18mm Flat Dry Screed Overlay Board for UFH Non Routed

Description

The 18mm Flat Dry Screed Overlay Board is a non-routed, flat-surface overlay panel designed to sit directly over grooved underfloor heating insulation boards. It gives you a smooth, stable, tile-ready surface at just 18mm thick, without a wet screed pour or the added floor height that comes with one.

Each 1200mm x 600mm board covers 0.72 m² and has tongue and groove edges that interlock and are bonded with joint adhesive, so no screws are needed. Thermal performance is strong for such a slim build-up: a thermal conductivity of 0.40 W/mK and a very low thermal resistance of 0.045 m²K/W let heat pass quickly from the pipework into the floor finish, which suits low flow temperature systems such as heat pumps as well as boilers.

Specify this board when the pipe is already housed in grooved insulation and you only need the covering layer for tiling or a self-levelled finish. Supplied with a minimum order of 10 boards (7.2 m²).

18mm

Board thickness

1200 x 600mm

Board size

0.72 m²

Coverage per board

0.40 W/mK

Thermal conductivity

0.045 m²K/W

Thermal resistance

Tongue & groove

Screw-free edges

Designed to cover grooved insulation boards

This is a flat board with no grooves. It is made to be laid directly onto grooved insulation boards to create a durable, level surface for tiling.

Joint adhesive is required

Joint adhesive must be used on all joints and is sold separately. The manufacturer calls for a 2-3mm layer of adhesive along the board edges, allowed to dry fully before the next stage. Add it to your order.

Solid, stable base required

Lay on a solid, stable, dry subfloor. Timber floorboards must be screwed down firmly with no movement, and new screed or concrete must be checked for moisture before installation. Where a floor has to span joists, ask us about a structural load-bearing panel instead.

Key features

Flat, non-routed surface

A solid, groove-free face that gives a clean, continuous base over grooved insulation boards.

Low profile at 18mm

Only 18mm thick, keeping floor build-up to a minimum on retrofit and new-build projects alike.

Fast heat transfer

0.40 W/mK conductivity and 0.045 m²K/W resistance deliver rapid heat response and help the system run efficiently.

Screw-free joints

Tongue and groove interlocking edges are bonded with joint adhesive for quick, simple installation without screws.

Stable and tough

Low thermal expansion, high impact resistance, and it does not contract or expand like chipboard when exposed to water.

Tile ready

Accepts ceramic tiles directly, so you can go from board to finished floor without extra screed layers.

Technical specification

Product

Brand

ThermRite

Product type

Flat (non-routed) dry screed overlay board

Manufacturer code

GYPDECK 18

Edge profile

Tongue and groove, bonded with joint adhesive (no screws)

Dimensions and coverage

Board thickness

18mm

Board size

1200mm x 600mm

Coverage per board

0.72 m²

Minimum order

10 boards (7.2 m²)

Thermal performance

Thermal conductivity

0.40 W/mK

Thermal resistance

0.045 m²K/W

Thermal expansion

Low

Performance and finishes

Surface

Flat, no grooves

Impact resistance

High

Moisture behaviour

Does not contract or expand like chipboard when exposed to water

Floor finish

Accepts ceramic tiles directly

Joint adhesive

Required on all joints, sold separately

Frequently asked questions

Does this board have grooves for the heating pipe?

No. This is the flat, non-routed version. It is designed to be laid over grooved insulation boards that carry the pipework. If you want the pipe routed into the overlay board itself, choose a routed board from the same range.

Do I need joint adhesive, and are screws required?

You need joint adhesive on all joints, but no screws. The tongue and groove edges interlock and are bonded with adhesive, which is sold separately. The manufacturer calls for a 2-3mm layer along the board edges, allowed to dry fully before moving on to the next stage of the installation.

Can I tile directly onto the board?

Yes. The board is designed to accept ceramic tiles directly. Use a flexible adhesive suitable for underfloor heating and follow the tile and adhesive manufacturers' guidance. Check the heat-up and commissioning requirements for your tiles before laying.

How many boards do I need?

Divide the floor area in m² by 0.72 and round up, then allow for cuts and offcuts. For example, a 15 m² area needs 15 ÷ 0.72 = 20.8, so 21 boards before any wastage allowance. The minimum order is 10 boards (7.2 m²).

How should the boards be laid, and what subfloor preparation is needed?

The subfloor must be solid, stable, dry and clean, with loose material removed and floorboards screwed down firmly. Check moisture content on new screed or concrete. Leave a 10mm expansion gap at the room perimeter and lay boards in a brick pattern, starting alternate rows with a half board. Full details are in the manufacturer's installation guide.

Can I use other floor finishes, and is it suitable for heat pumps?

The board is intended for tiled finishes. For vinyl, bonded wood or carpet, the manufacturer's guidance is to self-level the surface first. Always confirm the maximum permitted floor temperature with your flooring supplier, as around 27°C is commonly cited for wood and laminate. The board's low thermal resistance helps heat reach the floor surface at lower flow temperatures, which is valuable with heat pumps.

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Room Dimensions

Length (in m):

Width (in m):

Height (in m):

Room Type

Living Room

Bedroom

Kitchen

Bathroom

Conservatory

Hallway

Glazing Type

Single Glazed

Double Glazed

Triple Glazed

External Walls

0 Wall

1 Wall

2 Walls

3 Walls

4 Walls

Insulation Level

Poor

Average

Good (New Build)

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Required Heating

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Watts

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