The washing and changing area, or auxiliary building, is situated along with the mining office on either side of the access area to the industrial site. The ground floor houses a fire station, offices, first aid room and boot-cleaning room, while upstairs there is a bathroom and changing room, in addition to a number of solariums.

The auxiliary building is made up of two spaces. The largest takes a rectangular form, is constructed of whitewashed concrete and is topped off by a lean-to roof bowed at the front. The smaller space is situated on the northwest side and has red-painted panelling on the upper floor, and the same-shaped roof as the larger space.