Tiling a Commercial Kitchen Floor

The Floor Is a Drainage Surface First

Before it is a tiling job it is a drainage job, and the order matters because everything above the falls is shaped by them. Water leaves a kitchen the way the drainage layout intended or it sits in the low spot where the fat collects, which is the puddle the inspector photographs. The gradient is a specification figure — it belongs to the drainage design and to whoever signed the drawing, not to a rule of thumb you carry between jobs — so get the layout, mark the gullies and the channel runs on it, and establish which area drains to which point before you price a single bag of anything.

The most expensive thing to discover late is a gully set to the wrong level. A two-part kitchen gully has a lower body cast into or cored through the slab and an upper frame adjusted to the finished floor, with a flange the waterproofing clamps into and weep holes that drain the bed above it. If the drainage went in against a slab datum rather than a finished-floor datum, that frame sits thirty or forty millimetres low and no tiled floor arrives at it correctly. Check the frame height against your intended build-up on the first day you have access, while it is still a plumber's adjustment rather than your problem.

Then survey what the slab actually does, which is frequently not what the drawing says. Run a straightedge and a level out from each gully in several directions and mark anywhere the fall runs flat or backwards; that is fill you are buying, and it is worth knowing the volume before you promise a price. The arithmetic is simple once the gradient is fixed: a three-and-a-half metre run at one in eighty needs forty-four millimetres at the high point of that catchment, and because the screed falls to the gully from every side, tapering to nothing there, its average thickness across the area is two-thirds of that, not the half a one-way fall to a channel averages. Nine square metres draining to one gully at that depth is about two hundred and sixty litres of screed, a little over nine cubic feet — for one catchment. A kitchen with a channel and two floor gullies has three of them, and you take each one separately rather than smearing an average over the whole room.

Flatness still applies inside the fall. BS 8204-1, the code of practice for concrete bases and cementitious levelling screeds, sets the surface regularity classes a screed is specified to, and a floor laid to falls is held to one along the plane of that fall. Mark two more things on the sketch while you are down there: the dead areas under fixed equipment, where a lazy fall never gets washed clear, and every doorway and walk-in threshold, because a fall running towards a cold room door delivers dirty water to the one place nobody wants it.

1. Get the drainage layout and mark each gully, channel and its catchment area on it before quoting.
2. Measure the frame height of every gully and channel against your intended finished floor level, not against the slab.
3. Straightedge out from each drain in four directions and record where the existing fall is flat or reversed.
4. Fix the gradient from the specification, then convert each catchment's longest run into a maximum screed depth.
5. Take the screed volume catchment by catchment and add them, rather than averaging a depth across the whole floor.

What Sits Between the Tile and the Slab

An old kitchen slab is a contaminated slab. Fifteen years of fat has soaked into the concrete surface, and it does not come out with detergent and a mop, because the problem is not on the surface — it is several millimetres into it. Mechanical preparation is the only honest answer: shot blast or scarify back to sound, clean, open concrete, then check that what you have exposed will actually take a bond. Where the slab itself is the question rather than its surface, ACI 302.1R, the Guide to Concrete Floor and Slab Construction, describes what it was meant to be, and the service-rating language a specification uses for this duty traces back to ASTM C627 and its Robinson-type floor tester.

The layer that separates a kitchen floor from a shop floor with quarry tile on it is the bonded waterproof membrane. Neither the tile nor the grout is a waterproofing layer: quarry tile is a fired ceramic with real water absorption, and a resin grout joint is a seal at the surface and nothing below it. Bonded, load-bearing waterproof membranes for tile are specified to ANSI A118.10, and the specification is the easy part. The detailing is what fails — the membrane has to be dressed into the gully flange and clamped, carried up behind the coved skirting to above the highest point washdown water and steam reach, and taken continuously through every pipe penetration and equipment leg rather than stopped at them and sealed with something hopeful.

Liquid-applied membranes suit this geometry better than sheet for most kitchens: a floor laid to falls with three drains and a dozen penetrations is a lot of folded corners for a sheet product. The trade-off is the take-off. A liquid membrane is bought against a dry film thickness on the technical data sheet, not against floor area alone, and the wet volume depends on the product's solids content — the fraction that stays behind once the water or solvent has gone. Order by area and a nominal coverage figure and you are a drum short at the coving.

Above the membrane comes the bed, and this is where kitchen practice parts company with a domestic floor. Quarry tile in this duty is set in a thicker, fully bedded mortar rather than a combed thin-bed layer, because the enemy here is thermal shock and voids: a floor sitting at eighteen degrees hit with washdown water at eighty expands hard against everything restraining it, and any void under a tile becomes a pocket that fills with water and grease and then generates pressure the next time it is steam cleaned. Full contact under every tile is not a warranty target on this job, it is the mechanism. The methods for this construction sit in the ANSI A108 series, with A108.1A covering installation in the wet-set method with portland cement mortar, in the wet-area and food-service methods of the TCNA Handbook, and in BS 5385-4, the code of practice for ceramic and mosaic tiling in special conditions, which is the British document written for exactly this exposure.

Quarry Tile Is Not Porcelain With a Rough Face

Quarry tile is unglazed extruded tile made from natural clay or shale — that is the description ANSI A137.1 works from, and BS EN 14411 classifies extruded tile by water absorption in the same family. Two consequences follow for a tiler. It is thick, commonly twelve and a half to twenty millimetres and more in heavy-duty ranges, which changes the bed, the joint depth and the height of every trim you buy. And its colour goes the whole way through, so a chipped arris on a quarry tile reads as wear rather than as damage, which is a large part of why the material has survived in kitchens while prettier products have not.

Slip resistance is the specification line most often quoted and least often understood. ANSI A326.3 is the current test method for dynamic coefficient of friction on hard surface flooring, and 0.42 wet is the value it names for level interior surfaces expected to be walked on when wet. Two honest caveats belong next to that number every time it is used: the standard itself is explicit that meeting it does not guarantee nobody will slip, and a laboratory wet test with water is not a kitchen floor carrying rendered fat, which is a different lubricant behaving differently. The older static coefficient method, ASTM C1028, has been withdrawn — a data sheet still quoting a static figure is quoting a test that no longer stands. Where the exposure is genuinely greasy, the profiled and abrasive-grain quarry finishes exist for good reason, with their own trade-off: a surface rough enough to grip through fat is a surface that holds fat, and it wants a deck brush rather than a mop.

Then the module, which is where the take-off starts. A 194 by 194 millimetre tile at a ten millimetre joint gives a 204 millimetre module; our forty-eight square metres divided by 0.204 squared is 1,153 tiles before a single cut. Waste on a kitchen is not the five to ten per cent of a straight domestic lay — the cuts around two gullies, a channel run, the equipment plinths and the whole coved perimeter push it to ten per cent and beyond, and the offcuts from a twenty millimetre extruded tile are not reusable the way porcelain offcuts are. Order the cove pieces, the internal and external corners and the capping from the same batch at the same time; they are the slow-moving items in a quarry range and a second delivery three weeks later will not match.

The Joint Is Where the Money and the Risk Both Sit

Cement grout fails in a kitchen for two chemical reasons and one thermal one. Animal fat saponifies against an alkaline cement matrix; the lactic, acetic and citric acids that come off food waste attack portland cement directly; and hot washdown water accelerates both while cycling the joint through a temperature range the material was never asked about. The result is not dramatic — a joint that goes soft, then powdery, then hollow, then a route into the bed. Grouts are classified in ISO 13007 with a cementitious designation and a reaction-resin one; in the ANSI system the chemical-resistant water-cleanable epoxies are specified to ANSI A118.3 and the furan resin mortars and grouts to ANSI A118.5.

Epoxy covers most commercial kitchen duty and is water-cleanable inside its working time, which is what makes it a tiler's material rather than a specialist's. Furan belongs where the exposure is genuinely aggressive — strong acids, sustained high temperature, some brewery and food process floors — and it is not something to learn on a live job. Furan work is normally a trained applicator's scope, the tile faces are protected before grouting so the resin can be cleaned back off them, and the handling requirements are in a different class from anything in a domestic tiler's van.

Pot life is the thing that reorganises your day. A cement grout can be mixed by feel and worked until it stiffens. A two-part epoxy is a fixed ratio in a kit, with a pot life on the data sheet that is usually well under an hour and gets shorter as the room warms — and by the time you are grouting, the equipment is often back in and the room is no longer the cool empty shell it was on day one. You mix whole kits, never a part kit judged by eye, and you mix only as many as the crew standing in the room can place, pack and wash off before the material goes. That constraint sets your crew size for grouting day rather than the other way round, and it is the single most common reason a kitchen floor gets grouted badly by people who tiled it well.

The quantity comes off the module, not off a tape. Two divided by the module in metres gives the joint length in a square metre: at a 204 millimetre module that is 9.8 metres per square metre, so forty-eight square metres carries about 470 metres of joint. At ten millimetres wide and filled to the full twenty millimetre depth of the tile, 470 by 0.010 by 0.020 is 0.094 cubic metres — ninety-four litres, close to two litres for every square metre of floor. The same room in 600 by 600 porcelain with three millimetre joints would take about five litres in total. That factor of twenty is the number to have in your head before anyone asks you for a price.

One refinement, and it runs in your favour. Multiplying total joint length by width counts every crossing twice, because the intersections belong to both directions — one square of joint width per tile, ten by ten millimetres at twenty deep, which across 1,153 tiles is 2.3 litres. The true void is 91.8 rather than 94.1. Leave the over-count in place: it is a two-and-a-half per cent margin sitting exactly where you want one, given that epoxy is bought in whole kits and there is always a joint deeper than the drawing believed. What does need correcting is the depth itself. Twenty millimetres assumes the joints are raked out clean to the underside of the tile; a bed that has squeezed halfway up the joint gives a different figure and a shallower, weaker seal. Rake, brush, and check the depth with a piece of the tile before you mix anything.

Every Edge That Stops Has to Be Finished

In a kitchen an exposed tile arris is a hygiene defect before it is a chipping risk: a raw cut edge on an extruded tile is porous, it collects, and it is exactly the sort of detail an inspector runs a finger along. So the edges get counted as their own line, and there are more of them than a domestic floor has. The top of the coved skirting all the way round. Every threshold where the quarry stops and something else starts. The kerb at the pot wash and the step into the walk-in. The vertical and top edges of each equipment plinth. And the margin where the tile meets a channel drain frame, which is the one people leave until they are already short.

There are two ways to finish an edge and they have different take-offs. A quarry range normally includes coved skirting with a rounded top, plus internal and external corner pieces and a capping section; where you use those, the edge is solved in fired clay and the trim schedule does not count that run. Where a field tile is turned up the wall instead, the top edge is a cut edge and takes a metal profile. Choose the route before you count, because switching halfway leaves either a stack of corner pieces nobody needs or a shortfall on the longest run in the room.

Two things govern which profile you buy. Height is set by the tile plus its bed, not by the tile — and on a thick-bedded quarry floor that bed is not the two or three millimetres you allow over a thin-bed job. Size it off the bare tile thickness and the profile sits low, leaving a lip that catches a mop and holds water; guess high and it stands proud for a trolley wheel to find. Material is the other. Caustic degreasers and standing chlorides attack aluminium, so in a kitchen the profile and its fixings are stainless or they are a maintenance item with a date on them.

For our eight by six room the count runs like this: twenty-eight metres of perimeter less 3.4 metres of openings gives 24.6 metres of cove top, plus 3.4 metres of threshold, plus two plinths at roughly four metres of exposed edge each, plus 3.2 metres of kerb at the pot wash — thirty-nine metres before any allowance. Eight per cent for mitres and offcuts takes it past forty-two metres, and that is what the supplier needs alongside the height and the finish. One last check before you send it: trim comes in fixed stick lengths, so forty-two metres in two-and-a-half metre sticks is seventeen sticks, and any run you want unjointed has to fit inside a single one or be ordered long.

1. Walk the room and mark every edge that will be exposed, including the plinths and the drain margins, before pricing anything.
2. Decide edge by edge whether it is finished in a shaped quarry piece or a metal profile, and count only the profile edges.
3. Fix the profile height from the tile thickness plus the actual bed thickness, taken from the build-up you settled at the membrane.
4. Specify stainless for both the profile and its fixings wherever degreasers or chlorides will reach it.
5. Convert the run into whole sticks, checking that any length you want unjointed fits inside one.