I hope you don't use spot bonding or "five spotting" when installing ceramic tile. It's a problem that's high on the list of failure questions received by the CTEF offices when things go wrong.
In case you didn't read How to Correctly Trowel Mortar When Installing Tile? or you still think it's okay, let's review in detail why you need to eliminate even the thought of using spot bonding for your ceramic tile installation projects.
What do I mean by 'spot-bonding'?
Spot bonding either floor or wall tile places a glob or dollop of mortar (about the size of a golf ball) on the back of the tile. Doing so with larger sized ceramic tiles means placing a glob of mortar on each corner with one in the middle of the back of the tile and is commonly known as “five spotting.” This process fails every time because the majority of the tile is not supported or bonded by the mortar to the substrate.
Most times, the installer makes no attempt to key (physically force) the mortar into the back of the tile with the flat side of the trowel. This results in a questionable mechanical bond. The tile is then placed onto a dry, unclean, un-mortared substrate which doesn't encourage any type of mechanical bond to this surface which is absolutely essential.
Call it spot bonding or five spotting. This technique compromises every industry-recognized recommendation for the proper installation of tile. It does not follow the established and proven tile installation methods detailed in the TCNA Handbook and the ANSI Specifications.
Let's be clear:
Although various tile installation methods are used in different parts of the country (which may or may not be included in the TCNA Handbook) and may function without problems, spot bonding tile is not one of them.
Spot bonding creates bare spots or voids under the tile
Here is one of the many downfalls to the spot bonding method: bare spots or voids.
As you can see in the image below where the installer used spot bonding, there are bare spots in between the blobs of mortar. The installer “thought” he or she was getting good coverage. Clearly, it's not the case.
Mortar voids such as these in floor tile installations are fatal to the tile installer. They create hollow sounding tile or even worse, broken tile.
And, on walls in wet (shower) areas, mortar voids normally trap water which will slowly bleed out through the cementitious grout joint causing a temporary discoloration or dark joint. Although the discoloration goes away, most consumers find this unacceptable. As a homeowner, I would, too. The bad part of this situation is that the dark joints will return every time the shower is used.
Spot bonding ceramic tile leads to three major problems
The reason installers use spot-bonding to install floor tile, especially large format, is that it virtually eliminates lippage. With the mortar concentrated in these five areas, the installer can easily push down on the mortar spot and get it to flatten out with the adjacent tiles. Continuing to push down on the other three corners usually yields a lippage-free installation. Life is good, right? Wrong!
This mistake creates a number of problems which many times will be cause for a callback and/or potential failure.
- The number one problem caused here is the lack of support of the tile. Any point load, including a woman’s high heel, will cause the tile to crack.
- The second problem occurs when a hollow sound is detected in the area which has no mortar underneath. This is not acceptable.
- The last problem occurs when moisture collects in these hollow areas causing the grout to remain dark until the water has completely evaporated. If the tile is a natural stone, the moisture could permanently discolor the stone, not to mention the grout.
Although spot bonding with mortar may be easier to set tiles flat to each other during the installation, it’s only a matter of time before just the slightest force causes a failure!
Eliminate spot bonding! It is simply not recommended for installing tile.
Is spot-bonding on walls allowed in the TCNA Handbook?
Yes, but there are only four approved methods in the Handbook. Each one uses a very specialized epoxy mortar designed for interior wall applications, only in dry areas.
These TCNA Handbook methods include:
W215: Ceramic Tile over Masonry/Concrete
W260: Ceramic Tile over Cement Backer Board on Wood or Metal Studs (shown below)
W215 STONE: Natural Stone Tile over Masonry/Concrete
W260 STONE: Natural Stone Tile over Cement Backer Board on Wood or Metal Studs
Each of these four methods uses an epoxy mortar which is recommended by the manufacturer specifically for spot bonding while also following the epoxy manufacturer’s coverage requirements. Further, the Limitations section of these methods state: Will not withstand impact.
If installed over wood or metal studs, the maximum stud spacing is 16” on center.
The approved method for installing wall and floor tile calls for keying mortar into the entire substrate
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 yielding a good mechanical bond with no bare spots.
Spot bonding doesn't even come close to these industry approved methods.
Eliminate five spotting from your ceramic tile installation methods!
If you consider yourself a serious and professional tile installer, save yourself time, trouble and possibly financial loss by using the industry recommended method to spread your mortar. It should provide the necessary mortar coverage and keep problems away from your door and the money you have earned in your pocket where it belongs.
- Properly clean the substrate and dampen if needed
- Properly key in your mortar to the substrate with the flat side of the trowel
- Comb the mortar in one direction
- Place the tile into the mortar moving it in a back and forth motion, perpendicular to the trowel ridges.
Here are a few additional resources that discuss the pitfalls of spot bonding ceramic tile:
- Is Spot-Bonding Tile an Acceptable Installation Method?
- Marble tile Bathroom fail, Shower Repair. How not to install tile. (3:31 minute video)
- Spot Bonding—What Are the Drawbacks When Installing Tile or Stone?
Let me know in the comments about situations you've encountered related to spot bonding when installing ceramic tile.