Granite Tile Lippage Tolerance: How Big a Step Between Two Tiles Is Acceptable?
Granite tile lippage tolerance starts at 1 mm for interior polished work laid tight, 2 mm for exterior open-joint paving and 3 mm for rough thick slabs. Lippage is a result of laying, not a property of the slab: two tiles both inside a ±1 mm thickness tolerance can still leave a 2 mm step underfoot.
How much lippage is allowed on granite tiles?
Start with the three figures we use when we talk a job through with the site team: within 1 mm for interior polished work laid tight, within 2 mm for exterior paving with open joints, within 3 mm for rough finishes, thick slabs and large formats. These are starting points, not code values and not a pass line; the number that actually governs is the one written in your contract. Keep two ideas apart as well. Lippage is the height difference across a joint after two tiles are laid. Flatness is how level one tile is on its own, measured with a straightedge resting on that single tile, and it belongs to the dimensional tolerance sheet; we only mark the border here. Lippage needs a straightedge that spans the joint and touches both tiles.
| Case | Starting limit for lippage | What this number mainly governs |
|---|---|---|
| Interior polished, tight joint (countertops, floor transitions) | Within 1 mm | Factory thickness consistency + site laying |
| Exterior paving with open joints (plaza paving, footpaths) | Within 2 mm | Site laying, mainly |
| Rough finish, thick slab, large format (flamed driveway, 50 mm and up) | Within 3 mm | Site laying + base |
What adds up to make that step?
The step between two adjacent tiles is thickness difference plus support difference under the slab plus bow, and the three come from different places. Thickness difference is the gap between the two actual thicknesses: our 30 mm slabs are quoted at ±1 mm, so one at -1 and its neighbour at +1 give 2 mm = 1+1 at worst. Both passed inspection, and the step exists before anyone lays a tile. Support difference is the real thickness variation of the mortar or sand bed plus any void. It is not a factory variable: a void collapses the moment someone stands on it, so it belongs in the contract. Bow is the two slabs curving in different directions: thickness-calibrated slabs are flatter than uncalibrated ones, and a flamed face picks up slight bow after the rapid cooling, more so on thin slabs. Responsibility splits along the same lines: thickness consistency and bow belong to the factory, through same-batch calibration on one machine and slab selection; the bed belongs to the contractor, meaning bed thickness, full contact and compaction, and voids. Holding 1 mm by selecting slabs alone does not work, because the bed moves by millimetres. Order of work: bed first, thickness consistency second, selection last.
Why does a polished face show the step more than a flamed one?
A polished face carries reflection in one continuous line, and a 1 mm step cuts that line. Drop your eye to 15° above the surface and the shadow at the edge of the step measures about 1 ÷ tan15° ≈ 3.7 mm: a 1 mm difference is drawn out into a visible band, purely geometric and ignoring the grain, and the closer you get to eye level the worse it reads. A flamed or bush-hammered face has its own relief, and the texture swallows the step; you will not see it and may not feel it with a hand. Not seeing it is not the same as it not being there. Water follows the low tile, and the foot still drops at the joint. Sight can forgive it; inspection cannot, and the straightedge and feeler gauge still have to come out.
What do you measure with on site, and what does the reading mean?
Four steps, with the straightedge matched to the tile. One: wipe both sides of the joint clean, because a grain of sand lifts the straightedge and inflates the reading. Two: lay the straightedge across one joint with each end on a different tile, keeping at least 90 mm of overhang at each end so the tips do not sit on the 2 mm chamfer. The joint carries nothing because the straightedge bridges it, so size the tool as two tiles plus the joint plus overhang: a 300 mm tile takes an 800 mm straightedge, a 600 mm tile takes 1.5 m. A straightedge that only just equals two tiles lands both tips on the chamfer and the reading inflates; a short one sits on a single tile and you are back to measuring flatness. Three: push the feeler gauge along the straightedge into the joint mouth until it will not go further; that is the largest gap at the joint edge. Four: turn 90° along the joint and measure again, because each of the four edges of a tile can differ, and record the larger figure.
It is already there — grind it down or lift it out?
The high tile can be ground; the low one cannot be pressed down. Grinding within 1 mm is acceptable, but a polished face has to be re-polished on site afterwards. Leave it and you have a matte patch that draws the eye more than the step did. Grind 2 mm and a 2 mm chamfer disappears altogether: the joint edge goes from a rounded arris to a sharp right angle that chips on first contact. The low tile will not sink. Once the mortar has set, forcing it only cracks the slab, so it has to be lifted, the bed made up and the tile relaid. If a whole area has risen, that is not voiding: a void lets the tile settle underfoot, it does not push it up. A floor rises for two reasons only: joints left too narrow so thermal expansion has nowhere to go and the tiles push against each other, or no edge restraint so the field creeps outward. Grinding and bedding both fail here; relay it, and check joint width and edge restraint first, because relay without widening the joints or locking the edge and it arches again. Poor drainage gives you a hollow, settling base, not an arch. The costs differ: grinding is cheapest, lifting is priced per tile, relaying per area.
How should the order and the site briefing be written so the step never appears?
Put three lines in the order. Thickness: write the ceiling itself, that adjacent slabs in the same batch differ by 1 mm or less, and say it is measured at the same point with the same gauge. 30 mm ±1 mm governs one slab, not the pair; two slabs drifting opposite ways make 2 mm. Laying: tight or open joint, plus the nominal joint width. How to size that joint is not this article; it only has to be on the sheet. Acceptance: the tier, the method and who pays for rework. Method as a straightedge across the joint, two directions, feeler gauge reading; rework split between grinding, lifting and replacement. Then ask three questions at the briefing: did this batch come off the same calibrating machine; is acceptance measured across the joint or on single tiles; who pays for grinding, lifting and replacement. Our Sesame Grey G602 is kept in 30 mm slabs, calibrated batch by batch on one machine, 100 ㎡ minimum, 5 days to ship, 346 ㎡ to a 20 ft container.
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