Setting Over A Bad Slab Means You Just Bought It
Crew is mobilized, the container is on site, and the floor reads 3/16 in 10 feet. Everybody in the trailer turns and looks at you to make it work anyway.
Three conditions gate tile and none of them are yours. Flatness belongs to the concrete sub, while permanent HVAC and the calendar belong to the GC. ASTM F2170 in-situ RH probes can't go in until the slab has sat at service temperature and humidity for 48 hours, then need 24 hours to equilibrate, and your setting materials carry a 50 degree minimum that has to hold through cure. No other finish trade has its warranty, its start date, and its callback exposure all keyed to conditions somebody else controls.
The size of it
You get to the job mobilized with three bad options: eat $2-4 per square foot of self leveling underlayment, sit idle while the change order gets argued, or set over it and pay for lippage at punch. The only one you can bill for is the one where you documented the condition before you touched it.
ANSI A108.02 sets substrate flatness at 1/4 inch in 10 feet for tile with all edges under 15 inches, and tightens to 1/8 inch in 10 feet the moment any edge hits 15 inches or more. Every large format tile and every gauged panel being specified today falls on the tight side of that line. A concrete slab poured to ordinary ACI 117 tolerances misses 1/8 inch in 10 feet routinely, so the condition is normal and the standard still applies. The standard also says the installer shall not set over an out of tolerance substrate, which means the morning you set anyway, you accepted the slab and you own every bit of lippage at punch.
Three moves, in order
Step 06: Project management
Billing dates, change orders, and notices, run as standards that hold without anyone chasing them.
What else costs tile and stone contractors money
The same mechanism in other trades
What tile and stone owners ask
Who pays to float a slab that's out of tolerance for large format tile?
Crew is mobilized, the container is on site, and the floor reads 3/16 in 10 feet. Everybody in the trailer turns and looks at you to make it work anyway.
What does it cost?
You get to the job mobilized with three bad options: eat $2-4 per square foot of self leveling underlayment, sit idle while the change order gets argued, or set over it and pay for lippage at punch. The only one you can bill for is the one where you documented the condition before you touched it.
What do I do first?
Run a 10 foot straightedge across the floor before the crew unloads a single carton, and photograph the readings with the date and the room number in the frame.
What are tile and stone contractors supposed to be making?
Tile and stone runs 22% gross margin, 14% overhead and 8% net profit before taxes at $1M–$5M. The all-trade average is 7%, so this trade sits 1 points above it. The CFOS target is 10%.
Which part of the system fixes it?
The step is number 06, project management. Billing dates, change orders, and notices, run as standards that hold without anyone chasing them. It comes from chapter 6 of CONTROL: The Construction Financial Operating System.
Josh Luebker ran commercial construction projects before he ran the numbers behind them, on data centres, military bases, hospitals, and high-rises. He wrote CONTROL: The Construction Financial Operating System, which is an eight-step framework for commercial subcontractors, and it publishes on October 1, 2026. He is a master electrician who moved into the office and kept the field vocabulary.
Sulphur Prairie Operations LLC maintains the benchmark reference behind these figures. Every edition is reconciled against the newest CFMA survey release before it publishes here. Where a figure changes between editions, the older edition keeps its year in the title so a citation to it stays correct.