To what extent is it permissible to build a separate mosque for workers and prevent them from praying in the administrators' mosque due to the smell of sweat, and does that affect the validity of prayer in both mosques?

Preventing those with offensive odors from attending congregational prayers in mosques has a legal basis in Islamic law. It is forbidden to approach the mosque for one who has eaten garlic or onions; rather, it has been commanded that one from whom the smell of onions and garlic is found should be expelled from the mosque.

It is disliked for one who has eaten garlic, onions, or radishes, and the like, to attend the mosque until their smell departs. This also applies to anyone who has a foul odor that causes discomfort to others.

The ideal solution for this issue is either to instruct them to bathe and change their clothes whenever they wish to enter the mosque, or to designate a place for them to pray in congregation.

Two congregations in two adjacent places have no effect whatsoever on the validity of the prayer, and this is in cases other than the Friday prayer.