CTEF Tile Tip: Expansion Joints -- Are They Necessary?
Most people will agree that buildings experience significant movement on a day-to-day basis. Accommodating this movement is crucial for a successful installation of ceramic, porcelain and/or glass tile. Although there are many causes for movement in a structure, temperature and moisture changes play a large role.
Tiled floors can move significantly when affected by heat. The source of this temperature swing may be a result of the increasingly popular use of in-floor heat. In this case, the floor tiles will expand as the electrically heated cable (or the tubing which carries water heated by a boiler) varies in temperature. When the heat is on, the floor expands. When the heat cycles off, the floor cools and contracts.
Another often unconsidered source of heat is sunlight. The sun shines brightly, causing the floor to expand. When the sun is hidden by passing clouds, the floor cools and contracts. The movement is much like the action of an accordion, with the in-and-out motion similar to that of a floor expanding and contracting many times per day.
This resulting expansion and contraction must be accommodated or the tile assembly may rebel by shearing away from the substrate and moving upward in what is known as “tenting.” The attached photo demonstrates the unfortunate result of tile installed with nowhere to go…but up. This job was a large tiled area between elevator cars and 16-ft. floor-to-ceiling windows with southern exposure. There were no expansion joints in the field tile and no perimeter joints along the elevator wall or the window wall. Hot sun plus a large tiled area with no allowance for movement is a recipe for failure, as seen here.
The tile industry has done a good job of providing guidelines, in the American National Standards Institute (ANSI) publication, designed to handle this movement. The ANSI book provides several guidelines which must be followed to ensure a long-lasting tile installation.
The ANSI A108.01 document provides the following standards:
Section 126.96.36.199—Interior areas exposed to direct sunlight shall have expansion joints spaced at 8 to 12 ft. (2.4 to 3.5 meters). These joints are necessary in both north/south and east/west directions.
Section 188.8.131.52—Unless otherwise specified, use sealants complying with ASTM C920, which designates sealants according to types, grade, class and uses. Back-up strip shall be a flexible and compressible polyurethane, and rounded at surface to contact sealant…It must fit neatly into the joint without compacting, to such a height as to allow a sealant of half the width of the joint. Sealant must not bond to the back-up material.
Additionally, ANSI A108.02, Section 4.4.2 states: “Movement joints area are a requirement for tilework.”
Armed with this information, the installer can ensure the finished installation will look great, with plenty of room for expansion and contraction.