Luan is a type of plywood manufactured from hardwood trees harvested from the Philippines, Malaysia, Indonesia and Thailand. Felled trees are placed on a rotary and thin sheets of plywood are peeled from their trunks as they turn. Luan trees are native to the Philippines and have lent their name to the tropical, imported plywood that is actually made from a number of different trees. Luan is also called lauan, meranti and serai.
Many installers have their own ideas and techniques regarding tile substrates. The subject of luan, however, is one many professionals agree upon; they don't use it. In fact, according to the American National Standards for the Installation of Ceramic Tile, luan is not recommended for use as tile backing.
Oils in Luan
Luan contains oils that repel the moisture in thin-set, resulting in a poor bond or no bond at all. The technical term is "delaminating" and it refers to the thin-set peeling away from the substrate. As a result of delamination, tiles crack because they have only partially bonded to the substrate or they pop off the plywood altogether.
Expansion and Contraction
Another problem with luan, as with all plywood, is that is expands and contracts with changes in moisture. This movement happens at a different rate than the expansion and contraction of the tile. When the two surfaces are flexing at different rates, the tile can crack or come away from the plywood.
Cement Backer Board
Cement backer board is the most common substrate used for tiling. It is water-resistant and bonds well to tile. Cement backer board is not structural; it just facilitates tile adhesion. Use 1/2-inch backer board for all wall installations and 1/4-inch boards for floors. Apply a layer of thin-set between plywood subflooring and backer board to ensure no gaps exist between them that might cause movement. Secure the backer board with 1 1/4-inch underlayment nails and proceed with tiling.
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