My Builder Forgot the Vapour Control Layer? Don’t Panic — Here’s How to Fix It

Few things make a builder’s heart sink like realising the vapour control layer has been missed. Hand on head, kettle on — but don’t panic.

A forgotten vapour control layer (VCL) is one of the most common things we get calls about. Because our membranes are liquid-applied, it’s almost always fixable without ripping anything out. The right solution simply depends on how far the build has gone.

First, why it matters

A vapour control layer sits on the warm side of the insulation and limits how much moisture moves into the structure. Skip it and you risk interstitial condensation, mould and reduced insulation performance. So it’s well worth putting right — here’s how.

Option 1: The walls are finished and painted

If you’ve completely finished — plastered and painted — the answer is Airtight White.

It’s a VOC-free, water-based airtight vapour control membrane that dries white, so it blends into the finish. Simply roll or spray it over the existing painted surface, let it dry, and paint straight over the top in your chosen colour. Airtightness restored — no demolition.

Option 2: It’s plasterboarded but not yet plastered

If the boards are up but the skim coat hasn’t gone on, reach for Passive Purple®.

Spray or roll Passive Purple across the boards and junctions to form a continuous airtight layer. Then apply Supergrip — a primer that gives plaster a key to grip to — and you can plaster straight over the top as normal.

Either way, you’re covered

Both routes are retrofit-friendly, seal awkward junctions and penetrations, and get your airtightness back on track without tearing the room apart.

Not sure which option fits your stage of build? Contact us today and we’ll point you to the right product.