Setting times
Premix mortars contain a cement control-set admixture and will remain usable, when stored in the covered tub, for up to two working days. When used in masonry, they set like site mixed material and with equivalent performance.
The normal setting time depends on sufficient suction taking place from the mortar to the brick or block. If the unit is saturated, or worse still frozen, the bond is impaired and hydration of the cement will not take place for the full period of retardation Consideration should be given to local site conditions and the length of time that unpropped walls are vulnerable to collapse. Independent advice is available from the Mortar Industry Association.
After the initial set begins, Premix mortars should not be used or remixed with water. Reduced workability through evaporation may be restored by adding small amounts of water on the spot board and thorough hand-mixing. Further admixtures should never be added.