What is tile lippage?

Start with the floor nobody sees

Lippage starts before a single tile is set, with the subfloor. Every subfloor has some amount of unevenness, a slight hump here, a shallow dip there, left over from framing, from an old floor's residue, or simply from how concrete cures. Subfloor prep is what closes that gap before tile ever goes down, and it is the single step in this sequence that decides how much lippage risk the rest of the job inherits.

Then the tile itself, which is never perfectly flat

Every manufactured tile carries a small amount of built-in variation, a slight bow or warp across its face that comes from the firing process rather than from any defect. It is normal, and every box has some of it. An installer sorts through it as tiles are pulled, turning a slightly bowed piece so its high point works with its neighbor rather than against it, a judgment call made one tile at a time rather than something a bag of thinset can fix on its own.

This is also why opening more than one box before setting a floor matters. Warp and shade can both drift slightly from one production run to the next, and mixing tile from several boxes as the floor goes down spreads any of that variation evenly across the room instead of letting one box's slightly bowed run land together in one corner where it would be far more noticeable.

The thinset bed does the leveling, or it does not

Thinset is not just glue, it is also the layer that absorbs the small differences between the subfloor and the tile above it. A trowel notched for the tile size builds ridges of mortar that collapse flat as the tile is pressed and worked into place, called back-buttering when it is also applied to the back of the tile. Skimp on that step, rush the working time, or use a trowel notch too small for the tile, and there is not enough mortar under the tile to absorb the variation already present in the subfloor and the tile itself.

Leveling systems, and the step most jobs actually lean on

For larger tile especially, installers commonly use a leveling clip and wedge system that physically pulls two adjoining tile edges into the same plane while the thinset is still soft enough to move, then gets snapped off once it has set. It is a mechanical answer to a problem that used to be solved by eye and by hand alone, and on a tile with any real size to it, it is often the single tool that decides whether the finished joint sits flush or catches a fingernail.

The step that decides the outcome

Of everything in this sequence, substrate flatness matters most, because everything downstream is compensating for it rather than starting from zero. A tile bed that has to absorb a hump in the subfloor has less mortar left to also absorb the tile's own slight warp, and a leveling clip can hold two edges flush to each other without making either one flush to the floor as a whole. Get the substrate flat and the rest of the sequence has an easy job. Skip it and every later step is working around a problem it did not create.

Which tile makes the risk bigger or smaller

Tile size and format change how forgiving this whole sequence is. A larger tile has a longer face for a subfloor's unevenness to show up across, which is why large format tile asks more of the substrate before it ever gets set. A smaller tile, or a pressed-edge tile with a wider grout joint rather than a tight rectified one, gives the eye more places to break the sightline and hides a small amount of lippage the way a large plank cannot. If the existing subfloor cannot be made perfectly flat without real cost, that is worth weighing against tile size before you order, and it is exactly what the free in-home measure checks before anything is ordered. Call 636-332-0654.