When DIYers install tile they imagine it’s all about making the tile flat and level. You spend days fussing with the mortar bed and lippage; meanwhile, what happens between tiles is an afterthought.
Wrong. As soon as you take a peek down at your feet you’ll see the error of your ways. Your grout lines determines the overall look of wall or floor, its style. And if those grout lines are too wide, you won’t be able to hold anything on them without risk of breaking something or falling through. It is a structural choice pretending to be an aesthetic one.
Why Grout Lines Matter
This table matches certain width tiles to appropriate joint widths (above). And yes, you might assume that all the time, the smaller the better. That’s a mistake I see people make time and again, and it costs them money.
Sixteenth inch hairline joints on a shower wall is noticeable to the eye. On the floor they’re all but unattainable because of how that floor move with house. Substrate flexes, temperatures change; if you don’t provide sufficient space for your tile to breathe, the tile crack. A little extra space between each piece pays very little visually. A crack in a ceramic product is devastating structurally.
But also remember. It’s not just where, but what. Porcelain, when rectified (meaning, machine-cut to precise edges) can accommodates really thin grout lines (because they’re so straight). Natural stone vary in thickness and won’t have perfect edges. Handmade tile has its own warpage.
For example, if you attempt to lay rustic, handmade tile with a hairline joint, those gaps will be inconsistent and jarring. That visual chaos will detract from space. Wide joints hide such irregularities. They frame them to make their irregularity appear deliberate, not like a mistake in the installation. It’s all about setting expectations based off spacing.
That same width also determines type of grout you must use: Grout must be either unsanded (for joints less than one-eighth inch) or sanded (for joints wider than an eighth). Why? Think about how this all works.
Sanded grout has body and strength because it includes tiny particles of silica. But these particles are too large to fit through the narrowest spaces. Force sanded grout into a narrow joint and you’ll end up with a crumbly layer that won’t stand up to any pressure at all.
On the other hand, trying to fill wide joints with unsanded grout cause them to shrink, resulting in cracks. The mix isn’t reinforced from inside to span the distance. One-eighth inch seems to be the dividing line; below that, you’re cool with smooth, unsanded types; above that, sanded is your style. And no, it isn’t suggested, this one’s a hard-and-fast rule.
Also, large joints requires different installation techniques. It’s difficult to pack a wide joint well with a rubber float; it require some skill and time. Voids become places where water will collect and bacteria can grow.
Wide joints mean you will purchase more grout. Your bags of grout covers much less area if your lines are half-inch thick rather than narrow. That adds up on the budget in ways you don’t often consider before the job begins. You’re purchasing material that does nothing to support the structure except create space. However, you still need to purchase enough, mix it right, and seal it effectively.
It’s often a matter of balancing what looks good visually versus what makes practical sense. On one hand, you desire the seamless appearance of minimal joints. However, you live in a home with a wood subfloor that flexes slightly. Usually the compromise is to go with a moderate joint width, perhaps three-sixteenths of an inch. From a normal view, it still looks clean. And it has some flexibility so it won’t crack. Perfection isn’t the goal, it’s about durability. You should of wanted more than just looks.
The bottom line is that your whole install is bound together by grout lines. That’s where all the give comes from, where the rigid tile can’t manage any more. The key is getting that width so the tile stays beautiful for as long as the structure underneath it lasts. Use the right spacer, work within the limits of your materials, and make sure the joints line up correctly.
