Why Are the Porcelain Floor Tiles Popping?

The House

• Few houses are anchored in bedrock as buildings are engineered to move with the earth beneath them. Depending on the age of your house, its foundation and floor joists may shift. If sills -- the thick timbers upon which the house sits -- have sunk or rotted, it will move even more. Floor joists move and, with them, the sheets of plywood attached to them. Over time the floor becomes an uneven relief map that shows joists and traffic patterns. The larger the pieces of tile laid over such a terrain, the more likely they are to pop up due to uneven base, or substrate, and incomplete seals.

Substrate

• To solve the problem of uneven or shifting floors, a layer of plywood or cement backer board (CBU) is laid over the floor to receive the tile; cement board is more expensive but works best in bathrooms, kitchens or other applications where moisture might warp plywood. It establishes a level substrate because it is tacked along the joists, not the valleys, of the floor and moves with the house, not the various parts of the floor. When wood backerboard gets wet and swells, twists from improper attachment, or is laid over an extremely uneven floor without additional leveling, tiles may pop up.

Installation

• Porcelain is hard, dense and the same color throughout, making it less likely to break or show scratches. Each tile manufacturer recommends a particular type of adhesive to use with tiles. Mud adhesives form a thick sea of mortar into which tiles are set and leveled, and thinset adhesives fill a thinner space between the tile and backerboard. The adhesive recommended by the manufacturer, applied properly and allowed to “set up” before grouting, will hold tiles firmly. If the wrong adhesive is used, it is improperly applied, allowing air pockets to form, or it is grouted before it has set up, tiles may become delaminated and begin to slide and expel chunks of grout, finally popping up.

Tile

• Porcelain tile is the most expensive type of ceramic tile, but it is a bargain compared to marble or stone because it can be made to resemble either one. One common mistake made in choosing tile, though, is to put tile manufactured for use on a wall on the floor. Wall tile is not as durable, scratch resistant or slip resistant as floor tile. It may also be more absorbent, although porcelain is more impervious than other ceramics. Manufacturers mark tile by class; classes 3 through 5 are suitable for use on floors. If class 1 or class 2 wall tiles are used on floors, they may pop up but are more likely to crack.