STRUCTURAL ELEMENTS Get it right on the tiles

If you are looking to specify a tiled floor, it is crucial to understand what preparation is required to ensure that new or existing floor substrates are suitable. Stuart Ross of BAL looks at the different likely substrates, and the steps that need to be taken before tiling

loating floors are typically those not attached to a rigid substrate, so for example a tongue and groove or chipboard floor on top of a layer of insulation or acoustic material. Where this is the case, excessive movement in the subfloor is common and tiling directly to this type of subfloor without additional measures will likely result in the floor failing. As stated in BS 5385: Part 3, clause Floating floor: “Note 2: Direct fixing of ceramic tiles to a wood floating floor entails a high element of risk and where practicable should be avoided.” This is because the wooden floor is not supported in the same way as it would be by joists. So, support for the floor is limited.


Some floating floors often include heating pipes as well, which presents further challenges for rigid floor finishes especially where boarded systems are concerned. It is worth noting here however that floating timber boarded systems for rigid tile and stone finishes should be avoided in areas where water-fed heating pipes are installed, as this can cause excessive movement leading to tile failures. However, where the floor is deemed to be suitable to be tiled, one potential solution is to improve rigidity on non-heated floating floors by over-boarding the floor with 10-12 mm tile backer board or an additional 15 mm WBP grade plywood – sealed with an acrylic primer or SBR sealer. Boards should be installed staggered, so they do not coincide with any joints in the existing timber layer and leave a slight gap between the boards to allow for expansion. Use a tile adhesive as a bed below the board and screw the board at 300 mm centres, in accordance with British Standards. It is important that installers do not use nails, as movement in the floor can cause them to work free and cause problems down the line. Even if deflection is taken out of the floor sufficiently, we would recommend tiling with a flexible and highly deformable

S2 tile adhesive, as these have extra polymers to cope with any movement. Please note that even if you overlay the floor, it may still be possible that there is too much deflection in the floor, in which case the floor is unsuitable for receiving ceramic tiles. We would recommend contacting your adhesive manufacturer, who can provide onsite support to assist as well as further installation guidance.

Timber floors As with floating floors, timber floors should be structurally stable for tiling and be capable of carrying both static and dynamic loads without excessive deflection. This may mean the need to fit additional noggings between joists and replace any damaged or broken planks. We would recommend overboarding the timber with either a 12 mm tile backer board or a minimum 15 mm thick plywood of suitable quality, glued and screwed at 300 mm centres ensuring screw heads are flush with the surface.

If the floor needs to be levelled, then consideration should be given to using a suitable fibre reinforced levelling and smoothing compound. You must first prime the surface of the timber with two coats of neat acrylic primer, allowing it to dry between each coat and best practice to


Where a floating floor is on top of a layer of insulation or acoustic material, excessive movement in the subfloor is common, and tiling directly to this type of subfloor without additional measures will likely result in the floor failing


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