Best Grout for Porcelain Tile: Types, Joint Widths and Pitfalls

For most porcelain tile, a high-performance polymer-modified cement grout (ANSI A118.7) is the best all-round choice: it fills 1/16 inch rectified joints, resists shrinkage and holds color. Use epoxy or urethane in showers and kitchens where staining matters, and test any grout on polished or unglazed porcelain first, since pigment can lodge in the surface.

Why porcelain changes the grouting rules

ANSI A137.1 defines porcelain tile as tile with water absorption of 0.5 percent or less. That density is the whole reason porcelain is durable, frost resistant and stain resistant. It is also the reason grout behaves differently against it.

When you grout absorbent ceramic wall tile, the tile edges draw some water out of the grout. The grout stiffens quickly, the surface firms up for washing, and the cement near the joint walls hydrates with a lower water ratio. Porcelain does none of that. The water stays in the joint, so:

• Grout takes longer to become firm enough to wash. Wipe too early and you drag cement out of the joints, leaving them low and sandy.
• Excess water rises to the surface. It carries fine cement and pigment with it, which is one cause of light-colored blotches (shading) and of efflorescence.
• Haze bonds tightly to dense surfaces. There are no pores for it to soak into, but the film it leaves is continuous and hard once cured.
• Cure times on the data sheet are minimums. In cool, humid rooms over porcelain, setters routinely see grout reach walkable firmness later than the TDS figure.

The fix is technique more than product: mix at the low end of the water range, let the grout set up in the joint until a thumb press barely marks it, then wash with a well-wrung sponge. The mixing guide covers water ratios and slaking.

Which grout for which porcelain

"Porcelain" covers several very different surfaces. Matching grout to the finish matters more than matching it to the word on the box.

The polished porcelain problem

Polishing grinds off the top skin of an unglazed porcelain body. That exposes closed pores that were sealed inside the tile, and on some products those pores are big enough to catch fine pigment particles. A dark or strongly colored grout on light polished porcelain can leave a gray shadow along the edges that does not wash off. Many polished porcelains leave the factory with a protective treatment; others recommend sealing before grouting.

The test is easy: grout a joint between two spare tiles with the exact grout and color, clean it as you would on the job, let it cure, and inspect under raking light. If the tile darkens or the haze will not come off, either apply the sealer or grout release the tile maker approves, or move to a grout color closer to the tile.

Cement, epoxy or urethane on porcelain

High-performance cement grout

High-performance cement grouts (ANSI A118.7, or ISO 13007-3 CG2WA where marked) are the default for porcelain floors and walls. Their polymer content improves bond to dense tile edges, which plain cement grout bonds to less well, and their shrinkage limits matter in narrow rectified joints. Many cover 1/16 to 1/2 inch in one formula, which suits mixed layouts. Color consistency is also better than with standard A118.6 grouts, which helps on porcelain because the tile itself rarely varies, so any grout shading stands out.

Epoxy grout

Epoxy (ANSI A118.3) is the strongest choice for shower floors, kitchens and commercial floors over porcelain: nearly impervious, stain resistant and unaffected by most cleaners. Porcelain is actually one of the easier surfaces to use epoxy on, because the dense face releases epoxy residue well when cleaned on time. The usual cautions apply: work in small areas, clean before the resin skins, and avoid it on textured porcelain unless you have practiced, because epoxy residue in surface texture is hard to remove. See how to apply epoxy grout.

Urethane and premixed grouts

Urethane and other single-component premixed grouts are popular on porcelain plank floors because they are ready to use, flexible and color consistent. Their weak point on porcelain is the same as cement's: they cure by losing water or reacting with air moisture, and the dense tile slows that. Respect the full cure time before wet use, and do not apply them in deep, wide joints beyond the TDS limits.

Large-format porcelain and grout cracking

Most "grout problems" on large porcelain are installation problems that surface at the grout line. A 24x48 tile is stiff and hard to bed fully; if it rocks or the floor flexes, the joint is where the movement shows. Before blaming the grout, check for these causes:

• Coverage. ANSI A108.5 calls for average mortar contact of at least 80 percent in dry interior areas and 95 percent in wet areas and exteriors, and large-format installers generally aim for full support at edges and corners. Hollow corners flex and crack the adjacent grout.
• Substrate flatness. For tile with any edge over 15 inches, ANSI A108.02 calls for no more than 1/8 inch deviation in 10 feet and 1/16 inch in 24 inches.
• Movement joints. Large porcelain fields need sealant joints at perimeters and in the field per TCNA EJ171. Without them, stress relieves itself as cracked grout or tented tile. See caulk vs grout.
• Offset. With planks and large tile, keep running-bond offsets at 33 percent or less unless the maker approves more; centered (50 percent) offsets put the high point of one bowed tile against the low ends of its neighbors.

For diagnosis of existing cracks, see why grout cracks.

Haze and cleanup on porcelain

Porcelain's density makes haze both easier and harder. Easier, because it cannot soak in; harder, because a cement film on glass-smooth porcelain shows every streak. A few practices help:

1. Wash late, not early. Wait until the grout is firm in the joint. Early washing on porcelain pulls grout and leaves more cement on the face.
2. Use two buckets. One for rinsing the sponge, one clean. Dirty rinse water redeposits cement.
3. Buff the light film. Once the surface dries to a haze, buff with a dry microfiber or cheesecloth before it hardens.
4. Treat cured haze with the right cleaner. On porcelain, a buffered acidic haze remover is usually safe after the grout has cured per the TDS, but test first on polished finishes and never use acid near stone trim. Epoxy haze needs an epoxy-specific remover.

The full process is in how to remove grout haze.

Color and sealing decisions

Because porcelain itself is uniform and rarely needs sealing, the grout is usually the only part of the floor that stains or changes color. That pushes the decision in two directions: pick a mid-tone grout that hides wear (pure white and near-black both show soil and residue), or pick a grout that does not need sealing at all, such as epoxy. Cement grouts on porcelain floors are commonly sealed with a penetrating sealer once cured; see do you need to seal grout. For color strategy, the grout color guide and color visualizer help.