We always recommend to store FibroTech indoors. Remove all plastic and distribute the boards with small sticks between each plate, so they can acclimatize. Let them acclimatize slowly and avoid using alternative solutions such as a heat gun.
Let the plates adapt to the room's temperature and humidity before you start mounting. To prevent the plates from contracting, do not mount the plates until the building work is completely done. Let it be painted too, as paint can release moisture for the plates to absorb.
FibroTech is oven-dried from the factory, but may have been exposed to external influencing factors that cause the plates to absorb moisture, and thereby have the risk of shrinking after mounting. FibroTech slabs must be stored horizontally on a pallet or a minimum of four joists.