About the House: Tiling and Tapping Ain’t for the Timid

By Matt Cantor
Wednesday November 25, 2009 - 09:06:00 AM

Hindsight is, indeed, 20/20. Ah, that I knew then what I know now. Oh well. That’s just the way things are. Nonetheless, it’s embarrassing when you’re supposed to know all about a subject and, in reality, you’ve made plenty of the same mistakes that everyone else has made. 

Well, they say you should shoot the Buddha if you meet him on the road (which seems a little over the top to me; can’t I just shove him or maybe ignore him altogether?). In any event, I don’t tend to believe those experts who haven’t made mistakes themselves (or claim such), and I also have to wonder how much they actually know. So let me walk this dog proudly as my entry point to a very useful subject. 

When I remodeled my house in 1986 I was still young and there was a lot about construction that was fairly new to me. Tile installation (ceramic tile) was one of these things. I had a good feel for how to work with materials, but there are things you just won’t get in the beginning. You either have to make a bunch of mistakes or get really good guidance from those who have already made those mistakes. A combination of the two, along with quite a bit of reading, makes for what I consider a good education in construction. I’m not sure what they do in the classrooms, but I’m fairly certain that without some real-world experience (read: screwing up a bunch of times), you just won’t get there. 

We had decided to install ceramic tile on our counters and all around our sink area. We went to Import Tile in Berkeley where we met the amazing Tom Langlois. He’s still there and he’s still someone you want to meet; wonderful guy, Tom. We picked out, tile including what is called a V-cap. This was a piece that went over the front edge of the tile, covered the front of the plywood substrate and provided a small rise to hold water back from rolling off the edge. We ran them all the way around the front edges, including right across the front edge of the flush cast-iron sink. It looked really nice and we were, initially, quite happy with our choices. There were at least three different tiles that we worked with and they formed a fun pattern. For that, I have no regrets. What I didn’t know (nor, apparently, did my tiler, who now, believe it or not, works as a psychic—ah, Berkeley!) was that without a sufficiently well-sealed wooden substrate, and without enough of a cementitous backing, these angled tiles that capped over the front edge would, over time, get pushed outward to the front, just enough to snap them in two. 

What was happening was that moisture was getting though the grout (which is common, as grout is inherently porous, though it can be sealed to some extent by use of a liquid silicone sealer) and was saturating and swelling the plywood substrate below the tile. The swelling applied a force in both the upward and forward directions, thus snapping the angled tile at its crux. It took me some time to figure out precisely what was going on and I actually replaced a whole bunch of these once, only to find that they would, over time, suffer the same sad fate. Eventually, it was clear that the entire tiled counter had to go, in order to properly and semi-permanently (nothing is permanent, right?) repair the problem. 

This time, my friend, the amazing Tim Volz of Precision Tile in Berkeley, did the heavy lifting, replacing the plywood and installing a moisture barrier and a “mortar bed.” We did the tiling ourselves once the more complex part was done, and it’s been serving us well for years. Problem solved. 

I see a lot of failing tile installations and quite a few have some relationship to my personal tale of woe. But there are actually a number of different types of failures that I’m apt to see. Understanding these can help you to see them when you’re looking at a new house (or your current one) and to have some idea of what you’ll want to look for when a tiler is working for you. 

One of the things I do when examining tile installations is tap. No, not with those cool shoes— they’re way down in the bottom of the closet—but with my knuckles. Tapping and listening will show you (and teach you) a lot about a tile installation. When tile is properly installed, it will have good adhesion with the substrate (backing). This is achieved by the uniform distribution of the adhesive mortar (generally “thinset” mortar, which, as the name indicates, only needs a very thin layer to create a strong bond) on the substrate and good contact with both the substrate and the tile. If the mortar is the right consistency and properly spread over the backing material, it will grip a high percentage of the back of the tile. Tile installation guidelines call for specific percentages of contact area but it’s sufficient to say that something close to 90 percent is desirable. Poor installations can have contact area of well under 50 percent and these are much more apt to detach over time. They also allow water to flow behind the tile to a great extent, thus increasing the likelihood that the substrates will get wet and swell. You remember what happens when we get swelling, right? 

When you tap on tiles, you can hear whether or not they are well attached. If they’re barely hanging on, they will have a highly discernible hollow sound, as though there is a space behind them (which there is). If you do this tapping on enough tiles on a floor, counter or shower enclosure, it will generally be very clear whether there is a difference in adherence in the various tiles. A shower is a great place to do this test. It is quite common for tiles to loosen near the valves and tub spout over time and when you tap on these versus those at the other end of the tub, it’s often quite noticeable. That said, if you have a good installation, and this may be 50 years old (many of the old ones are still in great shape, though they may be somewhat cracked or chipped) you won’t hear a difference in the sound. 

So the take-home message to this portion of our penny analysis is that proper selection and proper distribution of the adhesive mortar is key, and failure to do this is one of the most common ways in which tile installations fail. By the way, I have found entire kitchen floors that were loose through this method, so don’t trust your eyes, trust your ears. 

It is very common for me to see floors where there seems to be a pattern of cracking running through the floor and, occasionally, I’ll even see floors where individual tiles seem to have been crushed under the footfall of normal daily activity. What’s important to understand is that tiles are brittle and of limited strength. If there are voids behind the tile and if people apply pressure to those voids, they are going to crack or crush those tiles. Now tiles do vary in strength and floors should be tiled using “flooring” tiles (OK, you can say duh, if you want, but this is new to many and nothing is obvious). I’ve seen many a floor installed using cheap low-strength tiles from big-box stores and many of these were cracked, chipped or crushed after only months of wear. Flooring tiles are more like stoneware then like china, having been fashioned from higher strength clays and fired at higher temperature. Still, this is not the main event.  

The big message is that tiles need to be uniformly supported from below, and this means several things. It means good adhesion, as we mentioned above; uniform distribution of adhesive so that we have no fulcrums on which to bend and break the tile; and a solid, relatively rigid base. This last part is critical and often overlooked. Tile doesn’t bend (at least not much), and when you try to bend it, it cracks. So the floor (floors are where we tend to get into the most trouble) needs to be made less flexible than it would normally be for a tile installation. 

Making a floor rigid can look something like the following procedure. However, your results may vary, as they say in the ads. Start with your old vinyl floor. Remove all the layers that take you down to the wooden “subflooring” (around here, that will often be a tongue-and-groove 1x4 fir flooring). Watch out for asbestos materials in the old flooring. This is most commonly seen in 9-inch square linoleum tiles. Once you have gotten to your wooden subflooring (this may also be plywood, oriented-strand-board or just about anything) you need to decide if the finished level of tile will end up being too high.  

A really good installer may choose to remove the subfloor, trim the top of joists (an engineer may need to be consulted if you’re removing more than just a bit) and then install a thick rigid plywood, using moisture-resistant screws and glue so that the end effect is a floor with less bounce. Also, you will then want to have enough height allowance left to install either a concrete tile-backer board or, better, a dry-pack mortar bed installed by a skilled professional like Tim.  

This last part requires tremendous experience and is not for the beginner. This process can square up rooms and level floors in such as way that the grid of tile that follows will not shine a beacon on the deformities of the room or slope of the floor. The mortar bed can vary in thickness on the walls or floors so that we end up with an easier tile installation and a better look. Tile backer board and dry-pack should both be installed over a moisture barrier. Anything that can be done, including sealing plywood, should also be considered. Today, we have a range of bituminous (tarry) flashing materials that do a fabulous job of sealing wooden substrates. We also have a range of liquid-applied ones and they, too, can provide a genuine edge against failure. When showers are being done, the belt and suspenders method may warrant a wetsuit and a whole range of polymeric sheet-goods are available. Shower pans generally want a Chloroloy membrane below the mortar (or something similar) since the level of attack by water is much higher. In a steam shower, I’d be tempted to use Chloroloy top to bottom although membranes like Chloroloy are generally only used at the bottom. 

I’ve said a lot and there’s a lot more than could be said but suffice it to say that when the gardener says that he or she can do tiling too, you might want to think twice. There’s a lot that can go wrong…and I haven’t even shown up with my tap shoes. 



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