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Applying Grout To ensure strong joints, the grout must fill the joints completely at a uniform density. Packing grout with a rubber trowel forces the solid particles to crowd together, which pushes excess moisture out of the joint. To do this, hold the grout trowel at a low angle to the face of the tile and press the grout into the joint from several different directions (Figure 6).

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Figure 6. Force the grout into joints by holding the rubber trowel at a shallow angle as you sweep it over the tile from several directions (top). To scrape away the excess, hold the trowel on edge and stroke the surface on a diagonal to the joint direction (bottom).

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Backfill any voids immediately. The grout should be forced into all joints — not just pushed around the surface. As one area is filled, hold the face of the trowel at a 90-degree angle to the surface of the tile (with the edge diagonal to the direction of the joints) and scrape away as much of the excess as possible. Job-site conditions will determine how much grout can be spread before wet cleaning can begin. With impervious tiles and mild temperatures, it may be possible to spread hundreds of square feet; with porous tiles and high temperatures, start off with a small area. As a matter of common sense, schedule grout work so that there is absolutely no traffic on freshly grouted surfaces.

Expansion Joints

Not all joints should be filled with grout. Some joints serve as expansion joints, and they are filled with caulk or sealant so they can absorb normal, expected movement generated by all residential or light commercial structures. Expansion joints do not stop the movement; instead they allow movement to occur without causing damage to the tile work. Complete information on the minimum width, placement, and frequency of expansion joints can be found in Handbook for Ceramic Tile Installation (Method EJ-171), revised and published annually by the Tile Council of America (100 Clemson Research Blvd., Anderson, SC 29625; 864/646-8453). While grouting, it is virtually impossible to keep grout out of expansion joints. In fact, to maintain the maximum density in the grouted joints, an installer must get some grout in the expansion joints so that the grout in neighboring joints has something to push against. Once the fresh grout has been thoroughly cleaned and has taken its initial set, however, it can be easily sliced out of the expansion joints with a dull knife blade or the tip of a trowel (Figure 7).

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Figure 7. After the grout has begun to harden, use a dull knife or the tip of a trowel to slice it out of expansion joints, which will later be filled with caulk.

Remove any stray crumbs with a vacuum, then apply caulk or sealant to the expansion joints after the grout has reached an acceptable cure. This is usually within 72 hours, but you should consult with the caulk or sealant manufacturer. There is no harm in caulking after the grout has fully cured, but if you caulk too soon, you may create a chemical reaction that can stain the grout or the sealant.