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Success with ceramic tile as a finishing material always depends on the materials that support and surround it. Grout is a key ingredient, because grout determines whether or not the finished joint will perform as expected. Ceramic tile grout is both practical and decorative. Cured grout protects the fragile edges of tile and supports compressive loading, which is especially important for floor tiles. Also, when grout is properly installed, the tile can be easily cleaned and maintained, which contributes to the overall appearance of the installation. Once cured, Portland cement-based grout is immune to damage by water (even when fully immersed, as it would be in a swimming pool or fountain). But contrary to popular opinion, grout is not a waterproofing material that can eliminate the passage of water or moisture. Many types of grout are available to suit different kinds of tile as well as various performance conditions ranging from dry, light-duty wall tile to wet locations with heavy floor traffic (see ","). In this article, however, I will be talking about Portland cement-based and latex grouts. Epoxy grout differs radically and is best left to another article.

Preparation

Before grouting, the tile joints must be cleaned of all adhesive residue to a depth equal to two-thirds the thickness of the tile. Ideally, excess adhesive should be removed while it is still soft. If the adhesive has hardened, use a narrow tuck-pointing trowel, a utility knife, or a scraper to pare down any excess (see Figure 1).

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Figure 1. Patches of excess adhesive buildup in the joints can cause splotches on the surface of colored grout. If the adhesive hardens before it can be removed, cut away any excess with a tuck-pointing trowel or scraper to a depth of two-thirds the tile thickness. This is particularly important when applying colored grouts, since variations in the joint depth can cause splotchy color at the surface. Temperature and humidity also affect grout. In hot climates, if supplemental cooling is not available, it may be necessary to apply the grout early in the day, before temperatures rise. At the other end of the thermometer, temperatures below 50°F will suspend hydration. In this case, you may need to provide supplemental heat till the grout has fully cured. Beware of unvented heaters. Carbon monoxide and other contaminants in the exhaust pose a health threat to tile workers, and may react with and degrade the grout as well. The types of tile and adhesive used also affect the grouting process. Non-vitreous tiles and regular adhesive mortars absorb moisture. For these applications, misting the tiles with a garden sprayer or washing the tiles with a damp sponge just before grouting can help improve the strength of the finished grout and speed up the grouting process. On the other hand, vitreous tiles and low-absorbing adhesives (like some cured mastics and latex or epoxy adhesives) do not require misting or sponging. When conditions call for misting or sponging, keep water from puddling in the joints. Even small droplets of excess water in the joints can weaken any grout and cause variations in the hue of colored grouts.

Tools.

Proper grouting demands at least one specialized tool — a rubber trowel that can compress grout into the joint without scratching or marring the face of the tiles (Figure 2).

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Figure 2. A rubber trowel is essential for grout work, because it forces grout into joints without marring the tile surface.

Margin and pointing trowels are useful for mixing, placing, or trimming fresh grout. Clean buckets are essential, as are soft cloths or towels for removing cement haze from the surface of the tiles. You’ll also need round-edged sponges, available at tile and masonry supply houses. A powerful shop vacuum is great for final cleaning, and don’t forget barricades to keep traffic off freshly grouted tile.