The installation of ceramic tile is demanding work, but the results should be aesthetically pleasing and long-lasting, especially when the tile industry standards and best practices are followed. Unfortunately, some tile placers choose to create their own schemes that do not follow the American National Standards Institute (ANSI) requirements, the Tile Council of North America (TCNA) methods and details, and tile industry accepted best practices. The results of these actions most times are disastrous. The Miami Sandwich method, a prime example of one of these schemes, most likely originated in South Florida.
This tile installation can be flat with acceptable lippage between each tile, but underneath the tile lies the problem. Unfortunately, many of the tile placers do not know that the way they are placing the large-format tile (facial dimension greater than 23″ [584 mm]) does not meet accepted tile practices. This is how they were taught to place tile – and do it as quickly as possible – since they are being paid a low wage by the square foot.
The Miami Sandwich scheme
The Miami Sandwich is an attempt to meet two needs: fix an otherwise unacceptable concrete slab due to its being out of flat, and install the tile.
The process begins with spreading the thin-set mortar on the slab with a small, notched trowel, but not properly keying the mortar into the slab with the flat side of the trowel to achieve a good mechanical bond. At this point, a wet loose stucco mix, which is designed for use on a wall rather than on the floor, is loosely placed on the floor, maneuvered around with a mason’s pointing trowel, and roughly flattened. The stucco mix, which is not designed for this application, is not compacted to create a strong dense base for the tile. Thin-set mortar is then notched on the back of the tile in a random pattern and placed on the stucco mix. Using a rubber mallet and a level, the tile is then beaten into place so that it is flush with the adjacent tile and level.
The Miami Sandwich problems
Now the problems begin because this scheme produces a host of failure-ridden issues. Since the stucco mix is not properly compacted to yield a strong base to support the tile, it can be subject to point load failures caused by dropped objects or heavy rolling items such as a piano or refrigerator. The action of beating the tile into the wet stucco mix to get the tile flat and potentially level, drives the aggregate to the bottom and water to the top. The water is now positioned between the top of the stucco mix and the thinset on the back of the tile acting as a bond breaker that inhibits a proper bond. This lack of bond almost always results in hollow-sounding tile that consumers find objectionable.
Tile industry standards and methods
The firmly-established and recognized ANSI standards and TCNA Handbook method and details provide the installer with installation practices that have been tested and proven to work well. One of these is the TCNA Handbook method F112 Bonded Mortar Bed. Following are the ANSI A108.1A standards:
- 2.2.1 The mix ratio for the mortar is one part cement, five parts damp sand, and up to 1/10 part hydrated lime.
- 2.2.2 When mixed with water, the mortar shall be a “dry-pack” consistency and workability that will allow maximum compaction during tamping of the mortar bed. Dry-pack mortar shall be compacted and the surface finished to provide a stable base for the tile, such as can be obtained with a wood or magnesium float.
- 5.2.2 Before placing mortar bed, spread a very thin continuous coating of pure portland cement slurry on the concrete surface or dust a thin layer of dry portland cement on the concrete and wet it. Broom the pure portland cement slurry or the wetted portland cement dust to completely coat the concrete surface with a thin and uniform coating.
You can see that the Miami Sandwich scheme has some vague similarities to the approved ANSI and TCNA methods above, but it cannot match the proven effectiveness.
The result
Most times, after a qualified inspector who uses the ANSI standards and TCNA methods to determine that the Miami Sandwich does not meet these standards and methods, the tile and underlying mess must be removed and replaced. The tile industry again gets a black eye.
The remedy
Quality-oriented tile installers and other interested parties need to work together to eliminate this disease. The Technical Committee of the National Tile Contractors Association (NTCA) is currently working on a document that will address the problem with a cautionary statement that can be given to the design professionals and building owners to guide them in the right direction.
All images courtesy of Mike Weaver of Trendsetter Tile & Stone
Scott Carothers
Scott Carothers is the Acdemic Director for the Ceramic Tile Education Foundation (CTEF) and is responsible for the creation of the Certified Tile Installer (CTI) program, and is involved in the creation of the Advanced Certifications for Tile Installers (ACT) program as well as providing training to others in the tile industry.
Carothers has been involved in the ceramic tile industry for nearly 40 years and was the owner of a successful retail and installation firm prior to CTEF. He has served as President and Chairman of the Board of the National Tile Contractors Association (NTCA), Chairman of the NTCA Technical Committee, was named the NTCA Tile Person of the Year in 2005, and the NTCA Ring of Honor recipient in 2013. He is a voting member of the ANSI and the TCNA Handbook committees.
