Sealing Junctions and Penetrations with Brush-Applied Airtight Paint
Most air leakage doesn’t happen across open walls — it happens at the junctions, corners and service penetrations where details get fiddly. That’s exactly where a brush-applied airtight membrane earns its keep.
Why details decide the air test
Sprayed membranes are fast on flat areas but awkward around pipes, cables, corners and wall-to-floor junctions. These transitions are where air finds its way through — and where pressure tests are won or lost. Detailing them properly is the difference between hitting and missing your Part L target.
The solution: Passive Purple Brush
Passive Purple Brush (6.9kg) is a fibre-reinforced, brush-applied airtight vapour control membrane. It spans gaps and seals tricky junctions and penetrations by hand, working alongside sprayed Passive Purple on the open areas — the right tool for each part of the build.
Where to use it
- Wall-to-floor and wall-to-ceiling junctions
- Around pipes, cables and soil stacks
- Window and door reveals
- Cracks and gaps a sprayer can’t reach cleanly
Benefits
- Fibre-reinforced — spans gaps
- Ideal for junctions and penetrations
- Passivhaus-certified airtight membrane
Frequently asked questions
Can I use only the brush grade? On small jobs, yes; on larger areas, brush the details and spray the open faces.
Can it be plastered over? Yes — prime with Supergrip first for a strong key.
See the full method in How to Make a Building Airtight.