What is the White Material on the backs of Ceramic Porcelain Tiles?

QUESTION

Simple question, for my general edification. Uninstalled tile, I always see a white residue, generally on the backing grid. What is this stuff? I can send a photo if you like as my description is woefully lacking.

ANSWER

ANSWER - The white material on the back of the tile is called engobe.  It is a ceramic pasted that is applied to the back of the tile for the firing process so the tiles do not stick on the kiln rollers.  On most porcelain tiles it is tightly adhered to the back of the tile.  On some tiles if it can wipe off when you rub your hand against it; in this case it can act as a contaminate and be a bond breaker, so the installers are supposed to clean the backs of the tile prior to installing all tiles to remove any contaminates.

6 thoughts on “What is the White Material on the backs of Ceramic Porcelain Tiles?

  1. Will says:

    I have a small gas space heater on a wall-to-wall rug and my gas company recently changed its policy and now says this is unsafe. They said if I put a “piece of tile” underneath the heater it will be considered safe by them. So I bought a piece of ceramic tile with a colorful decoration on it and decided to put it under the heater, design side down, in case the design is susceptible to heat. But on the back of the tile there are two “painted” white stripes that, from your description, I’m guessing are engobe. (I tried to scrub them off with Ajax but this had no effect.) Suggestions?

    • Donato Pompo says:

      Yes, the white stripes are likely engobe a ceramic material. Sometimes it is tenaciously bonded to the back of the tile and not removable. So there should not be a problem with leaving it. Regarding the front decorative side it should not be affected by heat since most ceramic tiles are made by being heated in a kiln at 1200 degrees F or higher.

  2. Dylan says:

    I recently installed a tile floor and some of tiles have White marks from the engobe on the face of the tile. My supplier had many of the boxes stored outdoors and some of the boxes were wet, so I’m assuming that’s the cause. How do I remove this from the surface of the tile? It’s not coming off with a simple sponge.

    • Donato Pompo says:

      White engobe is a ceramic based material. It normally will not adhere to the face of the tile if stacked on top of each other. If in fact it is a residual of the engobe, I would first use water and a 3 m type scrub pad and see if it will come off. If that doesn’t work then try using a detergent with the scrub pad in case it isn’t the engobe. If that doesn’t do it, then with care use a razor blade to carefully scrape it off without scratching the tile.

  3. Laura S. says:

    I have the same problem and I have tried clorox, paint thinner, acetone, acid, paint stripper, lacquer thinner and ajax. Most of the above using steel wool. After doing all of the above on one, it improved slightly, but there is still the obvious discoloration when viewed in the light. The only thing that seems to improve it is when it is wet. Suggestions?

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