Ceramic Industry Blog

Guest Blog: Tile Tech Notes

August 11, 2010
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Nitty Gritty Details

OK class, get out your American National Standard Specifications for Ceramic Tile books and turn to page 13. Now, who would like to tell us about the Diagonal Warpage specifications for Rectified Porcelain? Anyone? Hello? Bueller?

As the Technical Services Director for Florida Tile, I get to answer the door when someone comes calling with a complaint. By the time someone complains, the battle is largely lost because it means that what they were expecting wasn’t what they received. The ANSI specifications for tile set minimum levels of what consumers should expect when they buy tile. Unfortunately, most people don’t know that the standards exist until after they’ve come back from vacation and seen what’s been installed.

Tile standards are written by the tile industry and, as such, are a reflection of what our equipment is capable of producing. We could make every piece perfectly flat and exactly the same size, but then the tile would cost $50,000 a foot and we would soon go out of business. Instead, we make a lot of tile to keep the costs low and we set very tight tolerances while communicating up front that there are going to be some differences from piece to piece.

So what are those differences? The answers can be found in the ANSI specs. I won’t begin to try to explain every single attribute of tile (your homework is to pick up your copy and leaf through it). I will touch on the biggies, though, because whether you buy, sell or make tile, it’s important to know what is in the specs.

First, tile is fired in a kiln so it is going to vary in size. Sometimes, we grind the edges (rectified tile) so it is very consistent from piece to piece and consumers can use those little, itty-bitty grout joints that seem to be so popular. Of course, that costs more and even rectified tiles, according to the specs, can vary in size by up to ± 0.8 mm. If you don’t want to pay extra to have your tile rectified, be forewarned that it may have up to ± 2 mm of size variation (around 1/8 in.). We usually do better than that, but we only guarantee that our tile will conform to this spec.

Next, and again because tile is fired in a kiln, it’s not going to be perfectly flat. In fact, we put a little bit of “positive bow” in it on purpose so the corners won’t stick up. Again, the details are there in the specs but tile may have up to 2 mm of positive (middle higher than edges) or negative (edges higher than middle) warpage. What does this mean for the consumer? Usually nothing: if tiles are installed uniformly, the eye won’t pick up the difference. However, if tiles are installed with the edge of one tile next to the middle of the next one (commonly referred to as a brick pattern), some lippage will become evident.

The specs I have been quoting are for pressed porcelain floor tile, which is the most common tile product but by no means the only one. Other tiles (mosaic, quarry tile, glazed wall, etc.) have their own unique tolerances. The most current version of the specs is ANSI A137.1-2008, which was published in 2008. The specifications are constantly being updated, so make sure you are using the latest version.

Now, your homework is to write a 500-word essay on the ANSI specs for tile. Hello? Anyone? Bueller?


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Very thorough

Nabih Saba
August 13, 2010
Fantastic professor Dan.... well explained and said

rectified porcelain

September 28, 2010
Does all rectified porcelain need to be installed over a "mud" bed,or does it depend on groutjoint width and existing floor conditions?


Dan Marvin
September 28, 2010
Rectified tile does not require a mud bed. In fact, most installations these days are done with thin-set. As long as your subfloor meets the requirements spelled out in the Handbook for Ceramic Tile Installation, you should be good to go. I would highly recommend against a 'brick pattern' though where the tiles are staggered 50%. This puts the highest point of one tile (the middle) next to the lowest point of the next (the corner). A 33% offset is usually the max, and opening up the grout joint helps as well.



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