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Grout Joints

When it comes to stone and tiles for walls or flooring, a proper grout joint is an important part of the specification. While many architects and designers like the idea of a thinner grout joint for aesthetic and maintenance purposes, it's important to understand why a thicker grout joint may be better.
BENEFITS OF A PROPER GROUT JOINT:
1.) Reduce the likelihood that tiles will chip if/when the subfloor moves.
2.) Minimize the appearance of inconsistencies in tile.
3.) Minimize the likelihood that the tile pattern will be thrown off upon installation.
There is no standard for grout joints. According to the TCNA, the grout width can vary depending upon the size of the tile. Many stone and tile manufacturers suggest that grout joints be no less than 1/8" to 3/16".
WHY 1/8" OR MORE?
While the intent of a thinner grout joint is often to obtain a more desirable aesthetic, inconsistencies in the grout or tile are generally more evident in an installation with a thinner grout joint, which can give the installation a sloppy appearance. 
THINGS TO TAKE INTO CONSIDERATION WHEN CHOOSING THE THICKNESS OF GROUT JOINTS:
Tile Size
Large format tiles tend to create more lippage, or unevenness in the surface. Therefore, a thicker grout joint may be necessary.
LARGE TILES vs. SMALL TILES
Tile Variation (Differences in Size)
Grout joints must accommodate differences in thickness and tile size. Standards for tile manufacture allow for size variation from one tile to the next - often up to 3/32" difference between the largest tile and the smallest tile in the box. Therefore, grout joints need to be thick enough to accommodate this variation.
12"x24" NOMINAL TILES WITH SLIGHT VARIATION IN SIZE
Tile Variation (Differences in Shape)
There is less variation in rectified tiles, which produce the same size tile. Non-rectified, hand-crafted or artisanal tiles, on the other hand, have variation in shape from tile to tile, and also within the same tile. A thicker grout joint will accommodate these irregular edges.
RECTIFIED EDGES vs. NON-RECTIFIED EDGES
The Plane or Surface
Grout accommodates differences in the angle of the surface. As the plane of the tile changes (i.e. where the floor or wall is not level) the grout will slope from one tile to another. When tiling over a bump, the grout joint opens up; and when tiling across a depression, the top of the grout joint narrows. Although a proper grout joint accommodates subtle changes, surface leveling is necessary, particularly when installed using a thin-set method.
Aesthetic Consistency
When tiles are set too close together or have a grout joint that's too thin, any variance in that grout joint may be visible. This is especially noticeable on a thinner grout joint.A note about perimeter and field movement joints (soft joints): Grout variation differences are especially noticeable with soft joints, which occur every 20'-25' for interior and 8'-12' for exterior applications. These joints allow for expansion and contraction and must be a minimum of 3/8"-1/4" depending upon the tile type and the application. When compared to a 1/16" grout joint, this difference is highly visible.
Client's Preference
Once the client understands the benefits of a proper grout joint and the possible effects of a thinner grout joint, it's up to them to make a decision.

A NOTE ABOUT APPLICATIONS WITH THIN GROUT JOINTS
Many installations appear to have a grout joint of less than 1/8" or a butt-joint. In order to achieve this with stone, the installer must be extremely skilled, the surface must be level and - in many cases, the stone must be installed and then ground down to minimize differences. Many project budgets do not accommodate this luxury. In addition, perimeter and field movement / soft joints are highly visible in these applications. When your sub-floor moves, your tile has no where to go. Certain techniques, such as using anti-fracture membranes or expansion joints can alleviate some of the problems associated with thin grout joints or butt-joints, however these will not eliminate the problems altogether.
(*) Source: TCNA (Tile Council of North America). http://www.tcnatile.com/

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