Airtightness Tape vs Liquid Airtight Membrane
Airtightness tape and a liquid airtight membrane solve different parts of the same problem: maintaining a continuous air barrier across the building envelope. Tape provides a strip connection; a liquid product forms a coating over its prepared substrate. The right choice depends on the detail and the working sequence.
A useful specification may include both. Rather than pricing one roll against one tub, map the surfaces and junctions that need sealing and decide how each connection will be built, checked and protected.
Where tape fits the job
Consider tape for a defined connection where its full bonding area is accessible: for example, a specified transition between a window frame and adjoining construction. The strip gives the installer a visible route to follow and a clear edge to inspect.
For a fleece-faced tape, the surrounding finish also matters. Check the actual tape's technical information, the bonding surfaces and the finishing detail. Our airtightness tape guide explains these selection questions, and the IM Fleece Tape page provides current product documentation.
Tape can become awkward when access restricts pressing, the joint changes direction repeatedly or the available landing is too narrow. Those are reasons to revisit the design before installation. They do not disappear simply because the adhesive feels strong.
Where a liquid membrane fits the job
A liquid approach is worth considering where the air barrier needs to cover an area of substrate or follow a complex surface. Passive Purple Internal is available as a spray or roller-applied coating; a separate brush-applied version is intended for detailing. The products have their own instructions and should not be treated as interchangeable consistencies of ordinary paint.
The Passive Purple Internal technical sheet requires preparation of the substrate and closure of holes and joints before coating. It specifies application in layers and verification of coating thickness. A visible colour change alone is therefore not a sufficient quality check.
At quotation stage, identify masking, access, drying periods and protection from following trades. A large clear wall and a small occupied room with many finished surfaces present different working conditions, even if the measured wall area is identical.
Compare complete installation costs
| Question | Tape detail | Liquid detail |
|---|---|---|
| What is measured? | Connection length, required width, corners and overlaps | Area, specified consumption and separate detailing |
| What preparation is needed? | Sound bonding surfaces, cleaning and any approved primer | Sound substrate, gap treatment and any approved primer |
| What must be inspected? | Contact, edges, joints, corners and movement allowance | Coverage, thickness, continuity and drying |
| What follows installation? | The specified compatible finish and protection | The specified drying, finishing and protection sequence |
Use the same drawing to obtain both prices. Ask each installer to identify what is included and what another trade must complete. This makes missing preparation or junction work visible before it becomes a variation on site.
How to combine tape and liquid correctly
Start by drawing the air barrier through a section of the building. Mark each point where it changes material: frame to reveal, wall to floor, wall to roof and around a service. Then assign a written detail to each transition.
Where a coating connects to a tape, confirm compatibility with that exact tape face and the adjoining substrate. Establish the overlap, preparation and finishing requirements with the system supplier. Do not assume that approval to coat one brand of tape covers every fleece or plastic surface.
Record who completes the connection and who inspects it. A well-made strip that stops short of the wall coating still leaves an incomplete route. Photograph the transitions before insulation, linings or finishes obstruct the view.
Keep performance requirements separate
Airtightness, vapour control, weather resistance and ground-gas protection are separate specification questions. The BBA certificate for Passive Purple and Airtight White defines the assessed products and their conditions of use. Use its relevant details and the current installation guidance rather than extending a product claim to an entire unverified assembly.
Similarly, a room becoming less draughty does not establish that the ventilation provision is adequate. Keep the air-barrier work coordinated with the project's ventilation and moisture design.
Common questions
Which option is cheaper?
Compare installed costs for the actual drawing. Length, area, substrate repair, access, corners and finishes can change the balance considerably.
Can liquid membrane repair peeling tape?
A repair needs sound material beneath it and an approved connection detail. Diagnose the failed bond before selecting the covering material.
Can I use both on one project?
Yes, where the specified details establish compatible, continuous connections. Review the Passive Purple airtightness range and send our technical team your drawings to agree how the tape and coating should meet.