Grout lines for wood look tile: 1/8, 3/16 and what the standard says

Almost everyone shopping for plank tile asks for the thinnest grout line they can get, usually 1/16 inch, because they want the floor to read as boards rather than as tile. It is the right instinct and the wrong number.

Here is the short answer. On our tiles, 1/16 inch is not available at all. For a wood look plank laid in a running bond, plan on 3/16 inch, and the reason comes from the installation standard rather than from us.

Why 1/16 inch is off the table on a formed edge

Tile comes in two kinds of edge. A rectified tile is pressed as a large sheet and then sawn down to an exact size, which leaves a sharp, square, dimensionally precise edge. A calibrated tile, sometimes called non-rectified, is pressed to size in its own mold, so the edge comes out softly rounded and the sizes vary very slightly from piece to piece.

Every tile we make is calibrated with a formed curve edge. That is deliberate: a rounded edge is what makes the joint read as the shadow line between two boards instead of a grid drawn on the floor. Run a finger across a sample and you can feel which kind you are holding.

The cost of that choice is joint width. A 1/16 inch joint needs the dimensional precision of a sawn edge. On a formed edge it would leave nowhere for the slight size variation to go, and the rows would run out of line within a few courses.

What the standard actually asks for

This is not a house rule. ANSI A108.02 sets minimum average grout joint widths, and the Ceramic Tile Education Foundation sets them out plainly:

• For a running bond pattern where any side of the tile is 15 inches or longer, the average joint should be at least 1/8 inch on rectified tile.
• On calibrated, non-rectified tile the average joint should be at least 3/16 inch.
• The joint also has to grow by the amount of edge warpage on the tile's longest edge.

Every plank we make is longer than 15 inches. 150x900mm is 6 x 36 in, and the longest is 8 x 56 in. So the 3/16 inch figure is the one that applies to our tiles in a running bond.

One caveat worth raising with your installer: sources differ on whether the trigger length is 15 or 18 inches, depending on the edition being quoted. Our planks are well past both, so it does not change the answer here, but it is worth confirming against the current text if you are writing a specification.

How that lines up with our own figures

Our laying catalog calls for spacers of at least 3 mm and draws a 4 mm minimum joint on unrectified tile, and our blogs give a working range of 3 to 5 mm. In inches that range is roughly 1/8 to 3/16.

So the two sets of numbers agree, and 3/16 inch sits at the top of our range rather than outside it. If you want one figure to give an installer for a long plank in a running bond, 3/16 inch (about 4.8 mm) satisfies both the standard and our catalog.

The offset matters as much as the width

A thin joint is not the main cause of a floor that looks uneven. The offset is.

The standard limits running bond offset to 33 percent for tiles over the threshold length, and a greater offset needs a mock-up approved by the owner or specifier. The reason is lippage: a plank is very slightly bowed along its length, so the more you slide the next row along, the closer a high point sits to a low point. The International Masonry Institute explains how warpage turns into lippage on long tiles.

This is why our laying catalog specifies a quarter-plank offset and crosses out the 50:50 half offset:

• 225 mm on 150x900mm
• 300 mm on 200x1200mm
• 350 mm on 200x1400mm

A quarter offset is 25 percent, which is inside the 33 percent limit. The half offset that looks natural on a brick wall is 50 percent, which is outside it, and on a 56 inch plank it is the single fastest way to end up with lippage you can feel barefoot.

Picking a grout color, now that the width is settled

With a 3/16 inch joint, the color choice carries real weight because the line is visible.

Close to the plank is the safe choice and the one that makes the floor read as boards. The formed edge already gives you a shadow line, so you are not losing definition.

One shade darker than the plank works in a kitchen or an entry, where a pale joint shows traffic within a year.

Deliberate contrast turns the floor into a visible grid. That is a design decision rather than a mistake, but see it in a large sample before committing, not on a single tile.

Ask for a grout rated for the room, and have the haze cleaned off the same day. Grout haze is the most common complaint on a new floor and it is not a tile fault.

What to tell your installer

• Average joint 3/16 inch, with spacers of at least 3 mm.
• Quarter-plank offset, not 50:50.
• Flatten the subfloor first. The usual working tolerance is 1/8 inch over 10 feet, and long planks punish a dip.
• One calibre code per room, with the back arrows all running the same way.
• Dry lay the first few courses before anything is fixed.
• Order 10% extra and keep it, so a damaged plank years later is a swap.

Specifications for each format are in the downloadable catalogs.

The short version

Ask for 3/16 inch and a quarter-plank offset, and the floor will look like boards and stay flat. If a 1/16 inch joint is genuinely a requirement of your design, you need rectified tile and we are not the right supplier, which is better said now than after delivery. The wider trade-offs of plank tile are in the honest pros and cons, and grout in a wet area is covered in our shower guide.

Tell us the format and the square footage and we'll come back with a rate. Talk to our team.

Frequently asked questions

Can I use a 1/16 inch grout line with wood look tile?

Not with ours. A 1/16 inch joint needs a rectified, sawn edge, and every tile we make has a formed curve edge. The standard asks for at least 3/16 inch on calibrated tile in a running bond.

What grout line should I use for wood look plank tile?

3/16 inch as an average for a plank longer than 15 inches in a running bond. That satisfies ANSI A108.02 for calibrated tile and sits inside our own 3 to 5 mm range.

Why do long planks need a wider joint than square tiles?

Because a long plank has slight warpage along its length, and the joint absorbs that variation. The longer the tile, the more there is to absorb.

Does a wider grout line make the floor look less like wood?

Less than people expect. The formed curve edge reads as the shadow between two boards, so a joint grouted close to the plank color still looks like boards rather than tile.

What offset should the planks be laid at?

A quarter of the plank length, which is 25 percent. The standard caps running bond offset at 33 percent for long tiles, and the 50:50 half offset is both outside that and ruled out in our laying catalog.

What causes lippage in a plank tile floor?

An uneven subfloor and too much offset, in that order. Flatten the floor first, keep the offset to a quarter plank, and dry lay before fixing.