Airtight and on show: Airtight White as the finished surface
Nearly every airtightness layer is designed to be covered. It goes on, it gets checked, and then a lining goes over it and nobody sees it again. That is fine until the space in question is one where the structure is meant to stay visible — a car park, a stairwell, a plant room, a museum.
The usual answer is to put an airtight layer on and then build a finish in front of it: two layers, two trades, two programmes, and a void between them. The other answer is to make the airtightness layer the finish.
What you are looking at
Concrete panel walls, coated in Airtight White. There is no lining in front of it and none coming. The white surface in the tour is simultaneously the air barrier, the vapour control layer and the decoration.
Pan around and the thing to notice is how ordinary it looks. No lap lines, no fixings, no board joints telegraphing through — because there are no boards. The coating follows the panel, including the joints between panels, which on this kind of build-up is exactly where the leakage would otherwise be.
What that removes from the build-up
- A trade. No lining means no framing, boarding, taping or skimming in front of the air barrier.
- A void. The continuous cavity behind a dry lining is a leakage path of its own, and a fire and acoustic question besides. There isn't one.
- A thickness. In a space where floor area is the product — a gallery, a plant room, a car park bay — giving back the depth of a lining is not a small thing.
- A risk. An air barrier you can see is an air barrier a facilities team can inspect and repair. Most are sealed behind plasterboard within a week of being installed.
The practical conditions
Two things matter if you want this to look right as well as perform.
Prime it. Airtight White is specified with IM Primer where it is going to be left on show or painted over. On an absorbent or mixed background the primer is what stops the coating being pulled into the substrate and gives you an even finish rather than a patchy one.
Detail before you coat. Panel joints, junctions and penetrations get brush grade first. The field coat goes over the top, and the two cure as one material. The sequence is the same as on any liquid airtight layer — it is just that here the second coat is also the last coat.
Why white, specifically
Airtight White is the white-pigmented version of the same formulation as Passive Purple, so the performance data carries across: Passivhaus certified class A, air permeability 0.02 (±0.002) m³/(hm²) at 50 Pa to EN 12114, watertight to EN 14891, and a radon diffusion coefficient of 3.3 × 10⁻¹² m²/s to ISO/TS 11665-13.
For a space people occupy, the emissions data is the part worth reading: a French A+ indoor-air rating and Finnish M1 class, both for very low VOC emissions. It is VOC-free and water-based, which is also why it can be sprayed in an enclosed space without a programme built around fumes.
Full test data is on Tested & Certified.
Where this gets specified
Car parks, stairwells, plant rooms, stores, basements and exhibition spaces — anywhere the concrete or blockwork was always going to stay visible, and the question was only ever what goes on it. Reuben College, Oxford used Airtight White on an award-winning airtight basement.
If you want the written version of the argument rather than the pictures, start with an airtight vapour control layer you can leave on show. There are more tours of it in the 360° site tours collection.
Got a space where the structure stays visible? Tell us the substrate and the finish you want.