Poseidon — Bathroom & Wet Room Waterproof Membrane Paint
Poseidon — Bathroom & Wet Room Waterproof Membrane Paint
Liquid-applied, polymer-based waterproof membrane for bathrooms, wet rooms, showers, steam rooms and any internal high-moisture environment. Seamless, flexible, no corner reinforcements needed. Spray, roller or brush applied. ETA and EPD certified.
What is Poseidon Waterproof Membrane Paint?
Waterproofing before tiling is not optional in wet rooms and shower enclosures — it is required by UK tile industry standards (BS 5385) and is the only reliable way to prevent water ingress behind tiling causing damp, mould, structural damage and failed adhesive bonds. Poseidon forms the continuous waterproof membrane that protects the substrate and keeps everything behind the tiles exactly where it belongs: dry.
Poseidon holds a European Technical Assessment (ETA) and uniquely for a bathroom waterproofing product, also holds an Environmental Product Declaration (EPD) — providing independently verified environmental impact data for use in BREEAM assessments, net-zero specifications and sustainable construction projects.
Why Liquid-Applied Beats Traditional Tanking Systems
Most bathroom waterproofing failures happen at the weak points — corners, joints, pipe penetrations and the edges of sheet membranes. Liquid-applied membranes like Poseidon eliminate these weak points entirely.
❌ Traditional Tanking (Slurry / Sheet)
- Fabric corner tape required at all junctions — each joint is a potential failure point
- Slurry systems can crack if the substrate moves — not flexible
- Sheet membranes require mechanical fixing — every fixing penetrates the waterproof layer
- Difficult to achieve consistent coverage around pipes, outlets and complex geometry
- Cannot be applied over existing tiles — substrate must be stripped back
- Time-consuming — multiple layers plus tape plus primer required
✔ Poseidon Liquid Waterproof Membrane
- No corner tape needed — elastic polymer bridges all junctions and movement
- Flexible formulation accommodates substrate movement without cracking
- Liquid-applied — no fixings, no penetrations, no joints to fail
- Flows around pipes, outlets and complex geometry automatically
- Applied directly over existing tiles — ideal for refurbishment without strip-out
- Brush, roller or spray — fast application on any scale
Key Features of Poseidon Bathroom Waterproofing Membrane
Complete Vapour Barrier
Poseidon provides a complete vapour block that prevents moisture transmission through the substrate — protecting walls, floors and building structure from long-term water damage, damp and mould growth.
No Corner Reinforcements Needed
The elastic polymer formulation bridges all internal angles, corners and movement joints without fabric tape or secondary reinforcement — reducing preparation time and eliminating a major source of waterproofing failures.
Spray, Roller or Brush Applied
Poseidon is fully compatible with airless spray machines for large commercial projects, or applied by roller and brush for domestic bathrooms and wet rooms. This flexibility makes it suitable for any project scale.
Goes Over Existing Tiles
Poseidon bonds directly over existing tile floors and walls — making it ideal for bathroom refurbishments where stripping back to the substrate would be disruptive or impractical. Saves time, cost and waste.
Flexible — Crack Bridging
The polymer formulation is elastic and crack-bridging, accommodating thermal movement and minor substrate cracking without breaking the waterproof seal. Long-term protection even as the building moves.
Steam Room Rated
Formulated for continuous contact with moisture and steam — suitable for steam rooms, spa facilities and saunas as well as standard shower enclosures and wet rooms. Resistant to UV, chemicals and environmental wear.
ETA Certified
Poseidon holds a European Technical Assessment (ETA) — providing independent performance verification and supporting architects and contractors who need certified product documentation for Building Control submissions.
EPD Certified — Unique in Category
Poseidon is one of the very few bathroom waterproofing membranes to hold an Environmental Product Declaration (EPD) — providing independently verified environmental impact data for BREEAM assessments, WELL certifications and net-zero construction projects.
Where to Use Poseidon Waterproof Membrane
Poseidon is designed for all internal high-moisture environments where a reliable, seamless waterproof membrane is required before tiling or finishing. It is not suitable for external applications, basements or areas with standing water pressure.
Compatible Substrates
Poseidon bonds directly to all of the following substrates commonly found in bathroom and wet room construction. Substrates marked with a primer note require a coat of Supergrip Primer before application:
Not suitable for: bitumen or asphalt-based substrates, surfaces with continuous standing water pressure, moving cracks or highly flexible joints, non-compatible coatings.
How to Apply Poseidon — Step by Step
- Prepare the substrateEnsure the surface is clean, sound, dry (or firm-damp for cementitious substrates) and free from dust, grease, loose material and incompatible coatings. Remove any standing water. For smooth, dense or non-porous surfaces, lightly abrade to improve adhesion.
- Prime where requiredFor plaster, gypsum moisture board and Hardie Board, apply one coat of Supergrip Primer and allow to dry fully before applying Poseidon. Priming is not required on concrete, cementitious plaster, plasterboard or existing tiles.
- Apply first coat of PoseidonApply Poseidon evenly by brush, roller or airless spray across the full area. Work carefully into internal angles, corners, pipe penetrations and drainage upstands. Allow the first coat to dry fully before applying the second coat.
- Apply second coatApply the second coat of Poseidon perpendicular to the first, ensuring full coverage with no missed areas. Total recommended dry film thickness: minimum 1mm across the full area. Total consumption typically 1kg per m² across both coats.
- Allow to fully cureKeep the membrane free from water contact until fully cured. Good ventilation accelerates drying. Do not tile until Poseidon is completely dry and has formed a solid, continuous blue membrane across the entire area.
- Tile or finishOnce cured, Poseidon is ready to receive tile adhesive, render or other finishing systems. The cured membrane forms a robust, flexible base for all standard bathroom tile adhesives and fixing systems.
Clean tools and equipment immediately after use with cold water.
Poseidon vs Other Bathroom Waterproofing Methods
| Feature | Poseidon (Liquid Membrane) | Tanking Slurry | Sheet Membrane | Waterproof Board System |
|---|---|---|---|---|
| Seamless — No Joints | ✔ Liquid applied | ✔ Liquid | ✘ Lapped joints | ✘ Board joints |
| No Corner Tape Needed | ✔ Not required | ✘ Required | ✘ Required | ✘ Joint treatment |
| Flexible / Crack Bridging | ✔ Elastic polymer | ✘ Rigid — cracks | Varies | Rigid boards |
| Applied Over Existing Tiles | ✔ Yes | Some products | ✘ Strip-out required | ✘ Strip-out required |
| Spray Application Available | ✔ Yes | ✘ Brush/roller only | ✘ Not applicable | ✘ Not applicable |
| Steam Room Rated | ✔ Yes | Varies | Varies | Varies |
| ETA Certified | ✔ Yes | Varies | Varies | Varies |
| EPD (Environmental Declaration) | ✔ Yes — unique | ✘ Rare | ✘ Rare | ✘ Rare |
| Speed of Application | Fast — spray or roller | Slow — multiple layers | Medium | Slow — board fixing |
Technical Specification
| Property | Detail |
|---|---|
| Product Type | Liquid-applied polymer-based waterproof membrane |
| Application Method | Airless spray machine, roller or brush |
| Available Sizes | 7kg | 10kg | 12kg |
| Colour | Blue |
| Coverage Rate | ~15–20m² per 10kg at 1mm dry film thickness |
| Minimum Thickness | 1mm dry film (recommended for waterproofing performance) |
| Use | Internal use only |
| Flexibility | Elastic, crack-bridging — accommodates building movement |
| Corner Reinforcement | Not required |
| Suitable Environments | Bathrooms, wet rooms, showers, steam rooms, kitchens |
| Resistant to | UV exposure, chemicals, moisture, steam, continuous water contact |
| Certifications | ETA (European Technical Assessment) | EPD (Environmental Product Declaration) |
| Also Available With | Copagro Sealant (for joints and penetrations), Supergrip Primer (for select substrates) |
📄 Download Technical Data Sheet (TDS) | 📄 Download Install Guide | 📄 Download Safety Data Sheet (SDS) | 📄 Download ETA | 📄 Download EPD
Certifications & Documentation
EPD — Environmental Product Declaration
Poseidon is one of very few bathroom waterproofing membranes to hold an independently verified EPD. Essential for BREEAM, WELL and net-zero construction specifications. Download EPD →
ETA — European Technical Assessment
Independent performance verification for use in Building Control submissions and architect specifications. Download ETA →
NBS Specification Clause
Poseidon is listed on the NBS Product Selector — ready-to-paste specification clauses available for architects. Add to NBS Spec →
RIBA Product Selector Listed
Listed on the RIBA Product Selector — the primary specification tool used by architects across the UK.
Buy Poseidon — Available in Three Sizes
Poseidon 7kg
Small bathrooms, shower enclosures. Covers ~10–14m² at 1mm. Ideal for domestic bathrooms.
Buy 7kg →Poseidon 10kg ★ Most Popular
Standard bathroom / full wet room. Covers ~15–20m² at 1mm.
£100.00 excl. VAT
Buy 10kg →Poseidon 12kg
Large wet rooms, hotel bathrooms, commercial wet areas. Covers ~18–24m² at 1mm.
Buy 12kg →Also recommended: Copagro Sealant for sealing joints and pipe penetrations | Supergrip Primer for plaster, gypsum board and Hardie board substrates.
Ready to Waterproof Your Bathroom or Wet Room?
Available online with UK delivery. For project quantities, specification support or technical advice, contact our team.
Buy Poseidon Now Technical Enquiry →Frequently Asked Questions — Bathroom & Wet Room Waterproofing
Yes. UK building standards and the tile industry code of practice (BS 5385) require a waterproof membrane behind tiling in wet areas — particularly shower enclosures, wet rooms and areas within 500mm of water sources. Applying Poseidon before tiling creates a seamless vapour barrier that prevents water penetrating the substrate and causing damp, mould and structural damage.
A liquid waterproof membrane is a polymer-based coating applied to bathroom or wet room walls and floors before tiling. Unlike sheet membranes or tanking slurry, a liquid-applied product like Poseidon is brush, roller or spray applied and cures to a seamless, flexible, continuous film — with no laps, joints or fixings to fail.
No — this is one of Poseidon's key advantages. The elastic polymer formulation accommodates building movement and substrate variation without cracking, so no fabric corner tape or reinforcement is needed. This significantly reduces preparation time compared to traditional tanking slurry systems.
Yes. Poseidon bonds directly over existing tile floors and walls, making it ideal for bathroom refurbishments where stripping back to the substrate is not desired. Ensure tiles are clean, sound and properly keyed before application.
Coverage is approximately 15–20m² per 10kg at 1mm thickness. For a standard bathroom (walls + floor of a shower), 7kg or 10kg is typically sufficient. For a full wet room with floor-to-ceiling tiling, 10kg or 12kg is recommended. Contact us for advice on larger commercial projects.
Yes. Poseidon can be applied using an airless spray machine as well as roller or brush. Spray application is particularly useful for large commercial wet rooms, hotel bathrooms and leisure facilities where speed of application is important.
Poseidon holds a European Technical Assessment (ETA) and an Environmental Product Declaration (EPD) — making it one of the few bathroom waterproofing membrane products in the UK to hold both. The EPD provides independently verified environmental impact data for BREEAM assessments and net-zero construction specifications. It is also listed on the NBS Product Selector and RIBA Product Selector.
Yes. Poseidon is formulated for continuous contact with moisture and steam, making it suitable for steam rooms, spa facilities and saunas as well as standard bathrooms, shower enclosures and wet rooms.
Related Products & Pages
- Copagro Sealant — for use with Poseidon at joints and penetrations
- Supergrip Primer — required for plaster, gypsum and Hardie board substrates
- The GOAT — external waterproofing for flat roofs, terraces and balconies
- Waterproof Blue Liquid DPM — for floors, DPM and basement waterproofing
- Waterproofing for Schools & Education Buildings
- Architect & Specifier Hub — NBS Clauses, ETA & EPD Documentation
- Speak to Our Technical Team