Green Building Forum - Expanding Foam or Tape around new windows?

Expanding Foam or Tape around new windows?

djh — Wed, 01 Oct 2025 21:00:32 +0100

Depends whether the Compriband is UV-stabilised or not, I believe. In any event look at the specific product's instructions to determine whether it can or should be covered.

Expanding Foam or Tape around new windows?

PeterStarck — Thu, 02 Oct 2025 07:50:27 +0100

Posted By: djhDepends whether the Compriband is UV-stabilised or not, I believe. In any event look at the specific product's instructions to determine whether it can or should be covered.

True Compriband is UV stable, other expanding foam tapes may not be.

https://compriband-tape.co.uk/compriband-tape-faqs/

Expanding Foam or Tape around new windows?

djh — Thu, 02 Oct 2025 10:29:54 +0100

Posted By: PeterStarck
Posted By: djhDepends whether the Compriband is UV-stabilised or not, I believe. In any event look at the specific product's instructions to determine whether it can or should be covered.

True Compriband is UV stable, other expanding foam tapes may not be.

https://compriband-tape.co.uk/compriband-tape-faqs/

From the TP450 instructions downloadable from that site:

"For applications where the TP450 will exceed 30 mm
thickness in service, the face of the tape should be covered
using a suitable cover trim to improve the aesthetics and
provide UV protection to the exposed tape surface."

Expanding Foam or Tape around new windows?

PeterStarck — Thu, 02 Oct 2025 16:59:29 +0100

Posted By: djh
Posted By: PeterStarck
Posted By: djhDepends whether the Compriband is UV-stabilised or not, I believe. In any event look at the specific product's instructions to determine whether it can or should be covered.

True Compriband is UV stable, other expanding foam tapes may not be.

https://compriband-tape.co.uk/compriband-tape-faqs/
From the TP450 instructions downloadable from that site:

"For applications where the TP450 will exceed 30 mm
thickness in service, the face of the tape should be covered
using a suitable cover trim to improve the aesthetics and
provide UV protection to the exposed tape surface."

I hope I never have a 30mm gap around a new window

Expanding Foam or Tape around new windows?

revor — Thu, 02 Oct 2025 17:14:56 +0100

To add to my post of over 2 years ago I have had to replace sections of my compriband. After 6/7 years,In places it had come away the adhesion having "failed" and tape consequently blown outward. It had also crazed over in places. As mentioned previously do not use this as your primary seal look at it as a decoratice/neat finish to a backing sealant. Behind my window joints the seal is either EPDM or silicon on backing rod
I had a contractor here a while ago and he does not use compriband but ISO bloco 600 stating this is superior (in what way I did not ask) and there was a wider choice of sizes.
I was going to use this but was not readily availabel when I needed it but a quick look just now and it seems more outlets selling it.

Expanding Foam or Tape around new windows?

fostertom — Thu, 02 Oct 2025 17:49:07 +0100

Posted By: revorIn places it had come away the adhesion having "failed" and tape consequently blown outward. It had also crazed over in places

Would that be because it was exposed to UV and weather?

Expanding Foam or Tape around new windows?

revor — Thu, 02 Oct 2025 18:01:50 +0100

Posted By: fostertomWould that be because it was exposed to UV and weather?

Very probably. Certainly the weather.

Expanding Foam or Tape around new windows?

djh — Thu, 02 Oct 2025 20:35:25 +0100

Posted By: fostertom
Posted By: revorIn places it had come away the adhesion having "failed" and tape consequently blown outward. It had also crazed over in places
Would that be because it was exposed to UV and weather?

I'm curious. Is/was the Compriband the only airtight barrier, or was there another ('proper'?) barrier made of airtightness tape and/or membranes, plaster etc elsewhere through the thickness?

I can easily see how if there wasn't another barrier there would be significant pressure differences that might physically blow the Compriband out, but if there was another barrier I'm surprised that it was blown out.

Expanding Foam or Tape around new windows?

PeterStarck — Fri, 03 Oct 2025 08:19:09 +0100

I'm very suprised that Compriband can be blown out by the weather. When the windows were fitted in my self build, the Compriband was fitted in a central channel running around the whole frame. I added another strip of Compriband between the existing Compriband and the front of the frame which was then covered by the reveal board. The Compriband must be of the correct thickness for it to be airtight and waterproof. If it expands beyond the the specified limit then it loses those qualities.

Expanding Foam or Tape around new windows?

fostertom — Fri, 03 Oct 2025 09:12:07 +0100

To anyone who's uninstalled the stuff, where one of the surfaces was really rough, like roughcast render, can you see whether the strip really expands to seal into such surface irregularities?

Expanding Foam or Tape around new windows?

revor — Fri, 03 Oct 2025 09:44:49 +0100

Posted By: djhI'm curious. Is/was the Compriband the only airtight barrier, or was there another ('proper'?) barrier made of airtightness tape and/or membranes, plaster etc elsewhere through the thickness?

I can easily see how if there wasn't another barrier there would be significant pressure differences that might physically blow the Compriband out, but if there was another barrier I'm surprised that it was blown out.

The windows are in a steel framed structure. They are wooden frames with glazed aluminium framed inserts. They form a 3 sided facade to an atrium. The wooden frames and aluminium sashes were separated so as to affix the wood frames to the steel section with HD brackets. EPDM is bonded to the steel and wood frame. Where the wood frame meets another wood frame the gap is smaller and that gap is closed with backing rod of appropriate size with silicon on top. When the sashes are fixed they are proud of the steel frame and folded aluminium trims are made to measure to cover the gaps and fitted flush with the window. They are fixed to the frame with s/s screws through a small flange on the trims. The gaps between the aluminium trims are then filled with compriband tape to form a neat finish. So all it does is cover the screws. On the inside behind the EPDM and gaps between wood frame and steel is filled with expanding foam. Then plaster-boarded over using fire rated board.
So you will see the compriband has really been pushed out by failure of the adhesion, and exposure to a few years of weather. No air from inside should get through. I also suspect I had some dodgy tape as found with some rolls it had an inherent twist which would not have helped.

Expanding Foam or Tape around new windows?

djh — Fri, 03 Oct 2025 10:23:10 +0100

I'm sorry but your description leaves me very confused. A drawing would likely help. I don't see any mention of where the primary airtightness barrier was? Lots of description of hard materials that need the junctions between them made airtight somehow.

Expanding Foam or Tape around new windows?

revor — Fri, 03 Oct 2025 10:54:40 +0100

Posted By: djhthe primary airtightness barrier was?

That will be the EPDM and the weatherseals between the aluminium framed glazing and the timber frame.

I'll see if can lay hands on a crossection or sketch or draw one for you.

Being airtight is not a consideration for this structure it is an add on to the house. It is airtight in that in winter howling gales there is no perceivable air movement. Between the atrium and the house are DG doors which form the air seal. The atrium is great for collecing solar gain can get really hot in there, in depth of winter sunshine we open house up to it for the heat. Summertime we open roof window and entry doors to cool. The MVHR is not ducted into there.

Expanding Foam or Tape around new windows?

revor — Sat, 04 Oct 2025 10:43:45 +0100

Posted By: djhA drawing would likely help.

Appended an example of how I used the EPDM. This is a corner detail but other steels similar but not as complicated. Not shown is the backing rod and silicon behind the EPDM. I think it was option A I used in the end.The hexagonal hatching is insulation I have added by pen where the compriband goes. You will note the compriband does not offer any weather proofing. Where marked Ali face that is the front of the glazing rame the DG uniits have weather sealing which fit in the timber rebate of the frame profile. Interior finish not shown.

Expanding Foam or Tape around new windows?

djh — Sat, 04 Oct 2025 20:56:47 +0100

Thanks for that. I take it the diagonally striped rectangle is timber, and the three thin rectangles are a steel I-beam seen end-on? Looking at the lower Compriband in drawing A, what is the white rectangle above it and the vertically striped area to the immediate right? How is the EPDM fixed?

Expanding Foam or Tape around new windows?

revor — Sun, 05 Oct 2025 10:05:28 +0100

Posted By: djhI take it the diagonally striped rectangle is timber,

Correct to allow furthe fixings internally

Posted By: djhand the three thin rectangles are a steel I-beam seen end-on?

Yes H on its side cross section through vertical pillar.

Posted By: djhwhat is the white rectangle above it and the vertically striped area to the immediate right?

Cross section through the window frame in which the glazed sash fits and lock in place with special hardware,
The stripes illustrate packers.

Posted By: djhHow is the EPDM fixed?

It is fixed with a special bitumen sealant/adhesive comes in an aluminium thin tube (sausage)that fits in a large diameter sealant gun that is a tube into which the sausage fits and which collapses as the plunger moves down the tube to dispense the adhesive. The stuff sticks to almost anything but brick concrete and similar needs a special primer..You can find more detail here whose products I used.

https://www.arbo.co.uk/

Expanding Foam or Tape around new windows?

djh — Sun, 05 Oct 2025 12:29:53 +0100

Thanks again. So it seems to me that the packers aren't airtight and the EPDM is flexible, so the EPDM must have pushed the Compriband out after the Compriband's adhesive failed. I can't see what else would have caused it to be ejected from the gap.

I remember that with airtightness tapes it is necessary to go over them after installation, pressing them into place with the back of a knife or similar. That's necessary to make sure the glue is properly stuck. I can't see how its possible to apply that kind of pressure to Compriband in most situation, so I'm not terribly surprised that its adhesion fails after a while. But as long as there's no pressure differential across it, its own elasticity will keep it in place. At least, that's my best guess.

Expanding Foam or Tape around new windows?

revor — Sun, 05 Oct 2025 13:23:46 +0100

Posted By: djhThanks again. So it seems to me that the packers aren't airtight and the EPDM is flexible, so the EPDM must have pushed the Compriband out after the Compriband's adhesive failed. I can't see what else would have caused it to be ejected from the gap.

I remember that with airtightness tapes it is necessary to go over them after installation, pressing them into place with the back of a knife or similar. That's necessary to make sure the glue is properly stuck. I can't see how its possible to apply that kind of pressure to Compriband in most situation, so I'm not terribly surprised that its adhesion fails after a while. But as long as there's no pressure differential across it, its own elasticity will keep it in place. At least, that's my best guess.

The tape's natural inclination is to expand. When its adhesive properties fail then it wants to expand. Ideally the tape should have adhesive on both surfaces. When putting the tape in place you have to make sure that both sides are in contact with the sides of the gap being filled otherwise it will expand outward starting from the non adhesive side. When putting in, the tape is shosen so that it easily goes in the gap but also that you do not exceed the recommended width of the tape on expanion. When in place you can press the adhesive side with a spatula knife. Best to on a cool day so you have time to put it in particularly on a long length.

Expanding Foam or Tape around new windows?

wookey — Fri, 10 Oct 2025 17:05:43 +0100

Internorm (when mounting into an outer leaf with internal plaster airtightness layer) use illbruck FM330 foam designed for window/air-tightness sealing (remains flexible) and tescon profil airtightness tape (and 2 thin stainless mounts on the sides for rigidity). This seems to me to be a very way to get reliably good airtightness. It's 3-4 times the cost of cheapo foam, but good stuff, and this is negligible in comparison to the window cost.

Expanding Foam or Tape around new windows?

djh — Fri, 10 Oct 2025 21:03:05 +0100

Sounds like FM330 is a competitor to Soudal's Soudafoam?