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External tiling – a great opportunity, if it’s done right

This month Jim Percival, technical director at Palace Chemicals, looks at the increasingly popular trend for tiling external areas, as well as the possible pitfalls and challenges involved.

It is now a well-established trend for homeowners to maximise the outside space available to them around their homes. Surveys have shown that the usability of exterior areas ranks alongside the size of rooms and the proximity of local services as key factors influencing purchase decisions on the UK housing market. This is a trend which is also reflected in the commercial market, as the hospitality sector seeks to make the most of any external space that is available to them.

Often external areas are tiled using 20mm porcelain tiles or natural stone, which enable design themes to be created which either complement or contrast with tiled surfaces installed internally in buildings. The continuation of internal design themes to the exterior of a building is an important trend, leading to a blending of internal and external space.

There are plenty of tiles and natural stone products on today’s market, which will do an excellent job in external locations. Problems however can arise at the installation stage. Often these jobs are done by builders or keen DIYers, rather than by experienced and knowledgeable 4 tile fixers or landscapers. This can lead to problems if correct procedures (especially with regard to preparation of the substrate) are not followed.

A landscaper will take a different approach to this issue, compared to a tiler. A landscaper will not normally want to create a concrete base for laying the tiles. He or she would begin by evaluating the designated area to determine its suitability – ensuring the ground is level and free of any loose debris, vegetation, or standing water that may interfere with the installation. If necessary, the area will be excavated to a depth of around 150–200mm to create a stable base and fully remove any existing materials such as grass, soil or old paving to enable a solid foundation for the tiles. On to this a compacted Type 1 (MOT) base can be laid.

Once the sub-base is prepared and fully compacted, the next stage is to lay a permeable
bedding mortar to a suitable depth. This will allow any water or moisture pass through the installation freely and drain away.

A tiler, on the other hand, would want to work on a concrete substrate and would use a flexible adhesive, bearing in mind the maximum bed depth of the individual adhesives, using a 20mm round notched trowel to fix the 20mm porcelain tiles.

Both types of installation would require the use of a priming slurry to ensure a good bond between the tiles and the appropriate adhesive. After drying, they would be grouted in the colour and type of grout of the customer’s choosing.

Exterior installations are likely to be affected by significant environmental changes, e.g. temperature variations, freeze thaw cycles and weathering, placing greater demands on the whole assembly. Therefore, the correct design of the floor build-up and the selection of the right materials is essential to maximise longevity and performance.

It is important to ensure that any water impacting on an external tiled surface, such as rain water or melting snow, is managed. Trapped moisture at lower levels within the floor construction can create voids over an extended period as water freezes and expands. The more voids present, the greater the risk of cement-based elements becoming unstable.

Adequate drainage should be installed with appropriate falls built into the design to achieve efficient removal of surface water. Falls should always be directed away from the building, and provision for appropriate sealing and waterproofing should be made at the junction between the tiled installation and the property. Poorly constructed assemblies can lead to significant problems with both visible surface damage – such as cracking and/or debonding tiles, efflorescence and joint erosion, patchy or stained tiles and potentially unseen damage to the substrate/base. These are all indicative of excessive water residing within the assembly for longer periods of time than intended or designed for.

In certain installations, there is also a requirement for a waterproof substrate below the tile to avoid water that penetrates below the tile layer causing damage below. In the case of roof terraces situated above living accommodation additional design considerations are required. To successfully tile a roof terrace both primary and secondary waterproofing should be installed to protect the internal integrity of the building. An architect or structural engineer should be consulted for full guidance.

The correct materials should always be used, including the bedding mortars and grouts, porcelain tiles and natural stone. Porcelain tiles should be classified and marked as suitable for external use in accordance with BS EN 14411. Natural stone should be marked in accordance with BS EN 12058.

Tiles should be selected with enhanced slip resistance. This is particularly important where tiling is laid to falls to allow water to drain away from potential wet areas. In external environments, tiles may heat up and cool very quickly compared to the background. This is particularly relevant where dark coloured tiles may be exposed continuously to direct sunlight.

Joints between porcelain tiles should be grouted with a suitable proprietary grout conforming to BS EN 13888 i.e. minimum CG2 or RG type grout. Exposure to greater thermal variation and moisture movement means that intermediate movement joints should be incorporated within the tile assembly at intervals not exceeding 3 metres. Depending upon the anticipated movement in the background, the size and format of the tiles selected and the width of the tile joints, the distances between movement joints may need to be less. Movement joints, in all cases should be continuous throughout the entire assembly, as outlined by British Standards.

Consideration also needs to be given to correct cleaning regimes, in order to maintain both the aesthetic appearance and the required slip performance. External tiled or stone finishes are likely to become contaminated more quickly from dirt and debris. High pressure washing is therefore often employed. Although this will not damage the tiles themselves, it may cause damage within the grout lines so should be carried out with care. Consideration should also be given to the use of a proprietary impregnating sealer and a bespoke tile cleaner.

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