DUO BOARD – HDF Free Floating Sub-floor
The DUO BOARD is an HDF (high-density fiberboard) free-floating sub-floor system designed as a floor preparation system and vapour barrier. It is suitable for the immediate glue-down of all resilient floorings, including sheet vinyl, LVT, linoleum, cork, rubber, carpet, and carpet tiles. For optimal performance, it should be used in conjunction with the Wunda 800g/200mu vapour barrier.
Installation of the DUO BOARD system should only commence after ensuring all heating boards are securely bonded, floor heating pipes are fully seated in their channels, and a complete pressure test of the floor heating system has been successfully carried out.
DUO BOARD offers a quick, simple, and dry installation method. It features very low thermal resistance, allowing heat to transfer efficiently for a rapid response and maximum comfort from underfloor heating systems. The installation is designed to be easily removable without damaging the original floor finish, if required.
Made from highly compressed engineered wood fibers, HDF is denser and stronger than medium-density fiberboard. DUO BOARD is specifically engineered as a free-floating sub-floor for installation over floor heating, providing a smooth, stable, and level base.
It is crucial to protect the DUO BOARD system by installing the Wunda 800g/200mu vapour barrier between the Rapid Response boards and the heating pipes before laying the DUO BOARD. The vapour barrier should be laid across the entire surface of the floor heating boards and pipes.
The DUO BOARD system comprises two layers: a 4mm base board with an adhesive surface and a 3mm top board. Boards are laid in an overlap or brick bond fashion. The 4mm base board is laid first with its adhesive side facing up. The 3mm top board is then laid in a brick bond pattern onto the exposed adhesive surface, creating a seamless finish that prevents 'joint lines' from showing through the final floor covering. Once laid, joints can be sanded to achieve a smooth floor deck for bonding.
Expansion gaps are essential, recommended at a ratio of 1mm per linear metre. For example, an 8-metre length requires an 8mm expansion gap around all edges.
DUO BOARD is not suitable for use in bathrooms, wet rooms, en-suites, or any other areas prone to moisture, as the boards will expand upon contact with water. DUO BOARD is not a structural sub-floor and cannot be used as a replacement for floor boards or decks.
Installing DUO BOARD
DUO BOARDS are installed in two layers, following specific cutting instructions. The first base layer requires boards with the adhesive facing up; do not remove the adhesive protective cover at this stage. Lay boards one room or area at a time.
Do not use the adhesive facing to bond the boards sticky side down to the surface below.
Once the area is covered with the base layer of boards arranged in a brick bond fashion with the adhesive side facing up, the top layer of boards can be laid in a brick bond fashion, staggering the joints to overlap the joints in the base boards. Ensure boards are laid tightly together with no gaps. Correctly laid DUO BOARDS provide a seamless sub-floor, preventing visible joints in the final floor finish. DUO BOARDS are a free-floating sub-floor designed for installation over all types of floor heating systems. Suitable carpets (max 2 tog), vinyl, or linoleum can be glued using a suitable adhesive directly onto the DUO BOARDS system or simply laid freely on top.
Before purchasing or installing your chosen final floor finish, always check with your supplier for compatibility with DUO BOARD and your floor heating system.
Base Layer Installation
Lay DUO BOARDS in a brick bond fashion, staggering the joints, while leaving an 8-10mm expansion gap around outside walls, pipes, and fixed objects.
- Before commencing, ensure the area is clean, dry, level, and free from dust, debris, or any objects that could prevent the DUO BOARDS from lying flat. Lay the Wunda vapour barrier onto the base floor, ensuring it is flattened without creases. Allow the barrier to extend up the walls by approximately 50mm. Overlap the vapour barrier by 200mm along all seams and tape the joints. Any excess can be trimmed off once the final floor has been installed.
- The first row of base boards will require cutting the boards in half along their length, with the cut edges placed against the wall. The first board laid in this row must be 3/4 of its length. Again, place both cut edges facing the wall. Leave an 8-10mm expansion gap between the DUO BOARDS and outside walls, pipes, and fixed objects. Lay out the remaining base boards end to end in the first row with the adhesive side facing up; do not remove the adhesive protective film yet.
- The second row of base boards can now be laid in the same direction as the first row. The first board in the second row must be cut to 1/4 of its length, again with the cut side facing the wall and the adhesive side facing up, leaving the protective film on the boards. Place a full-length board end to end with the 1/4 cut board; the leftover offcut will be used to start the third row. Ensure base boards are laid tightly against each other, leaving no gaps between the boards.
- Repeat cutting steps 1-3 for the rest of the rows, staggering the boards in a brick bond fashion.
- Do not remove the adhesive protective film and keep your workspace clean and free from dust.
Top Layer Installation
Once all base boards have been cut and laid with the adhesive protective film still attached and facing up, the top layer of DUO BOARDS can be systematically laid on top.
- Lay the top layer of DUO BOARDS in the same direction as the base boards, maintaining an 8-10mm expansion gap around outside walls, pipes, or fixed objects. Ensure the base boards are laid flat; investigate and remedy any 'high' spots or areas where the boards are not laid flush. Vacuum the area to remove any debris and dust before removing any adhesive protective film or fitting the top layer.
- Returning to the first row where the cut base boards were laid, remove enough adhesive protective film to expose an area you can comfortably work with, ideally not much bigger than a full-size board at a time.
- Remove the adhesive protective film from the base boards. Select a full-size top DUO BOARD and carefully position it onto the exposed adhesive. Check for alignment while also checking the base boards for movement and gaps. Gently lower the top board onto the exposed adhesive, smoothing across the board as you lay it. The top board can be gently tapped with a rubber mallet to ensure adhesion, taking care not to damage the boards.
- Keep the joints between the top layer of boards as tight as possible, laying the boards end to end in a brick bond fashion. Start the second row with a 1/2 length board. Lay the second row in a staggered brick bond fashion, ensuring the joints in the base layer are covered.
- Systematically lay each row of top layer DUO BOARDS one row at a time, removing the adhesive protective film as you go. Keep the lines straight and each board tight up to the last one laid. Lay each room or area separately, ensuring an expansion gap of 8-10mm around all walls, pipes, or fixed objects.
- If your final floor finish is to be glued onto the DUO BOARDS surface, check with your floor finish supplier for suitable adhesives, compatibility, and installation instructions.
Special Considerations for Temperature Sensitive Floors
Temperature-sensitive floor finishes, such as LVT and wood flooring, require temperature-limiting probes to be installed before the final floor finish is laid. A maximum floor surface temperature of 27°C is required. Wunda can supply floor probes at the point of estimate. DUO BOARD will need routing to allow flush fitting of floor probes so that the probe is in contact with the underside of the temperature-sensitive floor finish.
Illustration showing the protective film peeled back on a baseboard, revealing the adhesive surface.
Diagram indicating an 8-10mm expansion gap around outside walls.
Diagram illustrating boards laid in a staggered brick style pattern.
Technical Specifications
Duo Board
| Technical Information | Details |
|---|---|
| Board size (each) | 1200 x 600mm |
| Top board thickness | 4mm |
| Base board thickness | 3mm |
| Composition | HDF fitted with interactive adhesive on base board |
| Density kg/cm² | 770 |
| Bending strength kg/cm² | >40 |
| Humidity (%) | 4-10 |
| Thermal Rm value (m².K.W.-1) | 0.047 |
| Fire classification DIN 4102 | B2 |
| Storage | In a dry place, horizontal position |
Vapour Barrier
| Technical Information | Details |
|---|---|
| Description | Natural Mono CFS Reel |
| Substrate | LD Virgin (Medium - High Slip) |
| Density | GP low density (LDPE) |
| Colour | Natural |
| Size of product | 1200/2400MM |
| Thickness | 200μ |
| Air perforations | None |
| PIFA tolerances | Size: ± 3% Thickness: ± 10% Quantity: ± 10% Please note that with very short runs or very small bags/sheets, the tolerances increase. |
| Other Info: | *30% RECYCLED CONTENT* |
| Full product description: | 1200/2400MM (47 1/4 94 1/2) 200μ (800g) Natural LD Virgin Shrink (Medium - High Slip), CFS Reel - EXTRAS: *30% RECYCLED CONTENT* |
| LDPE TEMPERATURE PARAMETERS | SOFTENING POINT - 90°C to 120°C MELTING POINT - 130°C to 150°C |
Resources and Important Notes
Resources
Visit our How-To Videos page to watch the Wunda Duo Board and Vapour Barrier installation guide: ? wundagroup.com/support/how-to-videos/
Important Notes
When laying DUO BOARD, allow an expansion joint every linear 8 metres. The expansion joint should be between 5mm to 10mm and can be filled level with the board surface using a flexible sealant/filler.
You cannot use tile adhesive or levelling compounds on these DUO BOARDS.
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