How to Prep a Wall for an Airtight Coating
The difference between an airtight coating that lasts and one that lifts is almost always the prep. Get the surface right and the membrane does the rest; rush it and you risk adhesion failure right where it matters.
Why prep makes or breaks the seal
Dust, weak surfaces, open gaps and unsealed penetrations all undermine a membrane — no coating bonds well to a poorly prepared wall. On an airtight layer, a bond failure isn’t just cosmetic; it becomes a leak path on the pressure test.
The five steps of good prep
- Clean: remove dust, grease and loose material
- Make good: pre-fill large gaps and repair friable areas
- Prime: Lime Prime for porous/lime substrates, Primer I.M for dense/smooth ones
- Detail: tape frames and board joints, seal penetrations and junctions
- Coat: apply the membrane to a sound, consistent surface
The solution: the Preparation Pack
The Passive Purple Preparation Pack gathers the membranes, tapes and sealants needed to prepare and detail a wall so your airtight coating bonds cleanly and performs — tape for frames and board joints, sealant for gaps, membrane for the surface.
Benefits
- Everything to prep and detail in one pack
- Better adhesion and a better air test
- The right tool for each part of the job
Frequently asked questions
Which primer do I need? Porous or lime walls: Lime Prime. Dense or smooth: Primer I.M.
Can I skip priming? Only on sound, suitable substrates — when in doubt, prime.
Then follow How to Make a Building Airtight.