Bulletin #11

Revised January 22, 2009

Installation of Marble, Stone, Thin Bricks and Tile That Resembles Brick, by the Ceramic Tile Setters Method

Definition of Materials

Natural marble tiles, thresholds and sills are being installed today by both the thick-bed method (conventional Portland Cement mortar) as well as by various thin-bed methods. Cultured (man-made) marble is usually installed by thin-bed methods over selected back-ups.

"Thin" stones and tile that resemble brick, are also installed by both thick and thin-bed methods. Natural Thin Stones (nominal 1/4-3/8" thickness), real clay bricks (nominal 1/2" thickness) and some Portland Cement bricks and stones are used for both interior and exterior installations. Imitation stones and bricks for interior work are most commonly made from Portland Cement, gypsum, or polyester materials.

In all cases, the manufacturer must be consulted as to the suitability for the application of their product for the specific installation involved, especially with reference to use in swimming pools, exteriors and wet areas. A successful installation of all these products requires a thorough understanding of each.

Natural marble is not man-made. It is found in various areas of the world where upheaval of the earth’s surface produced the proper geological climate for marble formation. Marble is quarried in the form of blocks weighing as much as 15 tons. The block is then cut into slabs, and further cut, ground and polished into tiles, thresholds, or into larger units according to architectural specifications. A wide range of surface area dimensions is available in thicknesses from 1/4 inch to 2 inches.

Physical characteristics of marble vary from quarry to quarry and from vein to vein in individual quarries. During the cutting process, the "milk" and stearates used to wash the dust or debris from the saws may dry and/or accumulate on the edges or back of the tiles. If this is not removed during the original processing, or at the job site, this film will interfere with the bond of either the setting bed and/or grout.

When selecting the installation materials, make sure they are compatible with "both sides of the sandwich"! For example, Dry-Set or Latex-Portland Cement mortars bond well to clean marble as well as to Portland Cement back-up surfaces. On the other hand, most solvent emulsion (water-base) mastics bond well to marble and to most interior back-ups, but tend to stain light colored marble. Water in the mastic becomes trapped in the setting bed and the mastic cannot dry or set properly.

The liquids in the mastic (usually a combination of water and solvent) must dissipate into the back-up or into the air. If water resistant gypsum backing (W/R) board is used, suction is less than if conventional drywall is used. The polish or seal coat on the face of the marble prevents moisture from dissipating into the air, except through the joint. Grouting before the mastic cures may trap moisture and result in dark areas appearing on the surface.

Special solvent based mastics and polyurethane elastomers usually cure faster but may stain marble.

Why does some green-colored marble warp after installation?

Some green-colored marble may warp through absorption of water from the setting bed. (Water drawn into the stone is held to the crystals by surface energy. This force tends to widen the intercrystalline space and thereby expand the wet side.) Since it is difficult to predict when and where warpage will occur, many mechanics take the precaution of either soaking the marble tile prior to installation, or "Fogging" the floor and covering it with plastic for 72 hours after installation. The idea being to get as much moisture on the face of the marble as that on its backside. Others use non-staining, quick-setting epoxy.
Checking for staining is recommended before the installation is started.

A 2" aluminum foil butter cup (as used in restaurants), filled with the thin-bed adhesive desired, pasted on the back side of the marble will suffice. If a dark area appears on the surface of the marble in two or three days, choose another adhesive. (Plain water will show through on light colored marble almost immediately.) When installing these products, the preferred method is to apply the selected adhesive to the back-up surface with the flat side of the trowel first, to get a good mechanical bond. This is followed immediately by the notched edge to apply the desired thickness of the bond coat.

Back-buttering the tiles promotes the same good mechanical bond to the other side. Applying the tiles with pressure and a slight twisting motion is almost as good. Proper beat- n with a hard rubber float promotes good coverage and level surfaces, without any high corners.

Unless a specific veining pattern is specified, the installer may use a "blend", random pattern. It is bad practice to install marble tiles with "butt" joints. Tight joints may result in edge chipping. The recommended joint width is 1/16th - 1/8th inches. This allows the setter to accommodate minor variations in "squareness".

"Lippage" is a condition that occurs when tiles are installed by a thin-bed method over an uneven subsurface. Tiles may "lip", one edge higher than their neighbors, giving the finished surface a ragged appearance. In some conditions, a certain amount of lippage is unavoidable. As a general rule, the recommended maximum variation of the finished surface should be no more than 3/16-inch (5mm) cumulative over a 10´-0½ (3 meters) lineal measurement, with no more than 1/32-inch (1mm) variation between individual tiles.

Lab tests indicate that the bond of marble tile can be improved by the use of certain materials as follows:
a. Latex-Portland Cement mortar has shown the highest bond strength.
b. Modified epoxy emulsion mortars bond well but may stain light colored marble.
c. Dry-Set mortars (without any latex additive) have shown high bond strength.
d. Pure Portland Cement used on a conventional mortar bed will also result in good bond strength.
e. Organic adhesives are not recommended for exterior installations.
f. Medium Bed mortars.

Good materials deserve proper use, and the following procedures are necessary.
a. Since much marble is translucent, use only white Portland cement in the setting bed or thin-set bond coat.
b. 100% coverage of pure or neat coat and mortar between the marble tile and the surface to be covered. This includes proper
beat-in to close up grooves in the bed left by trowel teeth.
c. Surfaces of concrete must be heavily sandblasted, bush hammered, water blasted, and/or scarified (except limestone)
before installations are made.
d. Expansion/Control joints are needed.
e. Shelf anchors should be used every 8’ vertical to help hold the weight of heavy material on large sheer walls.
f. Wet the back of marble being installed in Portland Cement or on plaster spots to remove dust and retard the absorption of
moisture into the marble from the bed.
g. Using a Medium Bed Mortar will result in less if not “0-lippage”.

The following practices have been observed as having caused trouble. Avoid them.
a. Avoid the use of curing compounds on concrete slabs. They prevent proper bonding.
b. Using only spots of bonding material, or failure to beat-in and eliminate the grooves from the notched trowels. This results in
as low as 30% to 50% contact or bond strength. Moisture accumulates in these voids and causes leaching and other
trouble, such as freezing or frost damage.
c. Marble tile placed directly onto the bond coat with the layer of dust or a film left on the back of the tiles.
d. Use of primer coats of polyvinyl acetates or other soluble bonding materials to bond mortar to concrete surfaces that have
not been sandblasted.
e. Brushing a primer coat or wet slurry instead of buttering the back of the tile before installing.
f. Stacking large amounts of heavy material onto insecure bridges or supports. Collapse may result in injury and extensive
damage.
g. Oil is deadly to marble; stains it. (Oil-base caulk will sometimes stain marble.)
h. Keep traffic off of newly installed floors for at least forty eight hours. The slightest movement of tile during the initial set will
cause loose tile later.
i. Marble shall be selected for harmony of effect. Use care in blending color and veining of stone to produce a homogeneous
effect. If necessary, lay out the floor with loose tile before setting them. Make certain the owner realizes that marble, as a
natural material, often has wide variation in veining patterns and differences in shading.
j. Lippage can be prevented before marble tiles are installed by making certain subsurfaces are level. All cement, adhesive, and grout must be removed from the face of the marble tile immediately after the grouting procedure is completed.
Polish \ dry. Acid cleaning must not be used on marble tile.

Cultured Marble

When installing cultured marble, or so-called "man-made marble", or conglomerate marble, consult the bond-coat manufacturer concerning compatibility of the product selected. Organic mastic or epoxy materials usually give better bonds than Latex- Portland Cement or Dry-Set mortars.

Thin Bricks and Real Stone

Real clay thin bricks and real stone can best be installed using ceramic tile setting materials and methods recommended for vitreous tiles.Setting: Back-butter Brick using an approximately ¼ x ¼ notched trowel. Press on flat troweld substrate and then move back and forth for final set. Some manufacturers have colored adhesives that resemble mortar when they cure and are normally recommended for interior installation.

When a rigid adhesive is used, movement in the back-up may cause the tile to shear loose. Proper selection of back-up surface is very important for all exterior areas, as well as interior areas that may be exposed to high humidity or moisture. Back-ups such as exterior grade plywood, cement asbestos board, etc. will expand and contract when moisture gets to them, from either side. Failure can occur from excessive movement that is usually not the fault of the product or adhesive. Grouting: For best results using either a Bag method or Pump will create a better-finished product. Using the smear method is not suggested, (check with local trade practices).

Summary

Prior to the installation of any of the above products, understand thoroughly the product itself, the job conditions and ultimate exposure, and the suitability of the back-up surface provided. Pay attention to control joints as recommended. Select installation materials and methods that are proven, known to work without callbacks or failure. Consult the product manufacturer when in doubt!