Hollow Sounding Tile

Hollow Flooring Tiles and Water

Story usually starts out like this: “my tile floor got wet and now it sounds hollow when I tap on it,” and “it never sounded hollow before,” as if people go around tapping on their tile floors to make sure they don’t sound hollow. Sometimes a homeowner will notice that tiles sound hollow, or it may be a savvy contractor who walks around the floor bouncing a golf ball and marking tiles with tape. Often, this situation results in a homeowner who is convinced of a damaged tile floor, and an adjuster who believes that tile is waterproof and cannot be damaged by water. The answer is a bit more complicated.

Ceramic Tile Flooring Over Concrete

Tile, concrete and mortar are all waterproof right? Why do tile floors sometimes fail over concrete?

Slab Leaks

First thing that I always ask when a ceramic tile floor is claimed to have been damaged by water is: “did you have a slab leak,” and if yes: “was it a hot water slab leak,” and finally: “did the plumber find the location of the leak.”

An answer to any or all of these questions will not always solve the problem of determining a cause for hollow tiles, or prove damage. Answers to these questions are, however, helpful information that may be used in coming to an informed conclusion.

Slab leaks can cause ceramic tiles to detach from their substrate, especially hot water slab leaks. This makes sense if we consider how the bond between a flooring tile and a concrete slab may fail.

The failure of a bond between a flooring tile can happen in two ways: the failure can be either mechanical, or due to deterioration, or a combination of both. In the case of a slab leak, both causes are possible or even likely given the amount of water, temperature, thin-set used, substrate preparation, etc. For example, a hot water (or even a cold water) slab leak can cause expansion of the substrate, or it may result in the expansion of the ceramic tile floor if the tiles are clay based and not porcelain. If either the tile floor or the substrate expand more than the other, the shear force may cause the bond between the tile floor and its substrate to fail. This would be an example of mechanical failure.

This is often seen in homes with no source of water intrusion. Tiles become hollow or even “tent,” at times with an “explosive” sound. Over time, a concrete slab can shrink, or clay tiles may expand. In either case, when shear force builds up to the point where the mortar bond is no longer sufficient to hold the tile floor securely to its substrate, the bond will fail. This may occur with porcelain tile floors if an aging slab shrinks over time while the impervious porcelain tile remains the same size. Porcelain, being impervious, may not always bond well with thinset. This may also occur with clay ceramic tiles if the clay has expanded over time due to the absorption of natural ground water. In both cases, proper expansion joints may have prevented the floors from failing (please see EJ 171 in the TCNA Handbook).

So if a slab leak can cause hollow tiles, but tiles may become hollow without water intrusion, how can one know if a hollow tile was caused by a specific water event? The answer is: you can’t but it may not matter. If there is a higher concentration of hollow tiles in an area of a known slab leak it will be difficult, if not impossible to disprove a claim of water related damage. If the concentration of hollow tiles is consistent throughout the floor, it may be concluded that no tiles had been damaged by the water loss, but this still is difficult to prove definitively. In that case, the floor still needs to be examined closely for damage. Tiles should be checked for deflection and grout should be inspected for cracking and efflorescence.

Surface Water

Can water that flows over the surface of a tile floor cause that tile floor to become hollow? It’s possible, but in most cases, no.

Most ceramic tile floors in Southern California were installed with thin-set mortar over an on-grade concrete slab foundation. This does not account for upper level bathrooms, laundry rooms, homes on raised foundations etc., but it does account for the vast majority of tiled flooring area in So Cal.

Ceramic tile flooring installed over an on-grade concrete slab foundation is listed as Tile Council of North America (TCNA) installation method F-113. This installation method has been given a Res2 (residential 2) environmental rating. The Res2 rating is as follows:

Wet Area Guidelines, from the “TNCA Handbook for Ceramic, Glass, and Stone Tile Installation” © 2014. Environmental classification Res 2 (Residential Limited Water Exposure) page 41:

“Tile surfaces that are subjected to moisture or liquids but do not become soaked or saturated due to the system design or time exposure. If water proofing is desired, it must be clearly specified. Including areas adjacent to R3 areas. Examples: Floors in bathrooms, kitchens, mudrooms, laundry and foyers, where water exposure is limited and/or water is removed; some backsplashes, some wainscots, some countertops.”

The examples provided, “bathrooms, kitchens, mudrooms, laundry and foyers,” are examples of areas where surface water may be present on a consistent but not continual basis. The recommendation for Res2 use in bathrooms implies that a Res2 installation may withstand an occasional toilet overflow, otherwise, if it were to be assumed that a category 3 (black water) flow onto a Res2 installation may likely result in the floor’s failure, or the necessity to replace the tile floor due to bacterial contamination, the TCNA would have recommend a higher environmental rating for bathrooms, considering that toilet overflows are a fairly common event. This would be a consistent reading of TCNA’s literature, which provides recommendations based on the potential impact of other likely environmental conditions that may affect the integrity of a tile floor installation.

So in most cases, a surface water flow will not damage a tile floor; but is this always the case?

No, tile may become damaged due to water intrusion originating from a surface flow. If water gains a pathway underneath a tile floor, the water may soak into the concrete causing it to expand. In most cases, when a surface leak causes a flooring tile to become hollow, there had previously existed some problem with the tile installation. The tile may have been installed over paint over-spray, or an existing vinyl floor. The thin-set may not have been mixed properly, or the mortar was old or defective. The ph balanced of the water used to mix the thin-set was off, or it could have been the ph of the concrete slab. Many times the floor was already hollow, which allowed water to freely flow underneath the tile, resulting in the worsening of a pre-existing condition.

Ceramic Tile Flooring Over a Wood Sub-floor

A wood substrate adds a moisture sensitive component to a tile floor installation.Ceramic tile floors should be installed over wood sub-floors with an expectation of a reasonable amount of moisture contact during normal use. For example, a ceramic tile floor installed in an upper level master bathroom should be installed to withstand dripping water and wet feet from a shower and the possibility of a toilet overflow. However, a wood substrate can be vulnerable to water intrusion. There are several ways in which water may damage a tile flooring installation when installed over a wood substrate.

Prolonged Saturation

This is a common claim, but usually there’s something else going on. If a tile floor is saturated for a length of time, it is possible for moisture to leach into the substrate through the grout. This is a possibility, and a common claim, but there’s usually another entry point for moisture to intrude into the substrate, an easier path than through the grout. Also, it may be that the tile floor was already hollow, thus providing an easy path for water to follow. I have heard it many times: “the water was two inches deep and it was like that for hours.” I’d like to see someone recreate this scenario in a home. Water doesn’t just stay put, and as soon as it flows out, it becomes no more of a problem for a tile floor than a good mopping. What is more likely problematic is where the water flows to. The water will soak walls, baseboards and cabinets. Water also may gain access to the wood substrate through openings at toilets, cabinets and carpet flooring. Ultimately, if the tile floor was already hollow, the water that gained access due to issues related to an improper installation or improper maintenance may end up damaging the floor or adding damage to an already damaged floor. Either way, the flooring damage may end up being associated with a particular water event.

Secondary Causes

Secondary causes may apply to floors with concrete substrates as well as those with wood substrates, but just the fact that a wood substrate allows for more elements that may be affected by moisture would lead one to rightly assume that more things can go wrong when a tile floor over a wood sub-floor becomes wet. If tile flooring was installed up to wood materials such as baseboards and cabinetry, the tile floor may be subjected to the force of expanding wood in one or more locations, or around its perimeter. Wood wedges soaked with water were used by Egyptians to split solid rock; the force of expanding baseboards can most certainly exert a substantial amount of pressure on a tile floor. The shear force of expanding wood can easily break the bond between tile and substrate. Additionally, a wood sub-floor may expand due to elevated moisture levels, causing it to break loose from the mortar bond.

What About Microbes?

That’s a good question, and one of the main reasons that tile floors end up being removed; whether necessary or not. When a homeowner is told that water is trapped underneath tile flooring, the response is usually one of concern. That makes sense, but is there always a cause for concern?

Depends on What Underneath

Here in Southern California, many, if not most tile and natural stone floors are installed over concrete. The most common installation is a thin-set mortar installation (Tile Council of North America installation method F-113). A less common method uses a mortar bed to level out the substrate and help prevent cracks from transferring from the concrete through the tile. There are variations of these methods and both may incorporate a crack isolation membrane.

So the Question Is: What About Mold?

In order for mold or other microbes to live, there needs to be a food source. The Tile Council has published a helpful article on this subject called “The Down and Not-So-Dirty Truth
About Ceramic Tile and Microbes” by Jennifer Ariss (November/December 2009 www.TILEmagonline.com).

Basically; concrete, mortar, tile, stone and most crack membrane materials do not provide a hospitable environment for microbes. The ph of concrete is not in a range suitable for microbial growth (if there happened to be any organic material to be used as a food source), and assembly materials such as backer board, mortar and membrane materials must conform to ANSI and ASTM standards for fungal and bacterial resistance. There is the chance of an improper installation providing a means for microbes to live; for example, using asphalt felt paper as a crack isolation membrane. Under normal circumstances though, moisture trapped underneath ceramic tile or natural stone does not present a microbial risk.

What About Wood?

When a wood sub-floor is involved, it’s very difficult to determine with any certainty that there is no microbial risk. The fact is, in most cases non-destructive moisture testing can’t provide accurate enough data to conclude that no microbial risk is present, and when performing destructive testing, the absence of matching flooring material for repair may result in the need to replace the continuous floor. in such cases it may be best to cut through a lower level ceiling if available, or test from underneath a crawl space in order to probe the wood sub-floor for moisture testing. Even if such access is made available, test results may end up being inconclusive, since a visual inspection or hygienic testing for microbial growth may require damaging the floor to gain access to the area between the wood sub-floor and backer-board/mortar bed.

Contaminated Water?

Here’s where a lot of floors just end up being removed no matter what. It may seem best to just not chance it, and there are times that I would have to agree.

That does’t mean that it’s always necessary to remove flooring when it comes into contact with contaminated water. No one tears out their tile floor just because the toilet overflowed; that is, unless someone else is paying for it.

Same logic applies with contaminated water versus clean water; except it’s really important to know where contaminated water has spread to. If microbes are introduces into a void between ceramic tile and concrete, the microbes will eventually die due to lack of food. Now, it may be that enough contaminated water was introduced that drying becomes difficult. In these cases it may be appropriate to remove flooring based upon a recommendation from a water mitigation expert, although I believe that most often these recommendations are precautionary and not always necessary.

Contaminated water and wood sub-floor will probably require flooring removal unless there’s a way to gain access to the affected area for decontamination. With a wood sub-floor it’s just not possible to guarantee that no microbial issues exist. It may be, however, appropriate to consider trapped microbes as being “contained” and left as is.