Interior and finishes · Tiles & Stone
Wet Room Floor Former (Pre-Sloped Shower Deck)
Where a pre-sloped former sits within a wet room floor build-up, how it differs from a flat backer board, and why it is not itself the waterproofing layer.
Educational reference entry. Suitability depends on the complete assembly, substrate, exposure, installation method, manufacturer documentation, local requirements and qualified professional review.
Overview
What wet room former is
A wet room floor former is a rigid panel manufactured with the fall already in it. Most are an extruded polystyrene or similar core faced with a reinforced cement or polymer coating, though timber-based and fibre-cement versions exist. The upper surface slopes towards an aperture that receives a centre outlet or a linear channel, and formats are made both for timber joisted floors, where the panel is recessed into or laid over the joists, and for solid floors.
The closest thing it is confused with is a tile backer board, and the two are opposites in one respect. A backer board is manufactured flat, and its purpose is a stable plane substrate for tiling. The former's purpose is that it is not flat: the fall is built into the product, and the drain position and body are part of the panel's geometry rather than something added underneath it afterwards. Trying to create the fall by building it up in adhesive or levelling compound under a flat board is the usual reason a finished floor drains towards the wrong place.
What the former is not is the waterproofing. It is one component in a wet room floor assembly, and the watertight layer is a separate designed system, bonded across the former and detailed at the outlet, at the wall junctions and at every penetration. Whether the finished construction keeps water where it belongs is determined by that system, by the standard of the detailing and by a qualified professional's design, not by the presence of a former. Structural questions, including trimming joists and forming the recess, sit in the same category.
Terminology
Common names and aliases
These names describe the same thing. The library keeps one entry per material so that an acronym, a trade name or a regional spelling never becomes a second, thinner page.
- shower tray former
- wet room deck former
- pre sloped shower base
Applications
Common applications
Where this material is typically encountered. A typical application is not a statement that it suits your project.
- Level-access shower areas in a wet room where no upstand or tray edge is wanted.
- Shower areas over timber joisted floors, where the panel is recessed within the floor construction.
- Shower areas on solid floors, where the panel raises the deck and forms the fall above the slab.
- Accessible bathrooms where the shower floor has to be continuous with the surrounding floor.
- Refurbishments where a tiled level-access area is replacing a moulded tray.
- Areas served by a linear channel drain positioned at a wall or at the entrance to the shower zone.
Consideration
Where it is commonly considered
- Where a level-access shower area is required and the fall has to be built inside the floor construction.
- Where a tiled shower floor is wanted rather than a moulded tray, and the design has been reviewed by a qualified professional.
- Where the drain type and position have been established early enough to select a matching panel.
- Where the floor construction can accommodate the recess, and that has been assessed structurally.
- Where the manufacturer's waterproofing system and the former are being taken from the same source and specified together.
Professional review
Where additional professional review is especially important
These are the situations where the answer depends on the specific building, and where a qualified professional should be involved before anything is decided.
- Where the drainage route below the floor has not been designed, since the outlet position governs everything above.
- In a timber floor where the structural implications of recessing or trimming have not been assessed by a qualified professional.
- Where the former is being relied on as the waterproofing layer, which it is not.
- Where the finished floor level, threshold and door swing have not been coordinated with the build-up depth.
- Where the tile format chosen cannot follow the fall without lipping at the drain.
Properties
Key properties to discuss
Qualitative topics worth raising. Measured values, classes and grades come from the manufacturer's technical documentation for the specific product, not from a reference page.
- Substrate dependency
- The former sits on the floor construction and hands its loads to it, so the deck beneath has to be sound, adequately supported and prepared as the manufacturer requires. The structural work is assessed by a qualified professional before any panel arrives.
- Installation dependency
- The panel is bedded and fixed as the maker instructs, with the outlet body positioned first and the drainage connected below. The sequence runs from drainage upwards, and it is very difficult to correct anything once the waterproofing is on.
- Moisture behaviour
- The former establishes where water goes; it does not stop water going anywhere. A separate waterproofing system provides that, bonded to the former and detailed at the outlet, the walls and every penetration by whoever designs it.
- Thermal behaviour
- Where underfloor heating is present in the same construction, compatibility with the panel and with the waterproofing has to be confirmed from the documentation of every product involved rather than assumed from the build-up.
- Repairability
- Everything about this component is buried under a waterproofing layer and a tiled finish. A later fault means removing the tiling and the waterproofing to reach it, so the detailing done once is the detailing that has to last.
- Documentation
- Ask for the maker's installation instructions, its compatibility statement covering the waterproofing system and the drain, and its guidance on the tile formats the graded surface will accept.
Exposure
Exposure and environmental conditions
- How heavily will this shower be used, and by how many people each day?
- Is the area fully open to the room, or is it contained by a screen or a partial enclosure?
- Where is the extract ventilation, and how quickly will the area dry between uses?
- Is there underfloor heating in this construction, and has every product maker addressed that?
- What is below this floor, and what would the consequences of a leak be there?
Assembly
Substrate and system dependencies
What this material sits on, is fixed to or depends on. This is usually where performance is won or lost.
- The drainage connection below the floor determines the outlet position and has to be resolved first.
- Joist trimming, support and deck construction are assessed and designed by a qualified professional.
- The waterproofing system, the former and the drain are chosen for compatibility with one another.
- Wall junctions and any upstand at the perimeter are detailed as part of the waterproofing, not the panel.
- Finished floor level, threshold heights and door clearances are coordinated with the total build-up.
- The tile chosen has to be able to follow the graded surface, which limits how large a format works.
Appearance
Appearance and finish considerations
- The fall is visible in the tiled surface, and larger tiles show it as facets rather than as a smooth plane.
- Drain position and orientation are strong visual elements in a small tiled floor.
- A linear channel at a wall reads very differently from a centre outlet with tiles falling in from four directions.
- Tile joint layout is set out from the drain, since that is where any error becomes obvious.
- The junction between the shower area and the surrounding floor is a designed line whether or not there is a threshold.
Durability
Durability questions
Questions to raise rather than a service life to expect. No material has a universal lifespan — it depends on the assembly, the exposure and the upkeep.
- What loads will this deck carry, including seating, grab rails and anyone leaning on them?
- How has the panel been supported at its edges and around the drain aperture?
- What would the first visible sign of a problem be, and where would it appear?
- How is the drain going to be accessed for cleaning over the life of the installation?
Upkeep
Maintenance and repair considerations
- How is the outlet or channel cleared of hair and debris, and can that be done without tools?
- What is the plan if a fault develops beneath the tiling, and who would investigate it?
- Is a record of the products used and the details followed being handed over to the owner?
- What routine cleaning does the tiled surface need, and does it affect the sealant joints?
Installation
Installation dependencies
What the installation depends on — not how to do it. Method belongs to the manufacturer's instructions and the trades carrying out the work.
- Drainage below the floor is completed and tested before the panel is fixed in place.
- The panel is bedded and fixed exactly as the maker instructs, since fixings through it are a risk.
- The waterproofing system is applied over the former as a separate operation with its own detailing.
- Tiling starts only once the waterproofing has been completed and checked in the manner its maker sets out.
- The tile format and layout are agreed against the fall before tiling begins.
Documentation
Documentation to request
Ask for these in writing, for the specific product being proposed, and keep them with the project record.
- The maker's installation instructions for the exact panel, drain and floor construction.
- A compatibility statement covering the former, the waterproofing system and the drain together.
- Guidance on the tile sizes and formats the graded surface will accept.
- Maintenance instructions for the outlet or channel and its removable components.
- Any structural information the maker provides about spans, support and loading on the panel.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- Who is designing the waterproofing for this floor, and which system is being used?
- Has the drainage route below the floor been resolved before the panel was selected?
- What structural work does recessing this panel involve, and who has assessed it?
- How will the waterproofing be detailed at the drain, at the walls and at every penetration?
- What tile format is proposed, and will it follow the fall without lipping?
- How does the finished floor level relate to the door, the threshold and the surrounding floor?
- What testing or checking will be done before the tiling covers the waterproofing?
- Who is responsible if a fault appears later, given that several products are involved?
Blind spots
Commonly overlooked points
- The former is mistaken for the waterproofing, which is the single most consequential misunderstanding in a wet room floor.
- Drainage below the floor is discovered to be in the wrong place after the panel has been ordered.
- Large-format tiles are chosen for the room and then have to be cut down to follow the fall.
- Nobody checks the total build-up against the door and threshold until the floor is already raised.
- Products from different makers are combined without any of them accepting the combination.
What this page does not do
- A floor former is a component within a wet room assembly. It is not a waterproofing layer, and its presence tells you nothing about whether the finished construction is watertight.
- No waterproofing, tanking or drainage specification is given here; all of it is designed by a qualified professional using the chosen system's documentation.
- No falls, levels or panel dimensions are stated, because those are set by the specific product and the design.
- Structural alterations to a floor to accommodate a recessed panel must be assessed by a qualified professional before work begins.
- This reference is published for education only, and its publisher does not test, approve or endorse formers, drains or waterproofing systems.
Related entries
Related materials
Materials from the same family, an adjacent role in the assembly, or a shared application.
Inspiration
Related Ideas Library pages
Design directions where this material commonly appears.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this material comes up.
Go deeper
Related Build Design Hub guides
Planning guidance and neutral comparisons behind the decisions on this page.
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