Refractory Mortar Particle Size: Why the Sieve Fractions Matter
Read maximum grain size and fine fractions together when specifying mortar for refractory brick joints.
Two mortars can show the same maximum grain size and still feel different to the mason. Their finer particle fractions influence spreadability, water demand, and how consistently a thin joint can be formed. A grading specification is therefore more informative than one top-size figure.
Read both ends of the distribution
The maximum size limits the coarsest material. A separate limit for particles above a sieve size controls oversize grains, while a minimum fine fraction describes how much fine material must pass a smaller sieve. Check whether the stated values are by mass and which test method applies before comparing suppliers.
Match mortar to the brick and joint
The mortar must be compatible with the brick chemistry and service conditions. Do not add water merely to force a coarse mix into an unusually thin joint. Prepare a small trial with the intended bricks, observe working time, and follow the grade-specific setting and heat-up instructions.
The Royal Set 45 technical sheet publishes both maximum grain size and sieve fractions for brick-jointing review.