Priming Porous and Lime Substrates Before Airtight Coatings
On porous, dusty or lime-based walls, even the best liquid membrane can struggle to bond — and poor adhesion is the quickest route to a failed air test or a peeling coating. The fix is the right primer.
Why porous and lime substrates are tricky
Lime plaster, old masonry, AAC blockwork and other porous substrates pull moisture out of a coating as it cures and leave a dusty, friable surface that membranes can’t grip reliably. Skip priming and you risk pinholing, poor adhesion and a membrane that lifts — exactly what you don’t want in an airtight layer.
The solution: Lime Prime
Lime Prime is a primer formulated to stabilise and bind porous and lime substrates, consolidating dust and regulating absorption so membranes like Passive Purple and Airtight White bond to a sound, consistent surface.
How it is applied
- Remove loose material and dust from the substrate
- Apply Lime Prime and allow it to penetrate and cure
- Apply your airtight or vapour control membrane over the primed surface
Benefits
- Binds dusty, porous and lime surfaces
- Regulates absorption for an even cure
- Improves membrane adhesion and durability
Frequently asked questions
When do I need a primer? Whenever the substrate is porous, dusty, friable or lime-based. On dense, smooth surfaces, use Primer I.M instead.
Does it affect breathability? It’s designed to work within breathable build-ups — check the datasheet for your specific system.
Working on a retrofit? See How to Retrofit Vapour Control Without the Mess.