Scratch and Leveling Coats
Over rough-surfaced backings, a level surface to receive tile may be built up with portland-cement mortar. For walls and ceilings, the mortar mix for the scratch and leveling coats for application to metal lath, concrete, or masonry should be 1 part portland cement and 3 parts dry sand or 4 parts damp sand, by volume. The ingredients should be mixed dry. Then, sufficient water should be added to make a stiff mix. The scratch coat should be cured for at least 24 hr.
A leveling coat is desirable when the surface of the scratch coat varies more than 1â„4 in in 8 ft from the required plane or when the required mortar-bed thickness exceeds 3â„4 in. As for the scratch coat, the leveling coat should be scratched and cured before the next bond coat is applied.
Mortars and Adhesives
For setting ceramic tile, portland-cement mortar is the only type recommended by the Tile Council of America for a thick bed. Other mortars and adhesives should be used only for thin beds. Setting materials such as epoxies and furans that do not contain portland cement offer special properties but are more expensive than cement-based mortars.
Portland-Cement Mortar. This is suitable for most surfaces and ordinary installations.
For floors, the mix may be 1 part portland cement and about 6 parts sand.
For walls, about 1â„2 part of hydrated lime may be added to the floor mix. The bed may be 3â„4 to 11â„4 in thick. Tiles may be set into the bed while the mortar is still plastic (ANSI A108.1). Or, after the mortar has cured, the tiles may be bonded to the mortar bed with a 1â„16-in-thick coat of dry-set or latex portland-cement mortar or with neat cement. If a neat-cement bond coat is used and the tile is absorptive, it should be soaked before being set. (See Fig. 11.29a, d, e, Æ’, g, and i.)
Dry-Set Mortar. This is a mix of portland cement and sand, with additives that impart water retentivity. The mortar should meet the requirements of ANSI A118.1 or A118.2. Applied as a coat as thin as 3â„32 in, the mortar is suitable for use on stable backings with true surfaces (Fig. 11.29b and h). Tile installation should be in accordance with ANSI A108.5 or A108.7.
Latex Portland-Cement Mortar. This is a mix containing portland cement, sand, and a latex additive, prepared to meet requirements of ANSI A118.4. Tile applications and installation method with this mortar are similar to those for dry-set mortar and should be in accordance with ANSI A108.5. (See Fig. 11.29b and h.)
Early exposure of latex mortar to water inhibits development of full strength and increases sensitivity to water. Hence, for applications such as swimming pools and showers, the mortar should be cured at least 14 days and allowed to dry thoroughly before exposure to water.
Organic Adhesive. This is an organic material that cures or sets by evaporation.
It should meet the requirements of ANSI A136.1. Applied in a thin layer with a notched trowel, organic adhesive is suitable for use on stable backings with true surfaces, but not for swimming pools or exterior applications. Tile installation should be in accordance with ANSI A108.4.
Epoxy Mortar. Suitable for use where chemical resistance, high bond strength, or high impact resistance is needed, this mortar contains epoxy resin and hardener and meets requirements of ANSI A118.3. It should be applied as a thin coat in accordance with ANSI A108.6 (Fig. 11.29c).
Furan Mortar. Suitable for use where chemical resistance is important, this mortar consists of furan resin and hardener. It should be used in accordance with the manufacturers recommendations.
Grouting Materials for Tile. After tile has been set, the joints should be grouted.
Most grouts have a portland-cement base but are modified to provide specific qualities, such as whiteness, uniformity, hardness, flexibility, or water retentivity. Damp curing of such grouts for about 72 hr is required.
A grout mix may be prepared in the field with portland cement and a fine graded sand, with up to 1â„5 part lime, if desired. The ratio of portland cement to sand, by volume, may be as follows: 1:1 for joints up to 1â„8 in wide; 1:2 for joints up to 1â„2 in wide, and 1:3 for joints wider than 1â„2 in. Prepared cement-based mixes include commercial portland-cement grout and dry-set grout. A latex portland-cement grout may be prepared by adding latex to any of the preceding mixes and offers the advantages of lower permeability and no curing, but it is less rigid than regular cement grout.
Grouts also are available with mastic, furan, epoxy, or silicone rubber, to provide such properties as flexibility, stain resistance, high impact resistance, and capacity to withstand below-freezing temperatures and hot, humid conditions. Such grouts, however, are more expensive than the cement-based ones.
