Tile Kitchen Floors: Porcelain vs. Ceramic, Slip Resistance and Size

A tile floor is the most durable surface you can put in a kitchen, and the least forgiving of a poor choice or a poor installation. The tile itself rarely fails. What fails is a slippery finish chosen for its looks, a floor that flexes under rigid tile, or large tiles laid over a surface that was never flat. This page covers the tile, the ratings on its spec sheet, and the layers beneath it.

Porcelain versus ceramic

Both are fired clay. The dividing line is density, measured as water absorption. The Tile Council of North America (TCNA) states that porcelain tile has water absorption of 0.5 percent or less under the ASTM C373 test, and that non-porcelain tile absorbs more than 0.5 percent. TCNA also notes that many products sold as porcelain do not meet that definition, and that tile carrying the Porcelain Tile Certification Agency (PTCA) mark has been certified as true porcelain.

For a kitchen floor, porcelain is the default, mainly for chip resistance. On a wall the balance is different, as explained in backsplash tile materials compared.

Wear ratings

Glazed tile is tested for how soon abrasion becomes visible, under ASTM C1027, and sorted into classes from 0 to 5. Showrooms often call this the PEI rating. TCNA points out that the correct reference is the test method, and says a class of 3 is common for most interior residential areas and 4 for most commercial spaces. A kitchen is a hard-working residential room, so look for class 3 or higher and treat the maker's "suitable for residential floors" statement as the deciding line.

Unglazed porcelain has no glaze to wear through and is tested differently. On glazed tile, lighter, matte and speckled surfaces hide the gradual dulling of a traffic path far better than dark, glossy, solid colors.

Slip resistance and DCOF

Slip resistance on hard flooring is measured as the dynamic coefficient of friction (DCOF) under ANSI A326.3. The 2021 edition sorts products into five use classifications:

A home kitchen floor gets wet, so the classification to look for on the spec sheet is Interior, Wet. A tile classed only as Interior, Dry is meant for floors that are kept dry when walked on.

Read the number with the caution the standard itself gives. TCNA quotes ANSI A326.3 as saying the measured DCOF "shall not be the only factor in determining the appropriateness" of a flooring material, because footwear, contaminants, slope and maintenance all affect the risk of a slip. A kitchen adds cooking oil, which is more slippery than water. In practice:

• Choose matte, honed or lightly textured surfaces over polished ones.
• Smaller tiles add grout lines, and grout lines add grip.

Tile size and flatness

Large tiles mean fewer joints and a calmer floor. They also raise the standard of everything beneath them. Two tiles meeting at slightly different heights is called lippage, and a large tile cannot follow a dip the way small tiles can.

A TCNA technical article on large-format tile notes that the industry handbook's general limit is a 1/4 inch maximum deviation from flat in 10 feet, and advises stricter tolerances for large tile, especially with narrow joints. Getting there usually means patching or a self-leveling underlayment before any tile is set. The same article makes two points worth knowing when you choose a layout:

• Tiles are not perfectly flat. Long tiles tend to have a slight bow. A brick pattern that puts the middle of one tile beside the ends of its neighbors sets the high point against the low points. Ask your installer what offset the tile maker allows; many limit how far long tiles may be staggered.
• Light exposes everything. Low sun through a patio door, or lighting that washes across the floor, makes small height differences visible. A slightly wider joint softens them.

Grout joints on a floor

Floor joints are a little wider than wall joints as a rule, because floor tile varies more and the joint has to absorb it. The joint width follows from the tile: rectified tile can take a narrow joint, and standard pressed tile needs more. On a kitchen floor, pick a mid-tone color and a stain-resistant grout, since this is the grout that sees dropped food and mop water. Types, sanded versus unsanded and color are all in the grout guide.

The edges of a tile floor are not grouted tight to the walls and cabinets. TCNA recommends allowing for expansion and contraction in every tile installation. In a small room a gap at the perimeter, hidden by the baseboard, is sufficient, and larger or sunlit floors need movement joints within the field, filled with flexible sealant.

What goes under the tile

Tile and grout are rigid. They crack when the surface beneath them bends or shifts, so the layers below are where a tile floor is won or lost.

Over a wood-framed floor

The framing and subfloor must be stiff enough for tile, and stiffer still for natural stone. In older houses that can mean adding blocking, sistering joists or adding a layer of plywood. The stiffness limits come from the building code and the tile industry handbook, and the installer should be able to say which recognized installation method is being followed. On top of the subfloor goes one of:

• Cement backer board, bedded in mortar and screwed down. A stable, familiar base that adds height.
• An uncoupling membrane, a thin sheet that lets the tile layer and the subfloor move slightly independently. It adds little height, which helps at doorways.
• A mortar bed, the traditional method, thick and very flat, used where the floor needs significant correction.

Over a concrete slab

Tile can bond directly to a sound, clean slab. Slabs crack, and a crack will travel up through tile bonded over it. A crack isolation membrane, a product category with its own standard (ANSI A118.12), is applied over hairline cracks so they do not print through. It is not a fix for a slab that is still moving or for structural joints, which must be carried up through the tile as movement joints.

Height

Underlayment, mortar and tile together are usually thicker than the floor they replace. That affects the dishwasher opening, the toe kick height and every doorway. It is resolved on paper, with the cabinet plan, as described in the overview of kitchen flooring options. Removing the old floor to regain height brings in the check described in asbestos and kitchen remodels in Clark County.

Comfort and warmth

Tile is hard and, unheated, cold. For the cold, tile is the floor that pairs most naturally with electric floor warming, because it conducts heat well and is not harmed by it. The mat goes in before the tile, so the decision cannot wait. See heated kitchen floors.

What to check before you buy

• Porcelain or ceramic, and for porcelain whether it carries the PTCA certification mark.
• That the maker rates it for residential floors.
• The ANSI A326.3 use classification: Interior, Wet for a kitchen.
• Visible abrasion class for glazed tile.
• Rectified or not, and the minimum joint the maker recommends.
• The maximum offset the maker allows for a staggered pattern.
• Shade and caliber marked the same on every box.
• The installation method your tile setter will follow, and what flattening the floor needs first.

Who should choose which

• A hard-use family kitchen: matte porcelain in a mid tone, medium to large format, stain-resistant grout.
• A kitchen with an exterior door: textured porcelain with an Interior, Wet classification.
• An older house with a floor that is not flat: smaller tile, which follows the floor more gracefully, or budget for flattening before large tile.
• You want a wood look with no water worry: porcelain plank, on a very flat floor, with the stagger the maker allows.
• You stand and cook for hours, or the framing is light: compare the alternatives in hardwood versus LVP versus tile before committing.

JDI Construction checks the floor structure during design and puts the underlayment, tile layout and joint width in the plan. To discuss a tile floor as part of a kitchen project, see our Vancouver kitchen remodeling page.