air-tightness at window reveals

Wavehopper

Hi all,

I have 100mm outer leaf + 150mm cavity + 100mm inner leaf where the outer leaf at window reveals extended out ~40mm past inner leaf to allow for 37.5mm insulated plasterboard each side of window reveal. I also have xtratherm cavity closer used to close cavity each side of window (single lip on inside).

The problem I have is that my air-tightness contractor can't use air-tightness tape between frame and plasterboard. He also doesn't want to use membrane in this location so has suggested that I build out the gap with bonding compound + 12mm ply + 12.5mm plasterboard. Air-tightness tape attached between window frame and ply and then plasterboard put on over this.

Is there any issue now with this given that I won't be able to use the insulated plasterboard in the gap left deliberately for this?
Would it be any addition to use expandable foam in the gaps between blockwork and ply (in-between bonding compound) or would this be a waste of time in terms of insulation?

I could use 25mm PIR board + 6mm ply + 12.5mm to build out the reveals so would this be a better solution or does the additional insulation at this point add much value?

Thanks

mickdw

This doesnt sound right. Why can he not tape from window frame using membrane back to the inner block wall? and slab over it.

Wavehopper

Hi Mickdw,
He just said it was more difficult to achieve air-tightness result by using tape and membrane back to the blockwork.

I can see why he wouldn't want to use membrane at the bottom of the window where fitting a window board could puncture the membrane but I can't see why it wouldn't be a good solution each side of the window frame.

Is there an issue having non-insulated gap between blockwork & cavity closer up to ply/plasterboard with the solution being used?

Thanks.

braftery

Hi there,

I am really confused by what your air tightness guy is saying also.

It is pretty standard for fitting air tightness tape from the frame of the window back to the block. There are special sealants sold by the air tightness manufacturers for this.

I am also a little confused about what exactly is in place there now.

The cavity closer is fitted.
Your window is fitted, using steel straps back to the inner block ?
I am assuming the gap between these two is filled with an expanding foam ?

If all the above is already in place, I dont see any reason why that air tighness tape cannot be positioned from window frame to block on all sides.

On the bottom the placing of the window board can be done without nailing or screwing into the block below. Or if it must be screwed, the screws can be positioned further inside than the airtightness seal.

tred

I have the same setup. My air tightness installer, ran a bead of sealent along the blockwork. Affixed the tap to the window and then to the blockwork using the sealent to stick and seal. Slab then goes over this. Have you a
Pic of the window ???...Maybe i am missing something here!.
maybe its depends also on what product hes using.....Some arent as good on the blockwork as others...

creedp

Hi I a little confused by this also as I thought you could simply run the airtightness tape around the perimeter of the window/door attaching the other side directly to the block without the need for any additional dealants.

@Tred - why do you need the bead of sealant to stick the tape to the block? I though the tape would stick to the block unaided. If not I need to seriously rethink my approach.

If this is the case does it also apply when taping the hollowcore membrane to the block wall and the intello ceiling membrane to the wall?

Wavehopper

Hi,
My problem is that there is too big of a gap between edge of window frame and cavity closer so we can't use standard tape here.

It's also not possible to put on insulated plasterboard and then tape to this as skim won't work with current tapes. I believe that some air-tightness suppliers are working on new tapes that could be used in this detail but they are not certified yet.

My installer is reluctant to tape membrane to window frame and attach to blockwork due to the difficulty to fix the insulated plasterboard....not possible to bond insulated slab to membrane and if you drill & fix via mushroom fittings then you puncture the membrane.

Proposed solution is to fix sheets of ply or timber boards to blockwork and tape from window frame to the timber and then fix plasterboard. If there are any gaps, fill these with expandable foam (some of these foams have good insulation properties)

I don't have a picture at hand but can post one later

tred

creedp wrote: »

Hi I a little confused by this also as I thought you could simply run the airtightness tape around the perimeter of the window/door attaching the other side directly to the block without the need for any additional dealants.

@Tred - why do you need the bead of sealant to stick the tape to the block? I though the tape would stick to the block unaided. If not I need to seriously rethink my approach.

If this is the case does it also apply when taping the hollowcore membrane to the block wall and the intello ceiling membrane to the wall?

I am not sure from Mods if I am allowed to say what I used, so if this is edited, pm me, but basicaly for Siga, they used a bead of the blue sealent Siga primu along the block, and then tape from window to this. If you were to do it urself, for siga anyway, ud use the primur, and let it dry for a few hours, then stick, or they have a new product which is primur roll, cured and ready to stick too. So back to OP. Why can you use tape, some membrane, tape again?. its as much the same labour there than building it out, one would think..

braftery

I still cant see the problem.
If you could make a drawing it might be easier to understand.

Questions:

How are the windows fixed in place ?
Is the gap between the window and the cavity closer filled with expanding foam ?
How big is the gap between the edge of the window and the edge of the block ?

braftery

Creedp,

The product that Tred mentioned works with a sealant.

The block has an uneven surface (pitted) the sealant bead put on the block will filled those pits and make sure the seal is airtight. The tape is flat and might not make the seal.

creedp

Thanks Tred and Braftery

I have been looking at the ecological building system website and it would seem the Contega FC and Orcon F products are the SIGA equivalents. Although there is no delay using Orcon - you can simply apply it and stick tape directly to it. It would seem however that if you do this you have to use plasterboards for the reveals i.e. scratch the reveals, then apply orcon and tape and then apply plasterboard and skim. An alternative is to bury the tape into the plaster as it is being applied but it seems it is difficult to get plasterer to work with this approach.

I've also spoke with a builder who says he uses a yellow siga tape that can be stuck directly to quinnlite blocks as they are smoother than std blocks so avoiding the use of glue/bead. I might pursue this with SIGA. Anybody heard of this tape and have any comments about using it for window/door reveals or even sticking ceiling membrane to walls when you have quinnlite blocks?

Thanks again

L driver

Wave hopper,
Get the 12/48 tape, cut into lengths for the window. Now get the breathable membrane and cut it wide enough to go from the frame to half way on the internal block,allow a bit of slack(trial and error). Now cut the membrane to length to suit the already cut tape. Stick the membrane to the 48mm side of the tape. Now stick the 12mm side of the tape to the window frame, taking care to only come in the 12mm from the frame edge. Next apply a line of the adhesive to the internal block, half way between the middle and the edge nearest the cavity. Gently press the membrane against this adhesive. Do this for all sides.
Now get the 30/30 tape and join all the membranes in the corners. Repeat this for all windows and doors!! When all air tight work is done do your blower door and sort any weak spots.
Now get 12mm stop bead/j bead and fix it around the window frame with small self tappers, it will be sitting on top of the 12mm folded tape.. hence neat job earlier! Build out inner half of internal leaf to suit inner edge of the 12mm j bead, lintel and window board level should be ok. Now cut the plasterboard to suit the head and reveals, allow over hang for scratch coat, fit the plasterboard into the head first and stick to the inner half of the lintel with bonding compound. now fit in the reveals and screw to build out or stick. Use 12mm ply for under the window board, which can be screwed to when fixing the window board.
Stand back and smile and wonder why do we still build with cavities, I have the t shirt!:mad: Not simple, time consuming but probably the only way out Sorry.

soldsold

My detail is very similar to Ldriver, but instead of using channels at the window I screwed a strip of plywood to the window top bottom and sides that was about 20mm wider than the window frame so it sticks out on the cavity side and I can screw the plasterboards to this plywood.

I'm also using webbfix adhesive to fix the plasterboard to the window reveals as it's a foaming adhesive that shrinks to pull the plasterboard tight to the reveals.

If needed I'll drill pilot holes on the plasterboards before I fix them and put a circle of airtight silicon around the holes so if I puncture the airtight membrane it will stay sealed. However I understand that if you screw into an airtight membrane tightly it seals itself?

I used the trick of putting airtight mastic half way out the inner block reveal so the adhesive and mushroom fixings won't break the airtightlayer here.

L driver, how did you deal with RSJ's over patio doors etc?

L driver

Soldsold,

If the rsj is directly below the hollow core slab, then you might be lucky that the drop ceiling will cover the depth of the rsj, allowing for the membrane wrapping the hollow core to be stuck just below the rsj. If the RSJ is just over the door...
noggin out the rsj first, can squeeze in some insulation where room, do as described with tape and membrane to top of door but membrane has to be longer and wider and cut like a capital T upside down. Tape as above post with12/48 to top of door frame. Tack the membrane to the noggins first, then apply a line of adhesive around the RSJ and stick the membrane to it. It gets kinda tricky just under where the rsj is sitting but with a little care and inventiveness it can be sealed. Next cut a plaster board or 2 if ope is wider than 8', making it a little longer and higher than the rsj. Depending on space under the lintel, screw a 2x1 or some of the angle used for hanging the suspended ceiling(right angle stuff) to the bottom inside of the plasterboard. This should be slightly shorter than the door ope and centered on the plasterboard to allow the board to cover the length of the rsj. Screw the board to the noggins keeping the bottom of the board level with the top of J bead that i fixed to the top of the door frame. This allows for the head to fit into the j bead and screwed to the 2x1/right angle metal.
Sand and cement to the plaster board and skim the lot.
Note; noggins can be left proud to allow for more sand and cement,bonding needed about edges then.
instead of plaster board use 9mm osb and expanding metal, sand and cement the lot.
either of the 2 options have to be cut bigger than the rsj and will probably look like [ turned 90 degrees if you know what I mean, depending onhead height.
Hope that helps

gears

creedp wrote: »

Thanks Tred and Braftery

I have been looking at the ecological building system website and it would seem the Contega FC and Orcon F products are the SIGA equivalents. Although there is no delay using Orcon - you can simply apply it and stick tape directly to it. It would seem however that if you do this you have to use plasterboards for the reveals i.e. scratch the reveals, then apply orcon and tape and then apply plasterboard and skim. An alternative is to bury the tape into the plaster as it is being applied but it seems it is difficult to get plasterer to work with this approach.

I've also spoke with a builder who says he uses a yellow siga tape that can be stuck directly to quinnlite blocks as they are smoother than std blocks so avoiding the use of glue/bead. I might pursue this with SIGA. Anybody heard of this tape and have any comments about using it for window/door reveals or even sticking ceiling membrane to walls when you have quinnlite blocks?

Thanks again

Regarding using SIGA Sicrall, while it might stick to those blocks it wont stay in the long term, you need to seal the blocks surface with SIGA Dockskin it's basically a paint on primer.

L driver

good point Gears,
the tapes are not to go an the blocks directly

soldsold

I treated concrete lintels exactly the same as the inner blocks, ie a bead of airtight mastic halfway out the lintel And sticking the airtight mebrane to it, leaving room for mushroom fixing the plasterboard.

For the rsj's I cut a strip of membrane wide enough to go from the top of the window out to the rsj, and up a few inches over the Top of the rsj ie to the blockwork above. It's tacked to the timber nogging that fills up the space in the rsj just go hold it in place, and covered with plasterers expanded metal for a sand and cement finish.

Plasterboard is then mushroom fixed to the rsj but this is not going to be done till the airtight test is done

L driver

are you using an insulated slab on internal walls soldsold? I find using bonding compound on the under side of the lintel much better/neater and safer, I don't like drilling concrete lintels in case of cracks

soldsold

Good advice L driver, I'll probably use bonding compound on one spare lintel and webbfix adhesive on another then let them set and see which has the best grip. Will still need to fix through the rsj though on the bottom of the rsj and I'm not confident mushroom fixings are the way to go...

L driver

Just on sticking tape to blockwork, there is one product that can be plastered over if stuck to blockwork or so it is claimed. Which if true would make some air tightness jobs much easier. I'll name the product if the mods allow and see if anyone has experience of it.
Air/wind tightness is so important to any build and it has to be included from day one with all the trades understanding the details, eg how do you tape the overlaps of the roof membrane when the slates are on? People laugh when told that the conduits going to the attic will cause heat loss in their house.

L driver

Soldsold,
Just saw another post from you on air tightness at eaves, great details, I'm sure will come in handy. It's painful work no doubt.

cuculainn

braftery wrote: »

Creedp,

The product that Tred mentioned works with a sealant.

The block has an uneven surface (pitted) the sealant bead put on the block will filled those pits and make sure the seal is airtight. The tape is flat and might not make the seal.

YOu could also tape the windows after sand and cement plaster is applied. This eliminates the need for the extra adhesive, as the plaster is not porus like the block

soldsold

Just for clarification L driver, the details I posted about eaves mastic etc was for wind tightness, of course less wind getting in puts less pressure on the airtightness leaking.

Anyone suggest a way to secure plasterboard to rsj's mechanically? Tec screws seem the best way as I found mushroom fixings can end up loose, also found express nails good but not sure how they will hold plasterboard. Anyone know if tec screws come with flat heads?

Wavehopper

Hi all,
Thanks for your comments on this post.

Thanks L driver for your advice on proposed solution, this looked like a very good solution but my installer went ahead with boarding out reveals with timber end of last week.
Soldsold, that was a good idea where you screwed strips of ply to top/bottom/sides of window frames to fix the plasterboard and silicon around holes for plasterboard…..you should have a good job when you're done.

Braftery, to answer your questions:
The cavity closer is fitted - Yes
Your window is fitted, using steel straps back to the inner block ? Yes
I am assuming the gap between these two is filled with an expanding foam ? Yes
If all the above is already in place, I dont see any reason why that air tighness tape cannot be positioned from window frame to block on all sides. I don't think the air-tightness tape being used is wide enough to go back to blockwork and there were concerns that air-tightness membrane would be punctured if used and insulated slab fixed over it

Tred, here are pictures to explain the detail I had. Apologies for direct links…..haven't figured out how to have these as attachments you can select to open.
Before




After


Window frame will be taped to timber and plasterboard fixed to timber, any gaps between timber & blockwork filled with expanding foam, steel mesh fixed over gap & edge of timber, sratch coat applied flush to plasterboard that will be lift proud to take this coat. Skim finish on everything then. I hope it will still work out ok.

Thanks again.

manufan16

soldsold wrote: »

My detail is very similar to Ldriver, but instead of using channels at the window I screwed a strip of plywood to the window top bottom and sides that was about 20mm wider than the window frame so it sticks out on the cavity side and I can screw the plasterboards to this plywood.

I'm also using webbfix adhesive to fix the plasterboard to the window reveals as it's a foaming adhesive that shrinks to pull the plasterboard tight to the reveals.

If needed I'll drill pilot holes on the plasterboards before I fix them and put a circle of airtight silicon around the holes so if I puncture the airtight membrane it will stay sealed. However I understand that if you screw into an airtight membrane tightly it seals itself?

I used the trick of putting airtight mastic half way out the inner block reveal so the adhesive and mushroom fixings won't break the airtightlayer here.

L driver, how did you deal with RSJ's over patio doors etc?

I have a similar problem at the moment where I returned the air tightness membrane from window frame past reveal to wall so I will have to break the air tightness membrane to fix plasterboard to ICF window inner reveals.

How did you get on? Can you let me know which webbfix adhesive you used?

Do-more

@manufan16, one solution is to measure out and place squares of "radon tape" thick double sided rubbery tape used for joining radon barrier wherever you are going to screw through your membrane or air tightness tape, the radon tape is rubbery enough to self seal around the screw thread.

manufan16

Do-more wrote: »

@manufan16, one solution is to measure out and place squares of "radon tape" thick double sided rubbery tape used for joining radon barrier wherever you are going to screw through your membrane or air tightness tape, the radon tape is rubbery enough to self seal around the screw thread.

Thanks do-more , I'll check that out

New build in sight

Apologies for resurecting an old thread, but we read this thread with interest as we are at this stage and are totally confused! Hope someone out there might still follow this thread and may help us:

We had our windows installed last week and due to lack of forward planning the window sills werent set back far enough for the frame to sit behind the outter leaf, so the frame sits between the blockwork on the outter leaf.

We then had to use expanding foam to ensure the dpc was snag against the outter leaf of block work and the frame of the window.

Now we are left with large cavities to fill, we have filled most of the cavity with expanding foam, more to the outside. However we are confused about how to close them on the inside...

We have 130mm cavity which we are pumping.

We then have left enough room for insulated board 50mm into the reveals.

But how do you all think it is best to seal from window frame to blockwork on inner leaf?

Our engineer suggested just using airtightness tape, but were worried about the fact there will be slack on the tape between the frame and block? How can we get a proper right angle on the tape to ensure the insulated board sits snugly in?
Also the metal straps the window fitters used to attach window to the block are at 45 degree angles so they will effect the insulated board going in also?

Last question, can anyone suggest the best type of tape to use, we do need 4" width due to the large cavity.

Sorry about the long post, hope someone can help us!

rockabaloo

creedp wrote: »

Thanks Tred and Braftery

I have been looking at the ecological building system website and it would seem the Contega FC and Orcon F products are the SIGA equivalents. Although there is no delay using Orcon - you can simply apply it and stick tape directly to it. It would seem however that if you do this you have to use plasterboards for the reveals i.e. scratch the reveals, then apply orcon and tape and then apply plasterboard and skim. An alternative is to bury the tape into the plaster as it is being applied but it seems it is difficult to get plasterer to work with this approach.

Is this true? Can you not just seal the tape to the blockwork and then get the plasterer to plaster over it? Would it be ok to do it this way?

manufan16

New build in sight wrote: »

How can we get a proper right angle on the tape to ensure the insulated board sits snugly in?

Some of the air tightness tapes out there have the angle already in them to help with their application into corners.

BryanF

rockabaloo wrote: »

Is this true? Can you not just seal the tape to the blockwork and then get the plasterer to plaster over it? Would it be ok to do it this way?

Best to seek advice from the tape manufacture - i'd generally spec the siga perforate tape - fixed to smooth concrete coat, then tape, then plaster over - otherwise your reliant on the top layer of concrete to fully adhere to the tape which isnt fixed very well to the block - there are other methods and products though

rockabaloo

Even if the bond between the tape and blockwork lessened over time would it not be ok by that point because the tape would be completely covered in plaster?

esox28

http://www.boards.ie/vbulletin/showpost.php?p=86667844&postcount=9

Have a look here shows taped reviels plastered into block work ready for plaster boarding.

rockabaloo

Yours looks like good tidy work esox28. I like it. My problem is I'm not using plasterboard round the reveals.

My plan for the windows (at the minute but subject to change if I'm told it won't work):

1) Use Contega FC tape to seal frame of window to blockwork of reveal. I'm gonna use Orcon F on the blockwork to ensure the seal between the tape and the blockwork is a good one.

2) Get the plasterer to plaster the reveals as normal so the tape will end up covered in plaster.

No more air leakage. Will this not work?

esox28

Just from my own experience, not expert but my plasterer and I came to the conclusion that the plaster over the cavity wouldn't be strong enough and maybe become 'bost' or have that hollow sound when you knock on it. I have stone on some of the wall so the full cavity needed to be plastered from internal block 150mm, wouldn't have held that distance, but maybe over 100mm would be ok.

Maybe over 3 passes of plaster one bonding then sand cement and final skim you will cover the distance.
Not a expert just to say again.

rockabaloo

Ah. I see. My cavities have been closed off with block you see. That's why I'm able to tape directly to them and plaster onto that.

I take it the cavities at your windows are closed with cavity closers or something like that?

esox28

Yea full fill cavity insulation.

BryanF

rockabaloo wrote: »

My cavities have been closed off with block you see.

any chance of a detail of how this was done? is this a new house? is your certifier aware of this?

rockabaloo

This is the way the cavity is closed.

rockabaloo

BryanF wrote: »

any chance of a detail of how this was done? is this a new house? is your certifier aware of this?

Is this bad?