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 inside face of your walls and roof is where the airtight line lives, and it’s where most air tests are won or lost. Instead of sheets, laps and tape everywhere, our liquid-applied vapour control layer (VCL) goes on as one seamless airtight coat.

🔗 One coat, both jobs. Passive Purple is the airtight layer and the vapour control layer in a single membrane. More worried about condensation, damp or “do I need a VCL?” 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, so if it’s coated, it’s sealed. Plaster and dot-and-dab go straight over it with Supergrip primer.

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