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FAQ

❓ Liquid-Applied Membranes — Main FAQ (Airtightness & Waterproofing)

At Intelligent Membranes, we help architects, contractors, retrofitters and self-builders achieve airtightness and waterproofing targets with liquid-applied systems.
Our flagship airtight system, Passive Purple®, is airtight at all times yet breathable when the building fabric needs to release vapour — we call this intelligent breathability.

Explore the range:
Passive Purple External • Passive Purple (Internal) • Airtight White • Goat Waterproof Membrane (Bathrooms/Wetrooms) • IM Primer • Lime Prime • Services / Installation • Contact Technical

General: Airtightness vs Waterproofing

What’s the difference between airtightness and waterproofing?

What does “intelligent breathability” mean?
The airtight layer stays airtight, yet is vapour-open when needed, letting moisture diffuse out of the structure. This balance reduces condensation risk — crucial in retrofit and timber frame projects. See Passive Purple External and Passive Purple (Internal).

Can an airtight product replace a waterproofing membrane?
No. Airtight products manage air and vapour; waterproofing membranes manage water. For wetrooms, choose Goat Waterproof Membrane; for roofs, contact Technical.

Internal Airtightness (Passive Purple® Internal, Airtight White)

Where do I use internal airtight paint?
On the warm side of the envelope as the continuous air barrier behind finishes — ideal for retrofit and new build. Start with Passive Purple (Internal).

What is Airtight White?
A finished internal airtight paint providing a clean white aesthetic while maintaining the airtight layer. Use alone (where suitable) or over Passive Purple Internal. See Airtight White.

Do I need a primer?
Often yes. Use IM Primer for general porous/dusty substrates and Lime Prime on lime-based surfaces.

How is it applied?
Spray for fast coverage; roller/brush for details. Apply the first coat, detail penetrations/frames, then the second coat to reach the required dry film thickness. If you’d like help on site, book our Services / Installation.

How do I verify performance?
Via airtightness testing (e.g., blower door) and site checks for continuity and dry film thickness. For support, Contact Technical.

External Airtightness / Weather Barrier (Passive Purple® External)

What is Passive Purple External for?
A Class B fire-rated, smoke-tight, vapour-open airtight paint used as an external weather/air barrier (also suitable internally where fire and drying performance are priorities). See Passive Purple External.

Is it “breathable”?
Yes — intelligent breathability: airtight against leaks, vapour-open when the structure needs to dry. Compare with Passive Purple (Internal).

Where does it shine?
Timber frame, retrofit, exposed elevations and details where you want a robust air barrier that still lets the structure dry. For installation help, see Services.

What about fire and compliance?
EN 13501-1 Class B and smoke-tight. For certificates and guidance, Contact Technical.

Bathroom & Wetroom Waterproofing

What does a bathroom/wetroom membrane do?
It creates a waterproof tanking layer on walls, floors, showers and niches so water can’t penetrate. Use Poseidon.

Is it compatible with tiling?
Yes — once cured per the TDS, it can be tiled over with suitable adhesive. For product specifics, see Poseidon

How do I handle corners and penetrations?
Reinforce corners, upstands and joints as specified, and seal valves/pipework with compatible sealants. Need detailing advice? Contact Technical.

Roofing Waterproofing (Liquid Systems)

When do I use a liquid roofing membrane?
For flat roofs, balconies and terraces, or to overlay certain existing roofs to form a seamless waterproof layer. For system selection and specification, Contact Technical.

Which substrates are typical?
Concrete, screeds, timber decks and some existing systems — all clean, dry, sound and properly primed. For site support, see Services / Installation.

Primers, Accessories & Detailing

Which primer should I use?

  • IM Primer — general purpose on porous/dusty surfaces.
  • Lime Prime — lime plasters or lime substrates.

What helps maintain continuity?
Use sealant tubes / liquid grommet equivalents at services and tricky junctions, and include reinforced details where specified. Browse accessories in the Shop or Contact Technical.

Common Questions Across All Systems

Will airtight paint trap moisture?
Not with Passive Purple’s intelligent breathability — it stays airtight yet is vapour-open when needed. See Passive Purple External and Passive Purple (Internal).

How many coats do I need?
Usually, two to reach the specified dry film thickness (follow each product’s TDS). For on-site guidance, book Services / Installation.

Where can I get documentation?
Technical data sheets, safety data and installation guides are available via Contact Technical.

Who is this for?
Architects/specifiers, main contractors/installers, retrofit teams and self-builders aiming for airtightness, moisture safety and durable waterproofing.

How do I get help or book a CPD?
Speak to the Technical Team for specs and detailing, or request a CPD via Services.

Quick chooser: which system do I need?

Optional extras to paste below the FAQ (nice SEO boosts)

Add a small CTA row: Contact Technical • Services / Installation • Shop

Link to case studies or blogs that show real installs: Blog