ᐅ Source cement with the finest grain size

Hello everyone,
for the renovation of thin joints 2-3 mm (0.08-0.12 inches) wide, I am looking for a cement with a maximum grain size of 1 mm (0.04 inches) that also swells or does not shrink during setting.
Does anyone have any suggestions?

The only thing I have found so far is a swelling or packing mortar with a 2 mm (0.08 inches) grain size.

A swelling grout mortar is not an option. The material should not flow away but remain in the joint.

Thank you

Can’t you just use grout that is also used for tiles? It has a fine grain and is available for both indoor and outdoor use.

This concerns a bed joint in the brick masonry that needs to be repaired. I don’t think joint mortar is the right material for this, is it?