SET TIME
The elapsed time after mixing whereupon the mortar begins to harden is the set time. This test is most commonly performed on cement paste (cement + water), but can also be conducted using mortar. The test is completed by measuring the penetration of a steel needle into the paste or mortar over the course of several hours. The needle is part of an instrument called a "Vicat apparatus". When the penetration of the needle into the material is less than 25 mm for paste or 10 mm for mortar, the material has achieved its "initial set". The time required to achieve this degree of hardening is reported as the test result.