Objects placed in the outside world will now decay over time. Likewise they can be repaired. The object will inform you of what it needs for repairs.
Constructions (kilns, ovens, smelters, and houses [when decay is implemented for them] etc.) should be built on paved stone tiles. You can still build them on open ground, but they suffer 4x the normal rate of decay if you do. Also, objects decay 2.5 times as fast in Mordor as they do at the RoB, or equivalent