Eight flats in a new building, handed over with a builder's clean that had taken out the rubble and left everything else.
We did it in three passes over four days. The first took out the bulk. The second, the day after, took the fine plaster dust that had settled out of the air overnight, which is the pass most people skip and the reason a new flat keeps looking dusty for a month. The third went through the window channels, the air grilles, the electrical boxes and the tops of the doors.
The landlord had two flats let within the week. He has since sent us two more buildings, and on both of them we were booked before the contractor finished rather than after.
