Plus a 1 16 gap allows the caulk to properly fill the space and waterproof the transition between the tile and tub or shower.
Gap between shower floor and wall tile.
If your gap is smaller than 1 8 inch in width use regular caulk.
Soak a sponge in water and wet the tile with it.
As with any other gap near your bathtub you ll want to close the opening to prevent any possible water damage or the onset of mold and mildew.
Solution would be to partially fill the gap about a half way with grout and to finish of read seal remaining with commercial grade 100 silicone caulk.
Or fill the gap with grout.
This joint should then be filled with 100 silicone to allow for expansion and contraction as well as providing a waterproof layer.
Grout is generally the best choice for filling joints between tiles in showers or elsewhere.
Some like to use a ledger or other space saver to indicate where your missing row should be.
Another option would be to fill the gap with grout.
Similar to the gap that can exist between your wall tile and tub you may have a space between the floor and your bathtub.
And after installing the floor tile you can install that final or first row of wall tile.
This gap may widen over time as your home shifts.
Since you are joining two different materials together you should use caulk in the space where the floor tile and tub meet.
However due to different rate walls and floors expand grout will eventually crack again leaving you with the new hairline crack.
Fill gaps larger than 1 8 inch.
If you have tile on the wall adjoining the tub select a caulk that matches the color of the grout.
But where two tiled shower walls meet or where a shower wall meets the floor called change of.
Leaving a 1 16 gap between the tub and tile will prevent the tile from cracking when the tub expands.
Place the 1 16 horseshoe shim on tub and measure up to the laser level.
In addition leave a 1 16 to 1 8 expansion joint between the main wall tile and shower floor tile or adjacent wall tile.
Grout the gaps between the wall tiles take out the spacers and prepare the sanded grout mixture.