Tile sizes always vary slightly. Here’s an explanation why.
Natural stone tile dimensions are subject to certain allowable size tolerances. This is on the thickness and on the overall dimensions of the tiles. Most of the natural stone tiles we sell have what is known as a “rectified” edge. This is a square cut edge with a sharp corner to the surface of the tile. Polished/honed marble tiles, honed travertine tiles, honed/polished limestone tiles and polished granite tiles all have a rectified edge as do our quartz tiles. The only stone tiles that don’t have a true rectified edge are our tumbled tiles as they have what is known as a “tumbled edge”. These started out life as rectified, but have been through an ageing process to give them that worn aged look that rounds off the edge of the tiles.
In the process of making rectified natural stone tiles, large slabs are cut from blocks of stone and these slabs are then cut into tiles. Modern machinery has made it possible to cut the tiles to very close tolerances, usually 0.5 of a millimeter. Tiles that do not meet acceptable tolerances are picked out by the factory's quality control inspectors. 0.5 of a millimeter doesn’t sound like a lot, and in manufacturing terms it is quite acceptable.
How size affects installation
Where people have problems with the sizes of their tiles is when they have seen a floor laid with practically no grout joint and they want the same. Unfortunately, when they tell their tiler that this is what they want, apart from the tiler groaning about it (as it’s really difficult to achieve) the end result generally doesn’t turn out how they had wanted or expected.
It is not recommended to install natural stone tiles tight up against each other for two reasons:
The tolerance on the dimensions of the tile means that you will never get all the tiles to line up exactly on the corners, especially if you are laying the tiles in what is know as “stack bond” where the tiles are laid row by row directly on top of each other. The 0.5mm tolerance on two tiles next to each other could add up to a difference in 1mm over the two tiles, and 2mm over 4 tiles in a row. What people don’t see when they have seen floor tiles or wall tiles laid like this is the fact the joints don’t line up as they only see the overall look that is achieved from a completed room. It’s only when they get into the tiling and everything is examined under a microscope that this comes to their attention. Aside from anything else, tiling a floor like this is an expert job and should only be undertaken by somebody with vast knowledge of installing natural stone tiles.
All tiles whether they are porcelain, quartz or natural stone should have a minimum of 2mm grout joint to allow for very minor expansion and contraction of the tiles under different temperature conditions, especially with underfloorheating. Modern grout and adhesive is flexible and allows for this. Laying tiles tight up against each other without joints can sometimes lead to cracking or warping in the case of quartz.
A good tiler will know how to take into account the slight variations in width and height of a tile by adjusting each joint and row as they go along. Once the tiles are grouted, the customer will never see the tiny variations in the size of one tile next to each other if the tiler has done a good job. It’s only when you get inexperienced tilers that, for instance, try and use the cross shaped tile spacers in the corners of the joints that you get issues, and they often blame the quality of the tiles as they aren’t used to installing natural stone.
Porcelain tile size variations
Porcelain tiles are a slightly different story. The manufacture of porcelain tiles starts out with a combination of various materials in dust that are pressed into a mold under high pressure then fired in kilns. The finished product is a tile in the shape of the mould. Porcelain tiles are often sold straight from the mold and have a slightly angled edge, the same shape as the mould - known as a natural edge or moulded edge. The tolerance to European standards on these kinds of tiles is up to 3mm. They don’t normally vary this much but these are the tolerances that are quoted. As such, a joint width of 3-5mm is recommended for natural edged porcelain.
Porcelain also comes rectified like natural stone. This is where the tiles are processed through machines that trim the edges off the tiles leaving a sharp, square rectified edge. The tolerance on the machines cutting these edges is very small indeed, making each tile practically the exact same size as the next one. As with rectified natural stone tiles, there is always a tolerance but that should be more like 0.2mm. Even with rectified porcelain tiles, it’s not recommended to install these with less than a 2mm grout joint as discussed above.
Tile thickness variations.
Natural stone tiles will often vary in thickness as well. +/-1mm is acceptable and any decent tiler will be able to take this into account by adjusting the tile in the bed of adhesive to suit. If a tiler complains about the varying thicknesses of tiles that are within this tolerance, then they are probably trying to deflect attention away from the fact the tiles they have laid aren’t all flush with each other and you have what is known as "lippage". Lippage is only ever down to poor installation and nothing else.