Airtightness solutions — Passive Purple liquid airtight membrane paint for passing air tests, Part L and Passivhaus

Internal

Internal airtightness and vapour control in one liquid system. The internal face of your walls and roof is where the airtight line lives — and where most air tests are won or lost. Our liquid-applied vapour control layer (VCL) replaces sheets, laps and tapes-everywhere with one seamless airtight coat.

🔗 One coat, both jobs. Passive Purple is the airtight layer and the vapour control layer in a single membrane. Here about condensation, damp or “do I need a VCL?” rather than an air test? Read the vapour control side.

The internal airtight system

  • Bulk areas — Passive Purple spray or roller applied: airtight, smoke-tight vapour control paint, Passivhaus certified and BBA approved.
  • Junctions & penetrations — Passive Purple brush grade worked into corners, joist ends and service penetrations.
  • Frames & board joints — IM Fleece Tape, plasterable and vapour-open.
  • Gaps & movement joints — Passivhaus airtight sealant.
  • On-show finishes — Airtight White: the same membrane in VOC-free white, smart enough to leave exposed or paint over.

Explore the full VCL membrane collection and airtight paint range.

Why it beats sheet VCLs

A liquid VCL can’t be torn, stapled through or left flapping at a lap joint. It bonds to blockwork, concrete, timber, OSB and plasterboard, cures flexible so it moves with the building, and the purple (or white) finish makes quality control visual — if it’s coated, it’s sealed. Plaster and dot-and-dab go straight over it with Supergrip primer.

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