June 1, 2006
Movement joints are an essential part of every tile installation. On residential floor installations, movement joints should be located anywhere the tiles meet an abutting surface like a wall, a post or column, or a plumbing penetration. Typically, every tile floor should be protected with a perimeter movement joint to isolate the tiles from normal structural movement. As a single-room floor expands to two or more interconnecting rooms or hallways, each segment should be separated by an additional movement joint. A movement joint should also be located wherever two different backing materials meet, as in the case of an existing wood-frame floor enlarged, during a remodel, with a concrete slab.
A movement joint is simply a joint between tiles or between tiles and abutting surfaces that is filled with a resilient material instead of a hard caulk. On floor and wall installations, movement joints eliminate hard-surface contact that can damage the tiles, the structure, or both. Modern buildings are designed to move slightly, and if you install tiles to accommodate this movement, you should experience few problems or complaints. If, on the other hand, you set tiles directly against abutting surfaces, or fill joints in the movement zones with hard grout, or install crack isolation membrane systems without incorporating movement joints, you should expect to see cracked and powdery grout, cracked and loose tiles, split and leaky waterproofing membrane, ineffectual crack isolation membrane systems, and lots of call backs. In fact, movement joints are one of the secrets to building long-lasting tile installations. For best results, refer to EJ171 found on pages 68 and 69 in the latest TCNA Handbook.
How many? Where to locate?Numerous movement joints used in tile installations can be found under EJ171-05 in the latest TCNA Handbook. Of the seven types illustrated, all but one share the classic bow-tie sealant cross section that results from the use of a foam backup strip. The thinned out center section of this configuration allows the sealant to stretch and compress without destroying itself or tearing away from its sidewalls. The joints depicted in EJ171 have a practical size limitation since backer rod strips smaller than 1/4-inch diameter are generally not available. For this reason, most residential movement joints are filled with a resilient caulk without the backer rod. Another reason that residential movement joints are usually made without backer rod and bond-breaking tape is frequency. Because of the size of the typical floor, residential movement joints are normally only found around the perimeter where they are often obscured by wood molding or other trim. On larger commercial floor projects, movement joints are often located running across the width of the floor where they are subject to foot and wheeled traffic and need stronger construction than what is adequate for residential work.
Joint width and frequency are important factors. On residential work, the minimum acceptable movement joint width is 1/8-inch with 1/4-inch preferred for glazed wall tiles, and 1/4-inch wide for all other interior tiles. Exterior joints, because of contact with the direct rays of the sun, and because of wide temperature swings, can run from a minimum width of 1/8-inch to 3/4-inch. EJ171 offers a formula for determining the most appropriate joint width. Frequency-how often movement joints are placed-is based on size and location with exterior tiles requiring more movement joints than interior-installed tiles. It is important to note that the requirements for interior tiles exposed to direct rays of the sun (or moisture) are equal to exterior tiles. These joints should be placed every 8 to 12-feet in each direction.
PerformanceAs an installer, I depend on a network of movement joints to help protect the tiles, the structure, and any waterproofing or crack isolation membrane systems that are a part of the tile installation. I also want to reduce call-backs due to grout cracking that occurs when the laws of physics have their way with a structure, and a crack appears in a movement joint that was filled with grout instead of a flexible sealant or caulk. Movement joints do not eliminate movement, but instead, provide the space and the means for normal movement to occur unnoticed and without causing damage. A good example of the need for a high-performance movement joint is a Spectrum award-winning installation that features a porcelain mosaic inlayed into a wood strip floor.
Consumers often complain-and rightly so-about cracks between tiles and other finishing materials, and between tiles installed on adjoining walls. Yet, producing attractive, invisible movement joints is relatively simple. For this installation, once the routed wood edges tiles were finished and given protective coats of sealer, and once the tiles were installed and grouted, the first step was to ensure that the 3/16-inch movement joint slot was open and clean. The next step was to fill the empty joint with 1/4-inch backer rod to a height approximately 1/4-inch below the surface of the tiles. This challenging installation posed many obstacles, not the least of which was placing the backer rod at the exact height. Nevertheless, in spite of the claws of one of the inhabitants of this house (a feisty black lab), the goal of this particular movement joint, now 5 years old, have been met: no appearance of even a single crack between the tiles and the hardwood flooring.
Operating life of a movement joint?Movement joint fillers are like the tires and drive belts on the most modern automobiles: Although the tiles and other installation materials may last the life of the building, the movement joint fillers will have to be removed from time to time. The length of service depends on numerous factors including: frequency of use, interior/exterior, type and frequency of maintenance, exposure to water, exposure to sun, filler materials, etc. With all new materials, the average movement joint filler installation should last 5-10 years for interior work with a year or two less for exterior applications. As with any other installation material, using premium movement joint fillers should provide increased longevity.
Resources used in article:
Illustrations are courtesy of TCNA.
Photos are courtesy of Mike Mesikep.
Copies of the TCNA Handbook can be purchased from the TCNA at www.tileusa.com