Masonry shower - opening for: glass blocks - alternative?

Hello everyone,

we would like to make a recess in a tiled shower and install glass blocks there.
But how big should this recess be?

The glass blocks are 20x20 cm in size.

Could I simply put 4 blocks into a 40 x 40 opening and grout it, or do I need that aluminum frame which would add another 0.5 cm on each side?

What would be the alternative? Or just not build the shower all the way up to the ceiling?

Thank you very much,

haunt

Hello,
so if I understand correctly, you want to insert the glass blocks into the masonry side wall. If the blocks are each 20 x 20 cm in size, the hole must be about 43 * 43 cm so that you have a joint thickness of 1 cm each. If the joints are to be narrower, the hole must be adjusted accordingly. But with exactly 40 * 40 cm, you will not get the blocks watertight and neatly installed.