Comment_120965109

Possibly nothing as it's behind the air tightness layer, but I would suppose any packing such as low expansion foam would be suitable and then cut-back slightly to maintain allignment at the edge of the support?

BryanF

https://www.boards.ie/discussion/comment/120960518#Comment_120960518

Can you clearly define where the air-tightness layer is. So if you’re plastering the blockwork over the tape that’s fine. But if your eng is putting plasterboard in reveals where is the air-tightness layer?

https://www.boards.ie/discussion/comment/120960926#Comment_120960926

No problem with a primer, assuming it s suitable as the air tightness layer.

SodiumCooled

https://www.boards.ie/discussion/comment/121003792#Comment_121003792

I assume it will be plastered with sand and cement first and then plasterboad followed by skim - though I am not sure why the plasterboard would be necessary (except under the window board maybe) as couldn't the plaster be just skimmed over? It says plasterboard on reveals in one place on the plans and sand and cement in another so that's why I was confused - will be confirming with him anyway.

As an aside would plasterboard which would be sealed with skim not be airtight?

BryanF

It’s all about continuity. Best thing you can do is draw it out on paper first. Also before you keep going on site, why not get the air tightness tester to advise on the details.

SodiumCooled

Hi All, sorry to drag up an old thread but its very relevant to my previous conversation above. Airtightness taping was done on windows with the plasterable tape and I was working of the assumption that the reveals would be sand and cemented but with slabbers working in the house now they have said they will be slabbing the reveals once finised the ceilings - I questioned it and they said that's how its done in every house. Asked the plasterer and he said he never puts sand and cement on reveals anymore and would not be willing to plaster over airtightness tape as he doesnt trust it not to crack.

So half my revel is covered with the tape but the the other half will be bare blockwork and a slab will be going straight over it. I know its not the absolute best practice for airtightness but my feeling is that it shouldn't cause major issues either or am I wrong?

Biker1

If the plasterer is not willing to do what is required then get some airtight paint and paint any bare blocks before it's too late. Any blocks around reveals and above suspended ceilings are a major air leakage issue on all houses I test.

SodiumCooled

https://www.boards.ie/discussion/comment/122164927#Comment_122164927

There wont be time unfortunately I am already racing against time to get the strip painted on the blocks that will be left between airtight membrane and plaster upstairs due to the thickness of the insulated slab on the ceilings (if you get where I mean). I will just about get that done this evening ahead of upstairs slabbing tomorrow - it would be probably a full days work minimum to paint all the reveals and that's not going to happen between now and Thursday.

Does the slab and skim coat not do a fairly good job in sealing it up? the slab will be stuck to the wall in my understanding. I have spoken to two different people since (a carpenter and my blocklayer) and both said this is how they see it done in every house they work on (including their own recently built house in the case of one of them).

Biker1

"We have always done it this way" does not make it best practice. An incomplete airtight layer will lead to unwanted heat loss regardless of what anyone says. I have been testing houses for the last 15 years and very few houses come close to an easily achievable standard. The backstop in the regulations is 5m3/m2/hr at 50pa so people think if they get a result better than that they have a good job done. 1m3/m2/hr at 50pa would be a better target.

sydthebeat

https://www.boards.ie/discussion/comment/122164685#Comment_122164685

you should be doing both.

airtight tape all window frames back to the blockwork, then use a plasterboard as the reveal, set into an L angle on the window frame to ensure plumbness. Skim finish to everything then.

SodiumCooled

https://www.boards.ie/discussion/comment/122166499#Comment_122166499

This sounds like what we are doing? Tape is going from frame back over the remaining cavity which has PIR to close it and back about half way in the revel. What I’m being asked to do then is get the slabbers to use plaster board as the revel with the J angle at the window. Similar for the bottom with a slab going on (which the window board will sit on.

sydthebeat

https://www.boards.ie/discussion/comment/122167873#Comment_122167873

yep, sounds right.

youre getting teh ability to best employ your air tightness strategy, plus your getting a more solid reveal. Caulk seal the plasterboard and windowboard (all around!) join for extra precaution.

SodiumCooled

https://www.boards.ie/discussion/comment/122169105#Comment_122169105

Thanks, so is the fact the blockwork in the revel that is not covered by the tape is not being plastered with sand and cement either not an issue for the airtightness then as has been suggested? e.g, there will be part of the reveal with platerboard going onto bare blockwork?

sydthebeat

https://www.boards.ie/discussion/comment/122169191#Comment_122169191

no, you should apply a thin sand and cement layer there to seal the inner leaf blockwork. The plasterboard strip can also be fully bonded to the blockwork, instead of spot bonded, to seal the blockwork as well.

Dublin City Handyman

Your Plasterers are correct..no need to sand and cement the reveals..