Mortar and grout are not interchangeable fillers. Mortar bonds or beds masonry and tile in a specified assembly. Grout fills joints between installed tiles or masonry units. The correct formulation depends on the substrate, tile or masonry, joint dimensions, exposure, and installation detail.
Use each material for its intended job
| Task | Typical material |
|---|---|
| Bond tile to an approved substrate | Thin-set mortar meeting the tile and substrate requirements |
| Fill tile joints | Cementitious, ready-to-use, or epoxy grout approved for the joint and exposure |
| Movement or change-of-plane joint | Flexible sealant specified for the assembly |
| Build or repair unit masonry | Mortar type selected for the units and exposure |
Do not use extra mortar to correct a substrate beyond the product’s thickness limit, and do not use grout as a structural patch. Large-format tile, natural stone, showers, exteriors, and submerged work can require specific mortars, membranes, cure times, and movement joints. The tile, setting-material, and waterproofing instructions must agree.
Diagnose before regrouting
Cracked grout is often a symptom. Movement, poor mortar coverage, a flexible subfloor, missing movement accommodation, or water intrusion may need correction first. At a tub edge or inside corner, backer rod and sealant sizing may be more relevant than another rigid repair.
Before mixing, record the product’s water ratio, pot life, open time, working temperature, joint limits, cure time, and cleaning procedure. For sealing schedules after the repair, see grout sealer cure time .