Vapour-Open External Airtightness for Retrofit (Brush)
Retrofitting airtightness onto a solid or older wall is tricky: you need to stop air and weather getting in without trapping moisture in the structure. That calls for a vapour-open, fire-rated membrane applied where it works hardest — the details.
The problem with sealing old walls
Many external coatings seal so tightly they trap moisture in solid walls, risking damp, decay and interstitial condensation. Retrofit guidance such as PAS 2035 puts moisture safety front and centre — so any airtight upgrade to an existing wall must let the structure breathe.
The solution: Passive Purple X (5kg Brush)
Passive Purple X (5kg) is a brush-applied, vapour-open airtight membrane with a Class B fire rating. It lets walls breathe while sealing them against air and weather — ideal for retrofit detailing on solid walls, around openings and at junctions.
How it is applied
- Prepare and, where needed, prime the existing substrate
- Brush the membrane into reveals, junctions and penetrations
- Tie into the wider retrofit airtight strategy
Benefits
- Vapour-open — walls can still breathe
- Class B fire rating
- Brush-applied for retrofit detailing
Frequently asked questions
Why vapour-open for retrofit? Solid walls need to dry; a vapour-open membrane stops air and rain without trapping moisture inside.
Brush or spray? Brush for details; use the spray grade for large external areas.
Planning a retrofit? See How to Retrofit Vapour Control Without the Mess.