Compression Tape:
When I asked a prospective installer of new (replacement) double-glazed windows about use of compression tape around the sides, he was interested, appeared prepared to consider it and noted that on the written quote - tho he said he hadn’t heard of it before, his firm (Malbern) haven’t been using it. He mentioned the more-standard sealants and expander foam, etc.
It’s presumably worth my while pressing this point… How much of an improvement does compression tape give? Is the clearance between window-frame and aperture substantially different, compared to the sealant etc methods? (Malbern manufacture their own window assemblies.)
Preventing Spillage of Cavity Insulation:
I also raised ‘cavity closers’, to prevent the insulation beads recently installed in the cavity from spilling out… He said they’d ensure that was addressed and wrote it on the quote, however I’m actually quite worried about that, as any spillage could result in cold patches.
Thanks folks,
Mike Killian
Proper taping gives an airtight fit. Foam and trim don’t. If the use foam against your wishes you can rescue the situation with Blowerproof.
I would hope the beads were coated in a slow cure adhesive. Check with the installer if your contract is unclear. If not, and there aren’t cavity closers already in place, you could be up s**t creek without a paddle. It becomes a three man job to remove the old window and you will still loose some of the insulation.
(Keep any insulation that escapes and refill the top of the cavity as the insulation settles to its new level.)
Ok, thanks Tim. I’ll push the windows-installers to use tape, eg Iso-Chemie, or Illbruck products.
The CWI paperwork says, ‘…EPS beads are coated with a bonding adhesive… to bond and set the EPS beads and to make the bead-fill stable…’ - which the installer demonstrated for me at the time. I’ve emailed the main guy who directed the job (from the office) to ask for clarification. I’ll also get back to the windows-quoters, for more detail on how they address CWI.
…actually had a good chat with the CWI main man, who rang me up to discuss what can be done about the question of retaining your CWI during window-installation, how they could help afterwards if necessary etc, so that’s good. (I didn’t press him on charges, at this point.) And the windows people themselves say, Yes we do use compression tape, mostly on new-builds where walls are still square!, but willing to do so if that’s what we want, etc.
Hi,
I would insist on the compression tape being applied as the sealants etc can degrade , shrink and move. Here are some numbers from Vitaseal that should help-
Compression protection values from uncompressed to 75% compressed:
0% no compression - Protects against the ingress of Dirt, Leaves + Insects.
30% compressed - Air flow, Dust + all the above values.
50% compressed - Thermal loss, Acoustic transmission, + all the above values.
75% compressed - Driving rain, + all the above values.
Thanks Lloyd - so, as a test for your 50% level that insulates thermally, I’m basically looking for the tape to be at least 50% compressed, ie less than half the thickness of what a short piece of tape left aside on a nearby table-top would expand to?
On others’ helpful advice, I’m further considering cutting-back mortar/plaster about a cm behind/inside the newly-fitted window-frame, then airtight-taping the frame to the exposed brickwork, then re-instating mortar/plaster to back of frame, ie overlapping the airtight-tape. Good plan…?
I am wondering whether compression tape alters over time to a fixed size, dependent on its compression, or whether it remains flexible, changing its form to allow for changes in the gap between window frame and reveal. The latter could be particularly useful for timber structures with change in humidity or materials with highly differing coefficients of expansion.
Correct. I have painted liquid brush-on Blowerproof from frame to brick for all my windows apart from the kitchen, which is awaiting more extensive, unrelated, work, at which point I’ll do there too.
At the bottom that includes frame to sill to foam to brick.
Well today was installation of three new double-glazed windows (PVC - yes, I know…) However instead of the agreed compression tape, the installers turned up with a couple of rolls of Screwfix draught-excluder. (NB it’s not the two installers’ fault.) I had to let the installation of window #1 be completed with standard squirty expander-foam; I’ll rescue that later with either Blowerproof or Contega Solido Exo airtightness tape (that I’ve been using to insulate/block/seal the cavities directly under the windowsills.) There followed a lengthy phone discussion with a higher-up who agreed to supply the compression below (which he unearthed while we haggled.) So the job is now postponed for three days so the other two windows can be done as agreed. 2-6 Expanding Foam Tape Seals Gaps between 2mm and 6mm (affixit.co.uk)
Eventually, Window #2 and Window #3 went in properly; I’m rescuing Window #1 with a combination of measures; I’m nearly done airtight-taping all 3, and I’ve blocked -off and airtight-taped the cavities under the 3 windowsills. So, definitely worth specifying how the window-installation is to be done, and then checking that it is being done.
Well done for insisting and checking. Why is this so difficult to do right for window installers?!
You put a new window in and leave an obvious gap between the frame and the reveal… don’t they just feel bad for such a job?
Anyway, I believe expanding spray foam should last for a similar time as the window and should also be able to create an airtight seal, but is less controlled when being applied.
I am now considering to ask for specific expanding tape and also ask from the installers to take pictures to proof everything is sealed. I am even happy to pay a little extra time for that and get it done properly (although I think this should be standard).
Are there any recommendations about tape or foam to be used?
Also, did you have any vapour control membranes in the wall that you sealed with the window frame or did you use plaster?
How have your windows been faring this winter? Hope all is good!
Expanding spray foam is not airtight. It forms enough of a baffle for humans not to detect air movement but if you rely on it in a lot of locations (eg around all windows and penetrations) you WILL get a measurable air movement.
Compression tape remains flexible after installation, adjusting to movement of the building’s fabric. Spray foam becomes rigid and crumbles when later shifting occurs.
I used Blowerproof as a way to overcome the failings of foam. Similar products can be used, or if you prefer airtightness tape use that after the foam has cured.
There are specific airtight expanding foams. I always have a box of 24 on site. Always great to have at hand. Such as illibruck FM330
As is always the case, the best jobs have layers of protection at weak points.
The phyical airtight membrane/tape that connects the window frame to the plaster airtight envelope. This is the most important. Make sure this is in place.
Then spraying in FM330. The previously installed tape stops the stuff goin all over the inside fo your house. And ensures no air pockets. This foam will expand and also act as an insulant. It is flexible and will not harden.
Finish off however, with foam tape such as compriband is great, even better bring EWI over the frame. Some people add a trim of some kind, not as good.
If you have IWI then of course it should butt up to the frame, and your airtight layer is on the inside.