Stone and timber in wet areas

At a glance

What the sources read say, not a verdict. 'No source read' means we found nothing usable, not that the surface is unsuitable. Partner workshops confirm suitability for each stone and timber.

Four kinds of wet

Wet areas are not one condition. A dry dressing room, a bathroom floor that gets splashed, a shower or steam room that is wet every day, and a pool surround that is wetted for hours each ask different things of a surface, and the sources we could read describe them differently. The drawing separates four kinds. They are working terms for this sheet, not terms from a standard.

Three points frame the rest. First, floors in a workplace must have effective means of drainage where necessary (Workplace Regulations 1992, regulation 12(2)(b)). Second, Approved Document M volume 2 asks for the floor of an accessible shower and shower area to be slip resistant and self-draining (5.18 o), and the floor of an accessible bathroom to be slip resistant when dry or when wet (5.21 c). Third, the electrical ‘zones’ of a bathroom, which govern luminaires, are a different idea from the wetness of a floor: see bathroom zones and luminaires.

What the sources say about each surface

What the evidence is. The matrix is what we could read, not a verdict. The most specific UK guidance, the Stone Federation’s code of practice for natural stone in bathrooms, shower enclosures and wet rooms, is free to members and by request to others, and we did not read it. Most of what is said about stone below comes from one supplier’s technical manual for one limestone, from the Natural Stone Institute through our types of natural stone sheet, and from the Stone Federation’s consumer pages. The Stone Federation’s own advice for bathrooms is to give particular attention to slip resistance and to make sure the stone is technically suitable for repeated wetting and drying. Your stone partner confirms suitability stone by stone.

Stone. The one limestone supplier read says its honed Portland stone has been used in bath and shower surrounds and steam rooms (with specialist advice on sealing and maintenance), and in pool surrounds, but does not recommend it for pool internal linings, public toilet floors, kitchen worktops, vanity units or shower trays. That is one stone’s position, not a rule for limestone. On finish, a Singapore government guide to stone finishes says most natural stones grip well when clean and dry whatever the finish, and that grip may fall when wet or contaminated, especially if polished; it does not give values. Natural stone finishes compares the finishes.

Timber. Two flooring makers read give a consistent warning and one useful detail. A maker of engineered wood floors says they suit most rooms but are not recommended for wet rooms, which it defines as the bathroom, toilet and laundry. A parquet maker says it does not recommend timber floors in wet rooms, and, for a damp bathroom, recommends a two- or three-layer construction in a species that moves little (oak is its example), a room held at 20 °C and 60 per cent relative humidity, a row or two of tile or stone next to the bath, shower or basin, ventilation each time the bath or shower is used, and renewing the oil when water stops pooling on it. Neither is a standard, and a product’s own warranty and installation guide decide. For slatted hardwood such as teak we found no usable source: ask for the species’ durability class and the use class the product is intended for, which BS EN 350 and BS EN 335 define.

Common mistake. Choosing a surface by how it looks wet. A polished stone on a shower floor, or timber run into a shower threshold, can look right in a render and still be the wrong choice. Decide the zone, the finish, the test and the threshold before the surface.

Waterproofing, falls and the build-up

The drawing shows a wet-room floor in section, from the wall to the dry timber floor beyond the door. It is a principle drawing, not a detail: the waterproofing system maker and the installer set the dimensions.

• Tanking. The Tile Association, summarising BS 5385-1:2018 clause 6.1.1.3, says that in wet areas such as showers, wet rooms and steam rooms the substrate should be protected with a suitable proprietary tanking membrane system, which can be a sheet membrane or a liquid-applied water impermeable product. It also says that water-resistant adhesive and grout are no substitute for a tanking system, as BS 5385-4 states. Those are tile standards: BS 5385-4:2015 is titled for ceramic and mosaic tiling in specific conditions such as wet areas, and BS 5385-3:2024 covers stone floors in normal conditions. Which document governs natural stone in a wet area is for the stone installer to say, and the Stone Federation’s code is the document written for it.
• Falls and drainage. Water has to reach the drain. Regulation 12 and Approved Document M say so in general terms. We give no fall: trade pages we saw disagreed and we read no document that sets one. Take the fall from the system maker’s data sheet and the installer, and draw it.
• Curing before use. The Tile Association says a newly tiled shower should wait a minimum of 14 days before it is used, as it reports BS 5385-4 recommends. Ask the system maker whether the same applies to stone and its adhesives.
• Movement. Stone, screed and timber move differently. Joints are carried through the full depth of the build-up, and where the waterproof layer crosses a joint it needs detailing by the system maker. See floor transitions and movement joints. For a heated floor see underfloor heating under wood and stone: the bathroom surface temperature limits found in the sources there disagree.
• Where wet meets dry. The threshold is where most wet-room trouble starts. Fall the wet floor away from the timber, keep the timber on its own substrate with a gap, and seal the joint.

Slip in wet areas

Wet areas are barefoot areas. HSE says Slider 55 is the pendulum rubber for barefoot areas, and that the pendulum is its preferred test in dry and contaminated conditions. HSE’s three PTV bands and the standard that replaced BS 7976 are on the slip resistance sheet, which gives no target for any room and neither does this one.

• Test the finished surface, wet. HSE notes that a floor’s slip resistance can change with installation, grouting, cleaning or polishing, and the Stone Federation’s 2011 guide asks buyers to check that the slip values relate to the surface finish being considered.
• Do not rely on a ratings label. HSE’s FAQ says a floor described as R9 will be slippery when wet, and that if a maker does not claim a floor is slip resistant when wet it probably is not.
• Do not add grip afterwards without advice. HSE’s FAQ says acid-etch treatments change appearance and may use hydrofluoric acid, which carries serious health risks. See the slip sheet.

Steam, hard water, chlorine and cleaning

Steam, hard water, soap and cleaners all work on a surface, and the sources we could read say little about them for stone. The limestone supplier’s manual says bleach, household soaps and detergents should be avoided, that acidic products such as cola and red wine can attack and stain limestone, and that spills should be wiped up promptly with clean water. It suggests an impregnator for water repellence in some applications and says to check the impregnator suits the stone. The Stone Federation advises regular cleaning with a pH-neutral cleaner. Some bathroom cleaners and descalers are acidic, so ask the stone partner and the sealer maker which products are safe for the stone you have chosen, and write them into the care instructions.

For pool halls, chlorine and salt are further questions on which we found no usable source. HSE’s guide to health and safety in swimming pools (fourth edition, last updated February 2024) says it no longer contains detailed pool design information, and the pool water treatment body’s guidance and Sport England’s design guidance were not read. Put those questions to the pool designer and the stone partner before a surface is fixed.

Floor and wall surface to [shower / wet room / steam room / pool surround]: [stone and quarry reference / timber species and system], [finish], format [ ] mm, to match approved sample [ref] taken from the production slab. Suitability for the [zone] is to be confirmed in writing by [stone workshop / joinery partner] before order, with its sealing and maintenance regime.

Falls of [ ] to [drain type and position], formed in the substrate before waterproofing. Waterproofing: [proprietary tanking system, sheet or liquid applied], installed to the system maker's instructions by an installer approved by the system maker, continuous over the floor and [height per system maker] up the walls, and sealed to the drain. Testing and curing before use: [as the system maker instructs and BS 5385-4, not less than [ ] days].

Wet pendulum test per [slip resistance clause] with Slider [55] for barefoot areas, on a production sample finished and sealed as the works will be. Target PTV [ ] set by [designer / duty holder].

Movement joints carried through the full depth of the build-up as drawing [ref], sealed with [flexible sealant] and detailed with the waterproofing system maker where the waterproof layer crosses them. Threshold between wet floor and dry timber floor as detail [ref]: wet floor falling away from the timber, timber on its own substrate with a gap of [ ] mm sealed with [ ].

Cleaning and maintenance products to be those approved in writing by [stone workshop or joinery partner] and [sealer or oil maker]. No bleach, household soap, detergent or acid descaler unless so approved. Sealer or oil renewal interval [as the maker states].

Standards and sources

• Stone Federation Great Britain: Natural Stone, Installation in Bathrooms, Shower Enclosures and Wet Rooms: publication page read 5 Nov 2026; the code (free to members) was not read.
• The Tile Association: FAQs and a presentation on BS 5385-1:2018: tanking and the 14-day wait, as reported there; read 5 Nov 2026. The BS 5385 parts were not read; BSI listings of BS 5385-3:2024 and -4:2015 only.
• HSE: Assessing the slip resistance of flooring (GEIS2) and slips FAQ: Slider 55 for barefoot areas, R9, acid etching; read 5 Nov 2026.
• Workplace Regulations 1992, reg 12(2)(b); Approved Document M volume 2, paras 5.18 (o) and 5.21 (c): drainage; slip resistant and self-draining shower floors. Editions as on the slip sheet; read 5 Nov 2026.
• BS EN 335:2013 and BS EN 350:2016: use classes; natural durability. BSI listings only; not read.

Questions we are asked

Can marble be used on a shower floor?

Published views differ. The Natural Stone Institute says many marbles suit tub decks and showers, while a Singapore government guide says polished stone's grip can fall most when wet, and one limestone supplier does not recommend its stone for shower trays. It depends on the stone, the finish, the falls and waterproofing, and a wet barefoot test. Ask the stone partner, and test the finished surface.

Can I put a timber floor in a bathroom?

Two flooring makers advise against timber in wet rooms. One describes the conditions for a damp bathroom: a two- or three-layer oak floor, 20 degrees and 60 per cent humidity, tile or stone beside the bath and shower, ventilation, and renewing the oil. The product's warranty and installation guide decide.

What waterproofing does a stone wet room need?

The Tile Association, summarising BS 5385-1:2018, says showers, wet rooms and steam rooms should have a proprietary tanking membrane system, and that water-resistant adhesive and grout are no substitute. Those are tile standards. The Stone Federation has a code for stone in wet rooms, which we did not read. Ask the installer which system and which document they follow.

What fall should a wet-room floor have?

We give no figure: the trade pages we saw disagreed and we read no document that sets one. The waterproofing system maker's data sheet and the installer set it. Approved Document M asks for accessible shower floors to be self-draining.

How long before a newly tiled shower can be used?

The Tile Association says a minimum of 14 days, as it reports BS 5385-4 recommends. That is for tiling; ask the system maker and the stone installer whether stone and its adhesives differ.

Can the same stone run from the bedroom into the shower?

As a design choice, yes, but the build-up under it changes: the wet zone needs falls and tanking, the boundary needs a threshold or movement joint, and the slip requirement differs. See the floor transitions sheet.