Grout fills the joints between tiles, and while it is often an afterthought in tile project planning, it has a big impact on the finished appearance, durability, and maintenance of the installation. The wrong grout type can crack or stain; the wrong color can make beautiful tile look amateurish. Here is what you need to know about the main grout types, how to estimate quantities, and how to mix and apply it correctly.
The most fundamental grout decision is whether to use sanded or unsanded grout. The choice is dictated almost entirely by the width of your tile joints.
Sanded grout contains fine sand particles that add body and prevent shrinkage. Use it for any joint wider than 1/8 inch. It is the standard choice for floor tiles with 3/16-inch or larger joints and for most outdoor applications. The sand particles can scratch polished or soft stone tiles like marble if you are not careful during application and cleanup. Test in an inconspicuous area first or use a non-scratch sanded grout formulated for natural stone.
Unsanded grout has a smooth, paste-like consistency and is used for joints up to 1/8 inch wide. It is the right choice for wall tiles with tight grout lines, glass tile, and polished stone where the sand in sanded grout would cause scratching. Unsanded grout shrinks more than sanded grout as it cures, which is why it is not suitable for wider joints. It will crack.
Epoxy grout is a two- or three-part system consisting of a resin and a hardener that are mixed together just before use. Once cured, epoxy grout is nearly impervious to stains, moisture, and chemicals, making it the premium choice for kitchen backsplashes, commercial kitchens, and any area exposed to grease or harsh cleaning agents. It does not require sealing. The trade-offs are cost (typically three to five times the price of cement-based grout), a shorter working time once mixed, and a more demanding application process that requires careful temperature management. Epoxy grout is increasingly available in pre-mixed single-component versions that are more forgiving for DIYers.
Grout coverage depends on four variables: tile size, tile thickness, joint width, and the grout product's specific yield. Manufacturers print a coverage chart on the bag that accounts for these variables. As a general starting point, a 10-pound bag of sanded grout covers approximately 40 to 60 square feet of 12x12 tile with a 3/16-inch joint. The same bag covers only 15 to 25 square feet of 2x2 mosaic tile with the same joint width, because the smaller tiles have far more linear feet of joint per square foot of area.
For a manual estimate, the grout weight per square foot equals: (tile length + joint width) x (tile width + joint width) x tile thickness x joint width x grout density, divided by (tile length x tile width). This looks complex, but the manufacturer's chart gives you this result directly. Input your tile size and joint width and read the coverage in square feet per pound. Multiply your total square footage by the pounds-per-square-foot figure and divide by the bag weight to find the number of bags needed. Always buy one extra bag.
Pre-mixed grout (sold in buckets) is convenient for small jobs but is limited to unsanded formulations and can be slow to set. For most floor and wall tile jobs, you will mix dry grout powder with water. Add the powder to the water, not water to powder, to control the consistency. The target is a peanut-butter-like consistency that holds its shape without being stiff or crumbly. Mix thoroughly with a margin trowel or a low-speed drill with a paddle attachment. Let the mixture rest (slake) for 5 to 10 minutes after the initial mix, then stir again before use. This rest period allows the polymers in the grout to fully hydrate. Do not add water after slaking. It weakens the final product.
Most cement-based grouts have a working time of 20 to 30 minutes once mixed, less in warm weather or direct sunlight. Mix only as much as you can use in that window. In temperatures below 50 degrees F, grout cures slowly and may not reach full strength. Most manufacturers specify a minimum application temperature of 50 degrees F. In hot weather, work in small batches and keep the grout out of direct sun.
Hold the rubber float at a 45-degree angle and spread grout diagonally across the tile joints, pressing it firmly into the joints as you work. Work in small sections of 10 to 15 square feet at a time. Once the joints are packed, hold the float at a steeper angle (about 80 degrees) and sweep diagonally to scrape off excess. Wait until the grout has set enough to resist your fingerprint, typically 15 to 30 minutes, then clean the tile surface with a lightly dampened sponge in a circular motion. Wring the sponge out thoroughly between passes; excess water dilutes the grout and weakens it. After the haze dries (30 to 60 minutes), buff the tiles with a dry cloth.
Cement-based grout is porous and will stain if left unsealed in kitchens, bathrooms, or entryways. Apply a penetrating grout sealer after the grout has cured fully. Most products call for 48 to 72 hours of cure time before sealing. Apply the sealer along the grout lines with a small brush or roller applicator, let it penetrate for the time specified on the product label, then wipe off the excess. Reapply sealer annually in heavy-use areas and every two to three years in lower-traffic rooms. Epoxy grout does not require sealing. Dark grout colors are more forgiving on stains in kitchens and mudrooms; white or light grout in a high-traffic floor requires diligent sealing and cleaning to stay looking fresh.
