Priming Dense Substrates Before Airtight Membranes
Not every wall is porous — some are too dense or too smooth for a membrane to key into. On those substrates, the right primer is what makes the coating stick and stay stuck.
The problem
Dense concrete, power-floated slabs, smooth render and similar surfaces give a membrane very little to grip. Without a key, even a good airtight coating can delaminate under stress or fail to develop full adhesion — a hidden risk in the airtight layer.
The solution: Primer I.M
Primer I.M strengthens and keys dense substrates, giving membranes like Passive Purple a sound surface to bond to. For porous and lime walls, use Lime Prime instead — the two cover the full range of substrates between them.
How it is applied
- Clean the surface of dust, laitance and contaminants
- Apply Primer I.M to create a key
- Apply the membrane once the primer is ready
Benefits
- Improves adhesion on dense, smooth surfaces
- Strengthens the substrate
- A more reliable, longer-lasting membrane
Frequently asked questions
Dense or porous — which primer? Primer I.M for dense/smooth; Lime Prime for porous/lime/dusty.
Do I always need a primer? Not always — but on marginal substrates it’s cheap insurance against adhesion failure.
Read Priming Porous & Lime Substrates for the other half of the picture.