Tile & Stone Installation

Glass Mosaic Tile (GMT) Thin-Set Mortar

Glass Mosaic Tile (GMT) Thin-Set Mortar is the ultimate one-step polymer fortified thin-set mortar specifically designed for outdoor and wet environments. GMT Thin-Set Mortar provides superior adhesion to glass, mosaic tiles, porcelain, ceramic, and natural stone. Its unparalleled proprietary formulation makes it the perfect choice for setting tile in swimming pools, spas, water features, and other areas with submerged applications. GMT Thin-Set White Mortar produces an ultra-white finish that will enhance the look of glass, mosaic tiles, and any translucent tile or stone. GMT is now also available in gray. For use in both commercial and residential applications.

Product Details



  • Concrete and Plaster surfaces: All areas should be twenty-eight (28) days cured and shall be structurally sound, clean, and free of any moisture, wax, oil, paint particles, curing agents, or foreign matter. The slab should have a steel trowel or broom swept finish. Remove any liquid curing agents or concrete sealers, followed by a clear water wash. Surfaces may be cleaned with sulfamic acid (SGM Safe Clean Crystals) then thoroughly flushed and neutralized. Concrete shall be free of any efflorescence and hydrostatic pressure. Test to confirm that concrete can absorb water by sprinkling water droplets. If water beads up and does not absorb into the substrate, scarify surface via mechanical abrasion with a Carborundum disk followed by a clear water wash. Test again to ensure that water is absorbed into the substrate before proceeding with the installation. Smooth concrete should also be roughened to ensure a mechanical bond. For hot and dry conditions, lightly dampen the surface with water leaving no standing water. When used to install tile in any submerged application (swimming pools, spas, water features, et cetera) allow mortar to cure a minimum of seven (7) to fourteen (14) days before exposure to water.
  • Plywood and Wooden Substrates: All plywood floors (including subfloors) shall be engineered to meet all ANSI requirements. All plywood shall be an exterior grade (for interior, residential, and light commercial use in dry areas only), free of dust, oil, or other foreign matter.
  • Alternate Surfaces: To bond over existing ceramic tile, marble, vinyl, VCT, and resilient flooring, floors must be bonded well to its subfloor and free of any wax, oil, dust, or paint particles. For use over existing ceramic tile, scarify surface of tile via mechanical abrasion with a Carborundum disk followed by a clear water wash. Do not use over vinyl, particleboard, luan plywood, gypsum-based underlayments, wall coverings, adhesive residue, masonite, metal, glass, plastic, or painted surfaces. Surfaces such as these will prevent bonding and should be covered with a cleavage membrane topped with a 3/8 inch to ¾ inch (9.5 to 19.1 mm) reinforced mortar bed for floors. Wait a minimum of twenty (20) hours before dry-set mortar may be applied to the mortar bed.

Glass Mosaic Tile (GMT) Thin-Set Mortar may be used for radiant heating system installations. Do not use to install resin-backed stone. Not recommended for setting green, red, or black marble. The green and black moisture-sensitive marbles must be set with SGM EGS Epoxy Mortar. Consult SGM technical service department for product and installation recommendations.


Product is alkaline on contact with water. Use paddle for mixing to avoid splashing into eyes or contact with skin. During mixing or application avoid contact with eyes. In case of such contact, flood eyes repeatedly with water and CALL A PHYSICIAN. Wash thoroughly after handling and before smoking or eating. Do not take internally. CONTAINS FREE SILICA — DO NOT BREATHE DUST. Prolonged exposure to dust may cause delayed lung disease (Silicosis).

WARNING: This product may expose you to chemicals, including silica, which the State of California recognizes as a cause of cancer. For more information, visit the Proposition 65 Warnings Website (www.P65Warnings.ca.gov). Use NIOSH approved masks at all times to handle silica dust. KEEP OUT OF REACH OF CHILDREN.


Add Glass Mosaic Tile (GMT) Thin-Set Mortar mortar powder to approximately 1½ gallons (5.7 L) cool, clean potable water per 50 lbs. (22.7 kgs) bag. Machine mixing with a slow speed drill and mixing paddle is preferred (250—350 RPM). Higher speeds are not recommended and will entrain air. Mix the two (2) components together thoroughly until smooth. The proper consistency is obtained when the mortar is applied with the notched trowel to the substrate and the ridges formed do not flow or slump. Allow mortar to slake for five (5) minutes, and then re-mix before use. Do not add any additional water, latex, or powder after the mortar has slaked. Re-mix mortar occasionally during use and discard after initial set in bucket.


Detailed installation procedures may be found in the TCNA Handbook and ANSI 108.5. All materials and effected areas should remain above 50°F / 10°C (fifty degrees Fahrenheit / ten degrees Celsius) or below 100°F / 38°C (100 degrees Fahrenheit / 38 degrees Celsius) 24-hours prior and 72-hours after placement. Apply mixed mortar liberally with the flat side of the trowel, using sufficient pressure to key into the substrate; then apply additional mortar with the notched edge of trowel leaving enough mortar to give 100 percent coverage with the back of the tile. Place tile while the surface is wet and tacky and spread mortar over an area no greater than can be covered with tile before the mortar skins over. Place tiles with a twisting motion and beat lightly before the initial set takes place to fully embed in the mortar. Mortar that has formed a skin should be re-troweled before applying tile. Some irregular tiles may require back-buttering. During the setting of tile, it is recommended to periodically remove a tile and check to see that sufficient transfer of mortar is being attained. Industry standards require a minimum of 3/32 inch (2 mm) mortar thickness after beat in. Do not adjust tiles after they have been set more than 10 to 15 minutes.

  • NOTE: It is suggested that a mock-up for the evaluation of surface preparation techniques and application be done by applying three (3) to four (4) tiles and bonding mortar from the actual installation. These tiles should be left to cure for three (3) to seven (7) days and then removed to determine if an adequate bond has been obtained before the commencement of the installation.

A ¼ inch gap shall be left around vertical abutments to allow for structural movement and filled with appropriate elastomeric sealant.


Water is all that is required to remove uncured mortar.


The minimum cure is reached in 12—24 hours. Setting may vary according to atmospheric conditions. Normal grouting should be done 48 hours later.



  • 75 sq. ft. per 50 lbs. when applied with ¼” x ¼” (6.4 mm x 6.4 mm) sq. notched trowel.
  • 65 sq. ft using ¼” x ?” (6.4 mm x 9.5 mm) sq. notched trowel.
  • 40 sq. ft. using ½” x ½” (13 mm x 13 mm).


Up to one (1) year from date of manufacture in unopened properly stored containers.


None required.


SGM, Inc. warrants this product will perform in accordance with its intended use for a period of one (1) year from the date of manufacture. Any claim for defective products must be submitted in writing to SGM, Inc., and samples of defect must be provided. SGM, Inc.’s sole obligation will be to replace any product determined to be defective by SGM, Inc. EXCEPT AS PROVIDED HEREIN, SGM, INC. MAKES NO OTHER REPRESENTATION OR WARRANTY OF ANY KIND, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR PARTICULAR PURPOSE. IN NO EVENT SHALL SGM, INC. BE LIABLE FOR DAMAGES OF ANY KIND OR NATURE, WHETHER ARISING BY CONTRACT, TORT OR OTHERWISE. SGM, INC.’S SOLE OBLIGATION WILL BE TO REPLACE ANY PRODUCT DETERMINED BY SGM, INC. TO BE DEFECTIVE.