The tiles were laid, the distance between the tiles was 4 mm.
When I cleaned the tiles, I noticed that the joints were uneven. How can I correct this so that the seams are more or less the same everywhere?
Consider 3 options:
1. Wet sponge with a hard side.
2. Sand with emery cloth.
3. Сoat again with liquid grout.
The joints can only be smoothed mechanically; with a flat screwdriver, a knife, i.e. clean out the tile joints and grout them again.
Grout the tiles after 3 days after laying. Grout a small area of the tile with a soft rubber spatula. After 10 minutes, run a dry finger horizontally and vertically over the seams and then carefully go into the corners of the tiles (overlapping only +/ leveling with straight lines). So grout the entire tile. The joints must be smoothed immediately after grouting the tiles, because even after an hour it is difficult to smooth the joints. Remove the remains of the grout with a dry, soft cloth, making sure that no small grains of sand remain in the joints.
Then wash the tile. Try it, but be careful in the corners of the tiles.
Do not use a sponge, it leaves traces on the grout and loses its fibers. You can carefully run a damp finger over it when some time has passed.
I recommend a fine sandpaper or the shaft of a drill (with a suitable diameter). This is mechanical scraping. Do not damage the tile.
Here is my experience of what not to do. In such a situation, we decided to rework the joints above the old grout, and now everything is cracked. It is better to clean them and do everything again.