Component A
Component A, always, on anything that carries a sash. It is the difference between a callback and a reference.
See specificationWindows and doors
Filling window and door joints that stay sealed
The reveal is where air, water and sound get in — and where a cheap grade shows itself two winters later.
What goes wrong on site
Three failures, in the order they appear
- 01
Openings are never square; the gap varies around the same frame.
- 02
Shrinkage cracks open the paint line in year two.
- 03
Air-tightness and water-tightness tests are failed at the frame, not the glass.
Why one-component foam, and not something else
Three properties, no chemistry
- Mobility: a can and a gun reach a joint that a panel, a board or a truck cannot.
- Irregular geometry: it expands to the shape of the void, including penetrations.
- Closed cell: air barrier and moisture barrier in one pass, without a second trade.
How it is done, and what to hold
The four numbers this job lives on
| Step | What to hold |
|---|---|
| Surface | Joint brushed and misted, wedges and packers removed or protected, frame surface clean. |
| Fill volume | One third of the joint depth. The foam expands to fill; filling it to the top bends frames and wastes material. |
| Passes | Two passes of 30 mm at most. A single thick pass traps heat and collapses in the core. |
| Trim | Cut after the window on the parameter card. Never pull or press uncured foam. |
| Cover | PU is not UV-stable. Any exposed face gets sealant, render or a trim within 48 hours. |
Typical guidance. The parameter card for your grade carries the tolerances your operators work to.
Common failures
Three ways this job goes wrong
- Filling the joint full: the frame bows and the sash stops closing.
- Using an economy grade on a load-bearing frame — the classic year-two callback.
- Trimming while tacky tears the cell structure and opens a water path.
What to tell your customer
Three sentences you can copy into a quotation, a WhatsApp message or a site meeting. Your competitors' websites talk about themselves; this block is for you to talk about the job.
„The joint is filled to one third and left to expand — the frame stays square.“
„Closed-cell foam, class I adhesion, then a vapour-tight tape or sealant.“
„We can show the airtightness test at the frame line, not just the glass.“
Send the drawing or the photo — we will reply with the parameters.
Technology brand
Tell us the joint, the substrate and the season
- 1 tonne minimum, five 200 L drums
- SDS, COA and Form E with every shipment
- We reply within 24 hours, Monday to Saturday.