TN 23.24 Tiling to Timber Floors

INTRODUCTION
Before laying tiles on any timber base there are several factors which have to be taken into consideration, and these design considerations are detailed in the current British Standard Code of Practice BS 5385: Part 3: 2024. The appropriate mechanical properties required for floor finishes are discussed in this document.

There are several timber boards on the market, which are not suitable to receive ceramic tiling. Always check the suitability of the board to receive a rigid ceramic tile finish.

The design of the floor should take into account the initial drying shrinkage of the timber and subsequent movements due to seasonal moisture changes in mind the type of heating.

Timber floors of faulty construction have often behaved unsatisfactorily for a period of years as a result of surface evaporation of moisture.

The laying of floor tiles on a timber floor may also provide a more impervious covering, and in these circumstances the moisture content of timber may rise sufficiently to create conditions suitable for fungal attack (e.g. dry rot) to occur.

Before fixing commences it should be established that the ventilation is adequate and that effective damp proof courses are correctly located.

New Timber Floors
New timber bases should be designed not merely to carry the additional dead load (weight of the tiling system) but also the anticipated static/dynamic loading in service i.e. in order provide a stiff floor. Noggins may be required to fix between joists to ensure rigidity.

In particular:-
1. An appropriate sheet or board of a minimum of 15mm is recommended in BS 5385: Part 3: 2024.
2. The boards should be conditioned to adjust to the site conditions i.e. a moisture content appropriate for the site conditions
3. The lower face and edges are sealed e.g. with BAL BOND SBR to prevent moisture atmospheric moisture ingress and thus reduce risk of distortion/warping.

BS 5385: Part 3: 2024 recommends “Where it is necessary to further reduce or eliminate the risk of movement…or a proprietary tile backer board resistant to moisture and thermal movement should be screwed/bonded over the plywood at 300mm centres so that the joints in both layers do not coincide”

Existing Timber Floors
BS 5385: Part 3: 2024 recommends “Existing timber bases to be covered by tiles should be checked to ensure that they are sufficiently strong and rigid. They should be examined to determine whether they can carry the additional dead load of up to 0.8kN/m², and the probable dynamic loading, without excessive deflection. Existing boards should be removed and the floor stiffened with noggings and joist support sleeper walls before following the recommendations for new timber bases”

PREPARATION

NOTE: As of May 2024, Plywood/Timber is no longer a suitable base for floor tiling directly to BS 5385 -3: 2024
Option 1 - Overlay with a suitable tile backer board of appropriate thickness and fixed as per manufacturers instructions.
Option 2 - An uncoupling matting such as BAL FLEXBONE VARIED/2 EASY, BAL RAPID-MAT - can be selected providing that the plywood/timber floor is:
• the correct grade
• sufficiently dry, rigid and stable.
• able to carry all anticipated static and dynamic loads without deflection
• have adequate ventilation below.
• flat and level (SR1)
• securely fixed (screwed to joists at 300mm centres, including
any cross-noggins, if necessary).
When bonding tile backer boards or uncoupling mattings down to the surface of the timber, it should be prepared to receive a suitable BAL cement-based adhesive. Sanding of the surface may be required to ensure any surface coatings are removed, e.g. varnish, lacquers, etc. Prime with 2 coats of (second coat applied at 90⁰ to the first): BAL PRIME APD (undiluted). BAL ALL IN ONE PLUS (diluted 1:2 by volume with clean water) Allow each coat of primer to dry.

ADHESIVE
BAL FLEX ONE, BAL RAPID FLEX ONE adhesive or similar can be used. Tiles may be laid in a 3-6mm solid bed of adhesive, ensuring no voids are left beneath the tiles. The use of an uncoupling mat (e.g. BAL RAPID MAT) should also be considered.

GROUTING
Once the adhesive selected has set and dried thoroughly, joints, minimum 3mm wide, between the tiles may be filled using BAL GROUT FLEX WIDE JOINT or BAL MICROMAX3 ECO
Check for any potential risk of staining of tiles. Consideration should be given to the use of BAL PROTECTIVE SEALER prior to grouting especially with porous type tiles.
MOVEMENT JOINTS
Movement joints will be required in these installations. These joints should be a minimum of 6mm in width and to the full depth of tile and adhesive bed, and joints may be filled around perimeters and in light traffic areas using BAL MICROMAX SEALANT.

Movement joints should be incorporated as outlined in British Standard BS 5385-3. Briefly, this document requires that joints be located: -
a) Over existing and/or structural movement joints.
b) Around the perimeter of the floor and where tiling abuts columns, curbs, steps and plant fixed to the base.
c) In large floor areas tiles should be divided into bays of size not greater than 10m x 10m intervals.
d) On suspended floors the bay size should be reduced and additional joints provided over supporting walls or beams.
e) For floors subjected to significant thermal changes tiles should be divided into bays of size not greater than 40m² with an edge length not greater than 8m.

Note: Rubber-based materials may cause staining of silicone sealant. It will therefore be necessary to insert a bond breaker, e.g. PTFE tape to isolate the two products.

In shower areas/wet rooms the floor should be tanked. This is to ensure no passage of water to the underlying substrates. This may be achieved using BAL WATERPROOF 1C or BAL TANK IT.

TECHNICAL ADVISORY SERVICE
For free expert guidance on the use of BAL products, or any aspect of ceramic tiling with BAL products, contact the BAL TECHNICAL ADVISORY SERVICE on 01782 591120.
THE BAL 25 YEAR GUARANTEE
BAL products are supplied with a 25 year product guarantee. For further details and/or copies please contact the Company’s marketing department.
NOTE
The customer must verify the suitability of any information, opinion, recommendation or advice (“information”) provided by the Company for the particular application for which any goods are intended to be used and the Company accepts no liability (whether in contract, tort or otherwise) whatsoever for any loss, damage or expense arising from the misuse of any information it supplies, nor for the use of any information in or for applications which are unsuitable or inappropriate. Building Adhesives Ltd operates a continuous research and development programme and reserves the right to alter or to update information from time to time.

“Note: Any advice, opinion or information is given to assist the use of the Company’s products on the basis that the user will ensure its suitability for the application intended. In particular the Company cannot accept liability for loss or damage which may arise from incorrect use of its products or from poor workmanship. The Company operates a continuous research and development programme and reserves the right to update information without notice.”