According to ANSI A108.01-2.4, 2005, tile can be installed over horizontal and vertical building surfaces that are "sound, clean, and dimensionally stable."
"Sound" means that the surface is stable and well cured in the case of concrete surfaces. "Clean" means that the intended surface is free from surface contaminants that would affect the bond strength of the tile. "Dimensionally stable" means that the framing and supporting members are sufficiently constructed to support the installation.
How do we ensure that our project meets these recommendations? First, we put these specifications into a contract. Then we insure that the project meets the specifications through inspection. Inspection means that we closely look at the job to ensure that framing members are the correct size and are spaced and nailed properly. We also ensure that if the framing members are covered with plywood or gypsum board, that it is installed correctly. In the case of cabinetry, that it is installed correctly.
Next we would ensure that the installations are level or plumb and true to plane according to the specifications. We would also ensure that rooms and enclosures are square or at exact right angles with each other. The basic rule is that framing and surfaces need to be level, plumb, and true to plane within 1/4″ in 10 feet (For stone installations, MIA recommends 1/8″ in 10 feet).
To check for level or plumb, a spirit level works very well. I use a 6-foot level for floors and walls where space permits and smaller levels when necessary. To check a surface for "true to plane" a level or straight edge can be used. Running it along the intended surface noting any deviation or high or low spots will do the trick. Checking for square can be accomplished by the use of a hand held square. The other way is mathematical in nature and is called the "3-4-5" method. For more on these methods and their application, go to the Estimating/Layout section.
Tile Doctor Tip: There are many great new laser measuring tools available for the tile contractor/installer. Laser squares which transmit a beam to form a perfect square on the floor or walls to rotating self leveling lasers for checking a floors on-plane requirement are available.
Wow! Wouldn't it be great if we could start from the ground up? This would mean that we could specify huge joists with close spacing and very strong wall framing and the like? Well, sometimes that is possible. Most of the time, we are subject to budget, time and skill constraints. Nevertheless, in each specific section we will discuss the minimum standards necessary to achieve satisfactory results. Lets look at some basic industry standards for surfaces intended for stone or ceramic tile.
Concrete or Masonry:
ANSI recommends concrete or masonry to be "dry, structurally sound, and free of wax, curing compounds, or other coatings." The surface needs to be flat without deviation exceeding 1/4″ in 10 feet or 1/16″ in 12 inches. In addition, the surface needs to be free of cracks or voids. The surface should have a steel trowel and fine broom-finish.
How do I check for surface contaminants? A simple method is to place water on the concrete surface and watch to see if the concrete readily absorbs it. If it is readily absorbed, the concrete is free of obvious contaminants that might adversely affect the bonding of tile. The absolute best way to ensure that a slab is ready for tile is to sandblast, bead blast, or scarify it.
What about cracks or voids in new or existing concrete slabs? Basically, all cracks and voids need to be repaired prior to the installation of a tiled surface when the tile is being directly bonded to the concrete. Unsuppressed cracks can and will transmit from the slab up through the finished tile surface.
There are two types of cracks. Shrinkage or minor meandering cracks can be repaired with any number of "crack-suppression" products available.
These minor cracks will be narrow and will not have a height difference from one side of the crack to the other. Large wide cracks that do have a height difference are structural cracks requiring a method other than a direct bond.
Voids can be filled with any number of floor leveling compounds currently available.
Tile Doctor Tip: When using crack suppression or leveling products, follow the Manufacturers instructions carefully for their use. In the case of leveling compounds mixed by the user, the water content is critical as the amount of shrinkage is dictated by water content.
Generally speaking, floor joists need to comply with the standards established by local codes or the Uniform Building Code. Their dimension or size determines the spacing. Normally, joist will be spaced 16″ on center. However, joist can be found 24″ on center. Again, size, design, and codes determine this spacing. Wall studs, whether wood or steel, are spaced 16″ on center. However, wall studs can be found spaced 24″ on center.
Wood framing, whether covered or not, needs to be structurally sound and be able to support the installation. In new construction, the framing can be specified to support the installation method chosen. For installation methods, go to the section in The Tile doctor that details the specific area you wish to tile.
Existing or Remodel Construction
The same rules should be followed in remodeling. The major difference is that the benefit of specifying the concrete, masonry, or wood framing is not present. There is a bonus to existing structures. The bonus is that the wood framing has had time to settle and stabilize. Meaning that future movement is generally minimal.
Concrete or Masonry:
As long as the surface complies with the structural requirements, the only concern is whether it can receive a direct bond or not. This will depend on whether it has surface coatings that would prevent a good bond. Coatings such as paint, curing compounds, grease, or oil should be removed. The same rules concerning cracks or voids should be followed.
The same rules apply to joist and stud spacing. In the case of existing structures, it might be necessary to repair or strengthen the framing to adequately support the installation.
Why do we write so much about framing recommendations and stable surfaces to receive tile? The reason is that when tile is applied properly, the project will perform and last, as it should. Conversely, when tile and the other related materials are either installed improperly or installed over inferior surfaces, the installations will fail.