Tile & Stone Installation

Southcrete™ 28 Flexible Mortar Additive (SC28)

Southcrete™ 28 is a unique acrylic additive, which, when added to SGM Premium Thin-Set Mortar, creates a super flexible mortar that will bond to many “difficult to bond” substrates. This system gives superior flexibility which permits the mortar to bridge minor cracks up to 1/16″ in width on the same plane. Southcrete 28 is ideal for use with glass tile and mosaics.

Product Details


Southcrete™ 28 may be used to set both vitreous and non-vitreous ceramic tiles for service requirements of residential and light commercial use. Applications include vertical or horizontal, both interior and exterior over properly prepared concrete, mortar beds, cementitious backed units, (APA) exterior grade plywood (interior use only), existing ceramic tile and stone, gypsum wallboard, steel existing cutback adhesive, vinyl tiles (residential and light commercial only), and smooth concrete.


Do not use for the installation of green, red, or black marble, or agglomerate tiles. Install only when temperature is at least 50°F (fifty degrees Fahrenheit). Do not use over any of the following:

  • Particleboard.
  • Luan plywood.
  • Hardwood or parquet flooring.
  • Gypsum-based underlayments.
  • Drywall or plaster on exteriors.

Do not use in areas subject to inclement weather within 48 hours after installation. When using Southcrete 28 premium thin-set mix in any area that will be wet continually (shower receptors, swimming pools, et cetera) allow mortar to cure a minimum of 14-days prior to any exposure.


Concrete: Floors must be 28 days cured and free of moisture. Floors must be free of any wax, oil, dust or paint overspray. Hence, any further cleaning shall be done using SGM Safe Clean Crystals, refer to Safe Clean label directions. Remove all liquid curing agents. All materials and areas to be tiled should remain above 40°F (forty degrees Fahrenheit) 24-hours prior and 72-hours after installation.

Plywood and Wooden Substrates

  1. All plywood shall be free of dust, oil, and any other foreign matter.
  2. The typical floor or other systems shall consist of joists spaced not over 16″ O.C. and a subfloor of ?” or thicker plywood or 1″ nominal boards.
  3. All floors shall be engineered so that the floors maximum deflection under normal or full load does not exceed 1/360 of span.
  4. A ¼” gap shall be left around all vertical surfaces, also a ¼” gap shall be left between sheets of wood to allow for expansion.


Detailed installation procedures may be found in the TCNA handbook and ANSI 108.5.

  • Concrete and Cement Subfloors: All floors must be 28 days cured and free of moisture. Floors must be free of wax, oil, dust, or paint particles. Hence, any further cleaning shall be done by sanding or using SGM Safe Clean Crystals (sulfamic acid). Remove any liquid curing agents or concrete sealers.
  • Plywood and Wooden Subfloors: All plywood shall be free of dust, oil, and any other foreign matters. The typical floor or other system shall consist of joists spaced not over 16″ O.C. and a double subfloor of ?” or thicker plywood or 1″ normal boards. All floors shall be engineered so that the maximum deflection under normal or full loads does not exceed 1/360 of the span. A gap of ?” — ¼” shall be left between top sheets of wood.
  • Alternate Subflooring: To bond over existing ceramic tile, marble and resilient flooring, floors must be bonded well to its subfloor and free of any wax, oil, dust, or paint particles.


SGM premium thin-set mortar should be added to approximately two (2) gallons of Southcrete 28 Flexible Mortar Additive (undiluted). Mix thoroughly to a smooth paste-like trowelable mix, allow mortar to slake ten (10) minutes, then remix while using a mechanical mixer, not exceeding 150 rpm, so not to entrain air in the mortar. Do not add additional latex after mortar slakes. Do not re-temper mortar after initial set in the bucket, discard and mix fresh materials.


Apply the mortar liberally with the flat side of a trowel. Use sufficient pressure to work mortar in good contact. Then comb with the notched edge of the trowel to leave uniform edges. Place tile while the surface is wet and tacky. Spread only as much mortar as can be covered in 15 to 20 minutes or before surface dries. Place tiles with a twisting motion and beat lightly, before initial set takes place, to fully embed in the mortar. Mortar that has formed skin should be re-troweled before applying tile. Use proper sized notched trowel (see diagram) to ensure 100% coverage of mortar to tiles and substrate. Some irregular tiles require back-buttering. Industry standards require approximately 3/32″ to ?” mortar bed thickness after beat in.


Mortar will obtain a minimum cure within 12—24 hours, depending on atmospheric conditions. Normal grouting can be done 48 hours after tiles have set.


Coverage will vary depending upon the type of tile, substrate and whether or not back-buttering is required.

Coverage is based on a 50 lb bag of thin-set mortar and two (2) gallons Southcrete 28 liquid.


  • Trowel Size: 50 lb bag
  • 1/4 x 1/4: 75
  • 1/4 x 3/8: 65
  • ½ x ½: 40


Meets or exceeds ANSI 118.4 requirements when mixed with SGM’s thin-set mortars.


One (1) year in unopened properly stored container.


EYE IRRITANT! During mixing or application, avoid contact with eyes. In case of such contact flood eyes repeatedly with water and CALL PHYSICIAN. Wash thoroughly after handling and before smoking or eating. Do not take internally. Harmful if swallowed. Do not induce vomiting. Call physician immediately. KEEP OUT OF REACH OF CHILDREN!

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 product 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.