Can Type III portland cement be used in mortar during warm weather?
In general, mortars made with Type III portland cement are not ideal for summer work. Type III portland cement mortars hydrate faster than mortars made from Type I portland cement. The faster the cement hydrates, the more heat is generated. The greater the temperature, the faster the mortar will set. However, you might consider using Type III portland cement in warm weather, if the masonry work will be continuing into the winter months. That way, you can avoid changing the mortar mix part way through the project and risking a change in mortar color. Be aware, though, that masons would then have to deal with the mortar's shorter board life. You can minimize the problems by mixing mortar with cool water, mixing smaller batches, and keeping units cool.