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Unread 07-03-2020, 08:29 AM   #1
fhueston
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Tile Bond vs Coverage

Thought the following might interest this group

Tile Bond Vs Coverage
Frederick M. Hueston, Stone Forensics

Experienced installers and inspectors are aware of the requirement for coverage on stone and tile installation. ANSI requires an 80% coverage in dry areas and 95% in wet areas for ceramic tile as follows:

ANSI A108.4- Installation of tile for floors and countertops
A-4.2.2.4.2 Thoroughly beat all tile or tile assemblies into place with a beating block to obtain maximum contact of adhesive on the back of each tile, or back of each tile and back mounting material, and not less than an average contact area of 80% except on shower installation where contact area shall be 95% when no less than three tiles or tile assemblies are removed for inspection.
Many local and state codes also require the same coverage.

Natural Stone guidelines set by The Natural Stone Institute and the Tile Council of North America require 95% coverage in all areas.
So coverage is nothing more than the amount of setting material touching the back of the tile. No where in the industries guidelines does it state a percentage of bond.
Bonding is defined as something to join two things together. In the case of tile setting it would be to join the tile to a substrate via an adhesive.
But is coverage and bonding the same. I would argue that the two are not necessarily the same or in some cases not even related.
For example, a tile set in a sand bed would have 100% coverage but zero bond. On the other hand a quarter size dot of epoxy on the back of a tile would make it almost impossible to pull up which means it has a good bond.
As long as the proper adhesive is used a high coverage percentage can have a high bond strength, but experts need to be cautious when describing tile failures and not to confuse coverage vs bond. This is something I run across all the time where experts confuse the two terms.
As many experts are aware there all kinds of bond failures that do not relate to coverage. Some examples are as follows:
1. Incorrect setting mortar or adhesive. This is especially true when standard thin sets are used on resin back tiles.
2. Bond breakers on the tile- Dust, sealers, curing compounds and other materials that can interfere with bonding often result in lack of bond
3. Skimming over- This is when thin set mortar is applied to the substrate and it starts to cure before the tile is set.
4. Improper mixing- Improper mixing of the setting mortar and/or adhesive can result in poor or no bond
5. Flash setting due to hot substrate
6. Improper beat in
7. Failure to clean back of the tile
8. Improper dilution of additives in the setting mortar
These are just some of the common reasons for bonding failures. Non of them can be contributed to coverage.
Failures that can be caused by poor coverage are the result of voids in the setting mortar or adhesive and can include:
1. Cracking
2. Hollow sounds
3. Water intrusion in the voids of the setting mortar
These failures are related to coverage but not to bonding.

In conclusion one needs to be aware of the differences between bonding and coverage failures.
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Unread 07-04-2020, 09:42 AM   #2
Dave Gobis
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In addition to what you mention less we not forget there are over a 100 thinset formulations out there used for bonding tile with countless variations in absorption and other attributes. Bonding has established minimum values under product performance. Chasing bond value versus coverage is going down a big rabbit hole other than the obvious visual defects.

Let's talk about burnished slabs, my current favorite subject. Now there is something that often gets written off as curing compound.
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Unread 07-07-2020, 12:28 PM   #3
Steve Taylor
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Also, remember that you should not pick out sections of the ANSI standard and ignor the rest. There are ANSI standards for bond strength that rely on full coverage. It is important to have the right mortar AND get full coverage.
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