Grout is tiles joint – small space – between tiles, this space function is to allow the craftsmen to align tiles together. Typically spaces between tiles range from 2 to 4 mm and it measured by plastic grout spacers.
The size of tiles joints can affect the tiles style either modern or classic. For modern appearance usually we recommend arrangement tiles directly with no space. This fit laser cut tiles case, where tiles are well trimmed at 90 degrees angles. On the other hand, saw cutting tiles will have classic appearance. Saw cutting tiles are cheaper than laser cutting tiles, but during manufacturing it could have a difference in tiles size. This could appear clearly by eyes therefore it’s better to use large tiles joint about 7 mm wide. However in classic appearance tiles it more beautiful to leave a large grout space, but be aware to buy a good brand ground to avoid color changing.
Grout function is to align tiles together and it’s not expansion joints, because it could fill by cement grout or in marble tiles cases could fill with epoxy or marble adhesive. Both fillers type could be colored to appear in harmony or in contrast with tiles.
As expansion joint we recommended to leave around a cm between tiles and walls. The expansion joint will cover by tiles’ skirting. Expansion joints need to be clear from sand and mortar, then to fill with highly stretchable material like Sikaflex. Then it covers with tiles skirting.There is a special accessory for tiles expansion joints where it installed outdoors in high temperature countries.
According to ISO standards 13007, where grout classified according to materials to resin grout RG and cement grout CG. The cement grout classify to CG1 and CG2, of course CG2 is better. You can search about Iso standards 13007 for more information. Notice that there are few other factors affect grout quality. For example, the tile joint has to be clear from sand or dust, so the grout find a place it self.