In my experience the technical knowledge displayed by British and Irish tilers is quite poor. Most tilers here are self taught compared to the rest of Europe, where the skill levels seem to be much higher due to specialised courses. With this in mind, it is good to know the most common pitfalls and check these for yourself.Over the years I have been asked to investigate many areas of badly cracked tiles and to advise on the cause. The most usual reason behind many of these damaged surfaces were technical errors. Those errors resulted in costly repair work, replacement of tiles and even court cases. Problems with tiling seem to be more common in domestic projects (especially self-builds) compared with the larger commercial projects where usually either a more experienced tiller is used or there is a supervising engineer/ Clark of works present to check work.
So if you are employing a tiler, here is a checklist for the most common mistakes they can make when laying floor tiles:
- Tiling on timber floors. When laying tiles on a suspended timber floor, the floor should be strengthened to reduce movement which otherwise will crack the tiles. The easiest way to achieve this is by screw fixing a thick layer of marine plywood (18 or 25mm fixed at 300mm c/c) to the floor prior to tiling. Remember to check the subfloor is sound first with timber bridging in place and no defects. The tiles should then be laid on flexible adhesive. Flexible adhesive will not usually be sufficient on its own to prevent cracking.
- Tiling in wet areas. If tiling in a wet area (shower wall, wet room etc) a gypsum plaster board cannot be left in place unless it is waterproofed prior to tiling. However in my opinion it should be removed and replaced with a layer of marine plywood or moisture resistant green board. These boards should then be ‘tanked’ by coating with a suitable brush on waterproof membrane. This is available from a good tile supplier and is usually applied to a depth of 2 to 3mm in a number of coats. After the tanking membrane has dried sufficiently the tiles should be installed using waterproof grout.
- Consider the surface resistance (grip) of tiles. Use a tile with a level of surface grip which is suitable for the location. For example a tile laid in a wet area or at the top of a stairs will need to have more surface grip to prevent persons slipping and causing injury. Note some areas which seem dry may not be dry all the time, for example the entrance areas of properties will probably have a wet floor after heavy rain or snow showers as people entering will bring water into the property on their footwear.
- Tiling at joints in slabs. Large ground bearing concrete slabs require joints to allow the slab to expand and contract without cracking. Any tiles laid on the concrete slab will require joints to follow the same line as the joints below otherwise the tiles will crack at these points. A particular place to watch out for this is at room junctions where a ground bearing concrete floor is continued through the door way. This part of the floor slab will be supported by the rising wall while the reminder will be supported on crushed stone. Over time the crushed stone underneath the room floor is more likely to settle than the rising wall which is supported by a deep foundation. The concrete floor is likely to bend at this point and crack the tiles above. A joint should be provided at this location, it can be hidden as necessary by using a threshold covering piece (a saddle board).
- Provide joints in the tiled area. To avoid cracking and/or delimination of the tiled surface, expansion joints are necessary in tiled floors. This is to allow for the stresses caused by heating and cooling and also for slight structural movements which would cause damage to a brittle floor tile. This is especially important if the floor has underfloor heating. The British Standard, BS 5385:Part 4, advises that expansion joints should be provided in a tiled floor with underfloor heating at a maximum of 3.5m centres with isolation joints around the perimeter of the tiled area. Where underfloor heating is not present the recommended distance between joints in the concrete floor screed is between 5 to 6m, with joints extending through the tiled surface. But bear in mind that the above will vary depending on the type of tile used i.e. a large tile composed of a natural stone material will probably crack quite easily compared to a small strong engineered tile. Unfortunately the large natural tile is usually more expensive to replace.