Without some degree of surface preparation, it’s highly unlikely that a concrete slab or wood-framed subfloor will be flat enough to meet the requirements for large-format tile. A quick check with a straightedge often shows that a small area or perhaps the entire surface dips and undulates outside of industry standards. The resulting lippage, an unsightly variation in height between tile edges, shows up very quickly with today’s large-format tiles. Because of the difficulty in laying 24-, 36-, 48-inch and up to 10-foot tiles without lippage, contractors regularly use leveling clip systems to hold tile edges flatly together while mortar cures. If the substrate isn’t flat before you start, the installation requires more labor and there’s a greater chance that the completed installation will be rejected.
Some tile contractors attempt to level tiles — even very large tiles — using adhesive mortars. Forensic consultants and manufacturers’ reps don’t see a week go by where an installer hasn’t used the “spot bond” or “5-glob Bob” method as a shortcut to failure. This practice is actually becoming a serious industry problem as many untrained and low bid contractors are entering the trade and not accounting for proper surface preparation. Unfortunately, once they start the project, the cost and burden of “leveling tiles” falls to them instead of the building owners.