A customer in an older part of Durham called me a few months back about a bathroom floor another crew had finished. Nice tile. 12×24 porcelain, the gray woodgrain look that shows up in about a third of the bathrooms we quote now. The problem was that you could feel the edges with your bare feet, and once the morning light came through the window at a low angle, you could see a shadow line under every single tile edge running along the wall.
That is lippage. And it is the single most common complaint I get about large-format tile in this town.
The frustrating part is that the tile was fine and the guy who set it probably worked hard. The floor underneath was the problem, and nobody looked at it before the thinset came out of the bucket.
What lippage actually is
Lippage is the height difference between the edges of two tiles sitting next to each other. One tile sits a little proud of its neighbor, and you get a lip.
There is an actual standard for this. The Tile Council of North America publishes the allowable limits from ANSI A108.02, and they are tighter than most people expect. With a grout joint between 1/16 inch and 1/4 inch, allowable lippage is 1/32 inch, plus whatever warpage the tile itself came with from the factory. Go to a 1/4 inch joint or wider and you get 1/16 inch.
A 32nd of an inch is about the thickness of a credit card. That is the whole budget.
One thing worth clearing up, because I have heard installers get this wrong: the tile’s allowable warpage does not get added to your budget. It is the tile’s actual warpage that counts. If you buy a batch of large-format porcelain that is bowed right up to the edge of what the manufacturer is permitted to sell, you have almost no room left before the floor reads as uneven. That distinction matters when someone is arguing with you about whether a floor passes.
Why large format makes everything harder
Two reasons, and they compound.
The first is warpage. Tile is fired in a kiln and it does not come out perfectly flat. Manufacturing standards allow a percentage of the edge length, which means a 24 inch tile is permitted to bow roughly twice as much as a 12 inch tile in absolute terms. The tile is not defective. It is just longer, so the same percentage buys more curve. Set a slightly domed 12×24 next to another slightly domed 12×24 and their corners physically cannot all land in the same plane.
The second is that a long tile bridges a longer stretch of floor. A 12×12 sits in a small dip and barely notices. A 24×48 spans it and tips.
This is why the flatness requirement gets stricter as tiles get bigger. For tile with any edge 15 inches or longer, the substrate has to be flat within 1/8 inch over 10 feet, and within 1/16 inch over 24 inches. Under smaller tile you get 1/4 inch over 10 feet. That is a big jump in tolerance, and almost nobody selling you tile at the showroom mentions it.
The Durham part
Here is where our housing stock comes in.
We work in a lot of 1940s bungalows, mill houses, and the older streets around Trinity Park, Forest Hills, and Watts-Hillandale. Those houses have been settling on brick piers for eighty years. Joists sag toward the middle of the span. Piers sink at different rates depending on what the crawlspace soil has been doing. Bathrooms got added in the 60s over joists that were never sized for a cast iron tub, let alone a tub plus tile plus mortar.
Then there is the subfloor itself. A lot of these homes have 1x board subfloors laid diagonally, sometimes with a layer or two of old flooring on top of that. Boards cup, shrink, and telegraph every seam. I have pulled up bathroom floors in Durham with four layers of history in them: original boards, sheet vinyl, a plywood underlayment somebody added, then vinyl again.
None of that was a problem when the finish floor was linoleum or 4×4 ceramic. It becomes a very visible problem the moment you put a 24 inch tile across it.
Newer subdivisions have their own version. The slabs and engineered joist floors out toward Southpoint and Brier Creek are usually flatter to begin with, but builders work to framing tolerances, not tile tolerances, and a long open-plan kitchen can still wander an eighth of an inch or more between the island and the pantry.
So when someone in an older Durham home tells me they want 24×48 in the kitchen, my first thought is not about tile. It is about how much floor prep this house is going to need, and whether the budget has room for it.
The pattern nobody wants to hear about
Almost everyone who walks in with a 12×24 tile wants it laid in a 50 percent brick offset, like a running bond brick wall. It looks great in the showroom photo.
It is also the fastest way to get lippage, and the standard says so. For tiles where the offset side is longer than 15 inches, ANSI limits you to a 33 percent offset unless the homeowner signs off on a mockup first. The reason is simple geometry: at 50 percent, the high point in the middle of one warped tile lands exactly at the end of its neighbor, which is the tile’s low point. You are stacking the two worst spots against each other on purpose.
Drop to a third, or a quarter, and the mismatch drops with it. Herringbone gets even more forgiving because the joints are short. I bring this up at the estimate, not after, because it changes what the floor is going to look like and people deserve to make that call themselves.
Grout joint width plays into it too. Everybody wants a hairline joint. If your tile is calibrated rather than rectified, meaning the edges came out of the kiln as-fired instead of being ground square afterward, the standard wants at least a 3/16 inch joint. A wider joint gives the eye a gradual step instead of an abrupt one, and it gives us somewhere to hide the difference. A 1/16 inch joint under a warped calibrated tile is asking for trouble.
How we actually prevent it
This is the part of the job that costs money and that nobody sees when it is done right.
We map the floor before anything else. A long straightedge and a laser tell us where the high and low spots are, and we mark them on the subfloor in pencil so we can see the shape of the problem. In an older bungalow this usually looks like a slow dip toward the center of the room with a hump over a joist or two.
Then we fix it. Depending on how bad it is and what is under there, that means self-leveling underlayment poured over primed plywood, patching compound feathered into localized dips, or in the worst cases sistering joists in the crawlspace before we do anything on top. Self-leveler is the workhorse for us in these houses. It is not cheap and it adds a day, and it is also the difference between a floor that passes and a floor you argue about.
When we set, we back-butter every large tile so there are no voids for a corner to settle into, and we use leveling clips through the field. Clips are not a substitute for a flat floor. Plenty of installers treat them that way and it does not work, because a clip can pull two adjacent edges even while the tile as a whole sits at the wrong height. They are the last 10 percent, not the first 90.
Before we grout, we kill the overhead lights and put a work light down at floor level shining across the field. Raking light is brutal and it is exactly what your kitchen window is going to do at 7am. Anything that shows up under that light gets pulled and reset while the thinset is still workable. Anything that only shows under a light we invented is usually fine.
One more thing we do that is more conversation than craft: if a customer picks a highly polished large-format tile for a room with a big east-facing window, I tell them what that combination does. Gloss plus low-angle light will show variation that a matte tile would hide completely. Some people change their mind. Some people want the gloss anyway, which is a perfectly reasonable choice as long as they made it with the information.
If you already have lippage
The honest answer depends on how much and where.
If a few tiles are proud and the rest of the floor is flat, we can sometimes pull and reset just those. If the edges are sharp enough to catch a toe or a chair leg, that is a safety issue and worth fixing regardless of how it measures.
If the whole floor moves, the substrate is the problem and resetting individual tiles will not hold. Rework in that situation means demo down to the subfloor, prep it properly, and start over. Nobody enjoys hearing that. I would rather tell you than take your money to patch something that will look wrong again in a month.
For a floor that is within standard but bothers you under certain light, there is not a repair. There is only a conversation about expectations, ideally one that happens before the tile is ordered.
Frequently asked questions
Is some lippage normal in a tile floor? Yes. The standard allows about 1/32 inch with typical grout joints, plus the tile’s own warpage. A floor with zero measurable height variation anywhere basically does not exist. The question is whether it is within tolerance and whether you can feel it.
Does large-format tile always have more lippage than small tile? Not always, but it is much less forgiving. The same subfloor imperfection that a 6×6 sits over will tip a 24×48. Large format is not the problem. Large format over an unprepared floor is.
Can leveling clips fix an uneven subfloor? No. They hold adjacent edges together while the thinset cures, which helps with minor variation. They cannot correct a floor that is out of plane, and using them that way tends to produce a floor that is flat in small patches and wavy overall.
Why does my tile look fine at night and bad in the morning? Light angle. Overhead lighting hits the floor near vertical and hides height variation. Low sun through a window rakes across the surface and casts a shadow off every edge. This is a known factor in the ANSI standard, and it is why we check with a raking work light before grouting.
How much does floor prep add to a tile job in Durham? It depends entirely on what your floor looks like when we pull the old surface up, which is why we do not quote it over the phone. Prep is the line item that varies most from house to house. We break down how tile pricing works, prep included, in our Durham tile installation cost guide.
Do you have to replace the whole floor to fix lippage? Sometimes, sometimes not. Isolated high tiles can often be pulled and reset. Widespread lippage usually traces to the substrate, and that means starting over. We will tell you which one you have after we look at it.
Get a look at your floor before you order tile
If you are planning large-format tile in an older Durham home, the useful time to have this conversation is before you buy material. We can tell you what the subfloor is going to need, what pattern will work with the tile you like, and what the prep is going to cost.
We handle tile installation across Durham and the Triangle, including floors, backsplashes, showers, and repairs to work somebody else left behind. If tile is part of a larger project, our flooring crews in Durham and Raleigh are the same people, so we can scope the whole thing at once. Deciding between tile and a plank floor for a kitchen or bath is a fair question too, and our take on luxury vinyl plank covers where each one makes sense. When the work is done, our cleaning team can come through so you are not living in dust for a week.
Vilchis Hardwood Floors & Tile 237 Obie Dr, Durham, NC 27713 (919) 794-1116 Monday to Friday, 9:00 AM to 5:00 PM
Serving Durham, Raleigh, Cary, Chapel Hill, Carrboro, and Wake Forest. Free in-home estimates, written fixed-price quotes.
