Most of our home inspections completed by Bay Area Mold Pros include an attempt to determine if moisture is present behind bathroom wall tile. Moisture often makes its way past wall tile, often through the space between the tile when grout is missing, or when the grout was improperly applied, or was never properly sealed. Homeowners are often surprised to learn that conventional grouts aren’t really waterproof, unless they have had a proper grout sealer applied, and re-applied when necessary.
Once water has made its way past the tile, it contacts whatever tile “substrate” was used. For decades, this substrate was made of mortar, and was “floated” onto the wall, generally onto chicken wire that had been nailed with spacers over some type of building paper. In the San Francisco Bay Area, this building paper was often the same “tar paper” used for roofing, and was also “asphalt-impregnated building paper” that was often used under exterior siding and stucco. These mortar substrates often lasted for decades, and indeed, many still survive throughout the area. Our family home in San Francisco, built in 1936, still has its original Art Deco bathroom wall tile in both the shower and above the bathtub. All of this tile was installed over a mortar substrate.
But mortar substrates require a certain skill level to apply them properly, and many modern tilers prefer to install tile over other simpler (and less costly) substrates, such as cement board and Hardi-board. When properly installed and waterproofed, these newer substrates will last for years, and although not as stable as mortar, they are very stable. But starting in the 1950’s, many builders started using standard drywall as a tile substrate, and over the ensuing years, these tile jobs have mostly failed. My wife and I purchased a home in the San Francisco Bay Area in 1980, and the shower tile was so “mushy” near the shower pan that you could move it by simply pushing on it with your finger. I gutted the bathroom and determined that the tile had been applied directly over 1/2″ drywall, which was completely saturated with water was falling apart.
I replaced the original 1/2″ drywall with a product that was fairly new in 1980, “green-rock.” This 1/2″ drywall was faced with green (rather than white) paper, and did not have the standard gypsum contents present in standard drywall. At the time, lumber yards and the newly introduced “big box” stores were selling this green rock as “waterproof drywall.” You can see where this story is headed, within a few years, this green rock had failed, and the shower needed to be gutted again. Several years went by and green rock was replaced by “purple rock,” which was again touted as waterproof drywall. But neither purple rock nor its predecessor, green rock, were ever meant as tile substrates, and should only be used as backing behind a properly installed tile substrate.
The wall tile depicted in the photo above was present in a home that I inspected last week in the San Francisco Bay Area. The lowest courses of the wall tile were loose, and when I pushed on one of the tiles, it simply fell off the wall, revealing what I suspected was behind it, standard drywall. Once water has made its way past the wall tile and comes into contact with the drywall, the drywall will suck up the water like a sponge, and will then fail. Mold loves paper, and because drywall has a paper face on both its front and back side, it makes a perfect host for mold growth. So when drywall tile substrates fail, it is very common for mold growth to occur.
So the lesson here is straightforward, never allow wall tile to be applied to any type of drywall in a water-setting, which includes shower enclosures and the walls above bathtubs. These installations require proper tile substrates and proper waterproofing. They also require appropriate sealing of the grout, and proper maintenance, which may include re-application of the grout sealer. And if the tile surface is properly maintained, it can last for many years. The tile in our family home is now 84 years old…and is still going strong!
The majority of my mold inspections take place in San Francisco, where most of the neighborhoods were built many decades ago. Starting around the 1920’s, the tiled stall shower became very common in homes and apartments throughout San Francisco, and surprisingly, many of those showers still have their original tiled walls!
Bathrooms are often the first room that I visit on my inspections, both because this is where homeowners often see visible mold, and because this is where my meters often detect moisture problems. The shower depicted in the above photo is actually fairly common in terms of the problems it presents.
The tile is cracked and broken, the grout is missing in places, and mold is visible on both the cracks and the grout. These showers were all built with “custom shower pans,” meaning that the pans built on site, where mosaic tile was installed on a mortar substrate. Under the mortar it was common to “hot-mop” the area (essentially install a hot tar roof). After these shower pans were hot-mopped, both the walls and the pan then received a layer of mortar substrate. This mortar was typically floated over chicken-wire, which was stapled or nailed to some type of building paper.
These tiled showers have lasted for decades, but in almost all cases, the grout joints have failed and water has made its way past the tile and into the mortar substrate. At Bay Area Mold Pros, we use a variety of meters to detect this moisture, including thermal imagers. One of the problems within the mold inspection industry is interpreting just what this moisture means, in other words, we know we have moisture, but has this resulted in mold growth?
The best way to answer this question is through the use of air samples. Although some amount of surface mold is often visible on the grout joints of these old showers, it is oftentimes just that…surface mold. In other words, the moisture that has made its way past the tile may not (yet) be resulting in mold growth that is making its way into the air. That’s where air samples become so important.
Air samples provide a snapshot of the air that’s present in a particular place at a particular time. The cassettes used to collect these samples contain a lab slide. The mold spores attach to the slide, and the lab techs then place these slides under high powered microspores and analyze them. These techs will break out the mold spores present both by number (mold spores per cubic meter is the industry standard), and by mold type. Even though people within the industry often refer to the “species” of mold collected in air samples, the lab actually breaks the mold spores down to the “genus” level, which is more than adequate for the purposes of identifying the severity of a mold growth problem.
The bottom line…these showers need to go! After 50, 60, 70, or even 100 years, the shower has outlived its usefulness, and it’s time to replace it. Many homeowners opt to have seamless panels installed to replace the old tiles walls, thus avoiding the problems associated with grout.
For those who choose to have new tile installed, it’s crucial to have the grout “sealed” after installation, in order to address the issue of water making its way past the grout. Properly installed tile and grout will provide years of service for homeowners, thus avoiding the need to have Bay Area Mold Pros visit your home again.