Standard grout is made of Portland cement, water, and sometimes sand. That simple mixture accounts for the vast majority of grout used in homes, but specialty grouts swap cement for epoxy resin or other materials to handle tougher conditions. The exact ingredients determine how the grout performs, how long it lasts, and where it should be used.
Cement Grout: The Most Common Type
The grout between most bathroom and kitchen tiles is cementitious grout. Its base ingredient is Portland cement, a powder manufactured by crushing and heating limestone, sand, clay, and iron ore at extremely high temperatures. The calcium, silica, and alumina in those raw materials fuse into a substance called clinite, which is then ground into a fine powder. A small amount of gypsum is added to control how quickly the cement sets. When you mix this powder with water, a chemical reaction hardens it into a rigid solid.
Beyond cement and water, most cementitious grouts contain some combination of fillers, pigments, and polymer additives. The fillers are typically fine sand or limestone powder. Pigments are almost always synthetic iron oxides, the same family of mineral colorants used to tint concrete blocks and bricks. Iron oxides produce the full spectrum of grout colors you see on store shelves: yellows, reds, browns, blacks, and everything blended in between. White grout simply skips the pigment or uses titanium dioxide.
Many modern cement grouts also include a polymer additive, often a type of acrylic latex. These polymers fill microscopic pores in the cured grout, making it more water-resistant, more flexible, and less likely to crack. Some products come with the polymer already blended into the dry mix. Others require you to substitute a liquid latex additive for some or all of the mixing water.
Sanded vs. Unsanded Grout
The difference between sanded and unsanded grout is exactly what it sounds like: one has sand mixed in and the other doesn’t. According to the Tile Council of North America, joints 1/8 inch and wider should be filled with sanded grout, while joints narrower than 1/8 inch call for unsanded grout. The sand particles act as a structural filler. Without them, thicker grout lines shrink and crack as they cure because there isn’t enough solid material to hold the shape.
For joints wider than 3/8 inch, you need an even coarser mix. Some manufacturers sell a “wide joint” grout with heavier sand content, or you can add coarse sand to a standard sanded grout yourself. Unsanded grout, by contrast, is just cement, water, pigment, and fine powder fillers. Its smoother texture makes it easier to press into very thin joints and to work on polished stone surfaces that sand could scratch.
Epoxy Grout Ingredients
Epoxy grout contains no cement at all. It’s built around a two-part epoxy resin system: the resin itself and a chemical hardener. The resin is typically a type called bisphenol A epoxy, and the hardener is an amine compound that triggers the curing reaction when the two parts are combined. Once mixed, the resin cross-links into a hard, dense plastic.
To give epoxy grout the right consistency for tiling, manufacturers blend in a filler. Silica sand is the most common, usually making up two to three parts filler for every one part resin mixture. Other possible fillers include calcium carbonate and titanium dioxide (which also serves as a white pigment). The result is a grout that’s essentially plastic reinforced with sand, which is why epoxy grout resists water, stains, and chemicals far better than cement-based products. It won’t absorb coffee spills or grow mold the way porous cement grout can.
The tradeoff is cost and workability. Epoxy grout is significantly more expensive, sets up faster, and has a stickier texture that makes it harder to clean off tile surfaces during installation. It’s most common in commercial kitchens, hospitals, swimming pools, and other spaces where chemical resistance and hygiene matter more than ease of application.
Furan Grout for Industrial Use
Furan grout is a niche product you’re unlikely to encounter in a home. Its base is furfuryl alcohol, a resin derived from agricultural waste like corn cobs and sugarcane stalks. When this resin is exposed to an acid catalyst, it undergoes a hardening reaction that produces an extremely chemical-resistant solid. The cured grout stands up to strong acids, solvents, and high temperatures that would destroy both cement and epoxy grouts.
Furan grout is used in laboratories, chemical processing plants, and industrial facilities where floors and walls are regularly exposed to harsh substances. It’s typically black, has a strong odor during installation, and requires specialized handling. Carbon powder is a common filler.
What Makes Grout Different From Mortar
Grout and mortar share the same basic ingredients (cement, water, sand), but they’re formulated differently for different jobs. Mortar is the adhesive that bonds tiles or bricks to a surface. It’s mixed thicker, with a higher ratio of sand to cement, so it holds its shape under weight. Industry standards specify that mortar aggregate should be two and a quarter to three and a half times the volume of the cement.
Grout is designed to flow into joints, not bear structural loads. It uses more water relative to cement, giving it a thinner, more pourable consistency. Unsanded grout in particular is almost paste-like. This higher water content means grout is more porous once cured, which is why sealing cement grout is often recommended for wet areas. Epoxy grout sidesteps this problem entirely since its cured resin matrix doesn’t absorb water at all.
Polymer Additives and What They Do
If you’ve seen grout labeled “polymer-modified” or “latex-modified,” the additive is usually a polyacrylate or acrylic latex. These are tiny plastic particles suspended in liquid. As the grout cures, the polymer particles fill gaps between cement grains and form a flexible film throughout the material. Research on polyacrylate-modified cement materials shows that increasing the polymer content reduces porosity, improves strength, and significantly cuts down on water absorption.
In practical terms, polymer-modified grout is less likely to crack when your house shifts slightly with temperature changes, less prone to staining because it absorbs less liquid, and more resistant to crumbling over time. Most pre-mixed grout sold at hardware stores already contains these polymers. If you’re buying a dry powder mix without them, you can purchase a separate liquid latex additive to mix in instead of plain water.
Some grouts also include antimicrobial agents to slow mold and mildew growth. These are typically built into the formula by the manufacturer rather than added by the installer. They help, but they don’t eliminate the need for regular cleaning in wet environments like showers.