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Spot Bonding: A Growing Problem

In my previous career as a tile contractor and quality control consultant, I’ve managed well over 1,500 projects in the DC/MD/VA area.  Spanning over a decade – working closely with labor, design, and building professionals, I’d like to think I’ve seen just about everything in this industry; the good and the bad.

In the world of construction, evolution is a constant. New products and improved technology help promote increased efficiency and predictability of the finished system. From early design to final closeout, every step of the process is carefully measured and executed. The construction process requires this level of detail because as with anything else, the process is only as strong as its weakest link.

Obviously, this isn’t anything new. So, why am I standing on a soapbox and voicing this seemingly ubiquitous statement? Because, “knowing” and “doing” are completely different actions. That said, let’s bring this discussion to the world of tile.

Tile Evolution

The evolution of tile sizes has been significant in various industries, including architecture, interior design, and construction. Tiles are commonly used for flooring, walls, and various surfaces, and their size has evolved over time due to factors such as aesthetics, technological advancements, practicality, and design trends. From an aesthetic standpoint, today’s tile has much more range and versatility. Offerings include a limitless assortment of geometric shapes, textures, colors, patterns, and design possibilities.  At the same time, tile performs like never before. Technology allows for denser, stronger, and less absorbent tiles. Many tiles can withstand annual freeze/thaw cycles and are nearly impervious to moisture and water. Tile has become the “go-to” hard finish for commercial interior and exterior applications.

Let’s also talk about tile size. Advancements in production and technology allow for larger and larger tile sizes. In my early years, 12”x12” size tiles were considered “large format.” It’s true! My crews would complain about installing anything larger than 8”x8″!  Of course, they adapted and accepted the fact that tiles were evolving to larger sizes. These days, 24”x24″ and 8”x48” are the industry norm, and 12”x24”s are considered a commodity.

Here’s an overview of how tile sizes have evolved:

  1. Ancient Times: Tiles were relatively small and handmade in ancient civilizations like Mesopotamia and Egypt. These tiles were often used to create intricate mosaics, and their sizes were limited by the technology and resources available at the time.
  2. Roman Influence: During the Roman Empire, tiles became more widespread, and their sizes gradually increased. The Romans were known for using larger tiles, especially for their bathhouses and public buildings. These tiles were often made of terracotta or stone.
  3. Medieval and Renaissance Periods: Tiles continued to evolve in the Medieval and Renaissance periods. Intricate patterns and designs were created using smaller tiles, contributing to the development of mosaic art. However, the sizes of individual tiles remained relatively small compared to modern standards.
  4. Industrial Revolution: The Industrial Revolution brought significant advancements in tile manufacturing. This led to the production of larger and more uniform tiles. As machinery and technology improved, tiles could be produced in larger quantities and with more consistency in size.
  5. Modern Times: Modern construction techniques and materials expanded tile sizes. Larger tiles became popular for flooring as they reduced the number of grout lines and created a more streamlined appearance. Larger formats also made installation faster and more efficient.
  6. Square to Rectangular: A notable shift in tile design occurred when rectangular tiles gained popularity alongside traditional square tiles. Rectangular tiles can visually elongate a space and provide more design flexibility. This change in shape allowed for various layout patterns, including herringbone, brick bond, and more.
  7. Large Format Tiles: In recent years, large format tiles have become a design trend. These tiles can be as large as several feet in dimensions and are often used to create a seamless and modern look. Large format tiles are common in commercial spaces, high-end residential projects, and areas where a minimalist aesthetic is desired.
  8. Technological Advances: Advancements in tile manufacturing technology, such as digital printing and precision cutting, have enabled the creation of tiles with intricate designs and patterns. These technologies have expanded the possibilities for tile sizes and aesthetics.
  9. Future Trends: The evolution of tile sizes will likely continue, influenced by architectural trends, technological innovations, and sustainable practices. As design concepts and materials evolve, we might see even larger tiles, innovative shapes, and eco-friendly options.

In summary, the evolution of tile sizes reflects technological advancements, design preferences, and construction methods over time.

So, what is the point of explaining all of this? You may be wondering when I will get around to the topic of spot bonding. I’m getting there, but I needed to provide that brief history lesson for it all to make sense. As mentioned earlier, the construction system process is only as strong as its weakest link. Specific to tile, all the components that make up a finished tile system must be appropriate and installed correctly – per industry standards and methods. Any shortcut or misstep in this process will manifest in a faulty product. As tile manufacturing has evolved, so have the means and methods of installation.

In my experience, one of the main drivers that can make or break this system is the application of the mortar. For the purposes of this conversation, let’s stick to thinset mortar.

The Problem

As tiles become bigger and bigger, large segments of the labor force struggle to keep up with the technical installation skills required. Factor in the new generation of “user-friendly” thinset products now widely available, and the chances of encountering improper installation methods skyrocket, knowingly or unknowingly. One of the most common issues with improperly installing large format tiles is by way of spot-bonding.

Spot bonding is not a recognized method of installing any tile (no matter the size). Unfortunately, this method has become so prevalent that it’s considered one of the leading factors when large tiles crack, break, and de-bond.

What is “Spot Bonding?”

Spot bonding or “five-spotting” is placing globs or daubs of mortar on the back of the tile, typically at the corners and the center (five-spotting). This method is a ticking time bomb for failure and no longer becomes a question of “if” it will fail but “when.” This method does not fully support or bond the mortar to the substrate. Also, spot-bonding does not follow any established and proven installation methods, nor does the Tile Council of North America acknowledge it.

Damaged tile that was spot bonded
Mortar coverage in dry areas requires a minimum of 80%. The voids caused by the spot-bonding method lead to structural damage and hollow sounds. This tile was damaged when an elementary student accidentally bumped their lunchbox on it.
A minimum of 95% mortar coverage is required in this shower stall. Voids like this trap water and can lead to mold/mildew growth. In addition, the mechanical bond was weakened which lead to cracks in the tile.

Why do contractors use spot bonding?

The simple answer is that it’s easier and faster; place daubs of mortar on the backside of the tile and push into position until it’s flush with the adjacent tiles. Shortcutting like this typically means the contractor has eliminated substrate prep (which we all know is mandatory, not optional) and has likely avoided any conversation regarding lippage. Even when a tile contractor is under tight deadlines and aggressive timelines, spot bonding should never come into play.

Major Problems with Spot Bonding

Note the word, “major” in the above header. MAJOR problems with spot-bonding include:

  • Does not meet the mortar coverage requirement per Tile Council of North America and ANSI standards. If the spot bonded tile receives 30% mortar coverage, that’s 70% unsuSpot-bonding_Damagepported weight (gasp!), ultimately leading to damaged tiles.
  • Excessive voids under the tile reduce the overall modulus of rupture (strength of tile installed) thus lowering the overall breaking strength. Any concentrated impact loads will indeed compromise the structural integrity. Thinking about setting a 500lb refrigerator on this tile? Think again.
  • Hollow tiles = reduced load resistance.
  • Lighter color tiles may discolor, and will reveal spot marks.

The Correct Way

According to the ANSI Specifications, Section A108.5-2.2.2 describes the approved method for installing floor and wall tile as follows:

“Apply mortar with flat side of trowel over an area no greater than can be covered with tile before the mortar skins over. Using a notched trowel of type recommended by mortar manufacturer, comb mortar to obtain even setting bed without scraping backing material. Cover surface uniformly with no bare spots and with sufficient mortar to insure a minimum mortar thickness of 3/32” (2 mm) between tile and backing after tile has been beaten into place. Tile shall not be applied to skinned-over mortar.”

Using the above ANSI method, the mortar is keyed into the entire substrate resulting in an excellent mechanical bond with minimum voids.


Tile installation methods will forever evolve and change. Newer technology in thinset, grout, and membranes continue improving the process. However, spot bonding, in any form, is not a recognized method of tile installation and should never be used. Always follow the recommendations of ANSI A108 for all tile installation methods.

  • Properly clean the substrate and dampen it if needed.
  • Properly key in your mortar to the substrate with the flat side of the trowel.
  • Comb the mortar in one direction – play it straight!
  • Place the tile into the mortar, moving it back and forth, perpendicular to the trowel ridges. This motion allows the mortar to collapse fully, eliminating voids and transferring the right amount of mortar to the backside of the tile.

Lastly, write in the tile specification that spot bonding is not an acceptable installation method for your next project.

As always, send any questions or comments to our QA&T Team – we are here to help.