Note that using the smallest grout possible will increase installation time.
Grout joint size for wall tile.
Finished grout lines will vary from 1 16 to 3 16.
The tile council of north america and accompanying tile organizations recommend an average grout joint.
The grout joint size for 12 inch porcelain tiles recommended size.
Actual finished grout spaces will vary from 1 8 to 1 4 if 3 16 spacers are used.
Rectified tiles are any man made tile such as porcelain and are specifically designed to have as.
For example if the edge warping of a rectified tile is 1 32 the minimum grout joint is 1 8 1 32 5 32.
For example grout will discolour over time so keeping the joints smaller will minimse this issue.
For cementitious grout joints smaller than 1 8 generally should only be grouted with unsanded grout and joints of 1 8 and larger should only be grouted with sanded grout.
Not only does it look better to have smaller joints it also can minimise issues.
Joints larger that 3 8 usually need a more heavily sanded grout to accommodate the large joint.
However for example a 1 5 mm variation in a grout joint between 3 mm and 5 mm would not be noticeable.
Daltile recommends that large tiles have a 1 8 or 3 16 minimum grout joint for the most successful installation.
This thickness leaves room for the natural variation in size and the perfectly imperfect edges of handmade tile.
Often we see 1mm grout joints between wall tiles and 3mm grout joints between floor tiles.
All ceramic and stone large format tile greater than 15 requires a minimum 1 16 grout joint according to ansi.
They also suggest adding to this width the amount of edge warping on the longest edge.
A higher quality tile could allow for a 1 16 or 1 8 grout line and maybe even a brick layout as lippage may not be an issue in a perfect tile world where as a lower quality tile might have major lippage risk so laying the tile in 1 3 s and having a 1 4 grout line is recommended.
Ideally your grout joints would be 1 3mm.
For rectified tiles as as3958 1 gives no guidance to joint size then the manufacturers recommendation should be referred to.
The wider spacing will help to accommodate placement of tile and maintaining straight lines.