How to Install Onyx Tile

Tips on Installing Onyx Tile Properly

By Mark J. Donovan

Onyx tile is just simply gorgeous to look at. With its bright and varied translucent colors Onyx tile just screams elegance and character. Onyx tile looks great in any room, however it shines above all other tiles types in bathrooms. Installing onyx tile can be done by the do it yourself homeowner, however it does have its unique issues that you need to be aware of up front.

First and foremost onyx tile is translucent. As a result it is imperative to use a white thinset mortar when installing onyx tile. Otherwise, you’ll end up seeing the thinset mortar through the tile.

Second, onyx tile is brittle and as a result it needs to be fastened to a solid surface.

A cement backer board should be used on walls and floors when installing onyx tile. Use 5/8 inch thick cement backer board on floors and ¼ inch thick backer board on walls. Make sure after fastening the cement backer board to the floors and walls with non-corrosive screws that you tape and mud the seams with alkaline resistant tape and thinset mortar. Use a 4 to 6 inch wide taping knife to tape and mud the seams.

As for the actual installation of onyx tiles start in the center of the wall or floor surface area and work your way outwards. Prior to actually setting tiles, however, make sure to first mark some orthogonal reference lines on the wall or floor to ensure that the onyx tiles are installed plumb and square. Use a chalk line or level, along with a tape measure and pencil, to make the marks on the floor and/or walls. I prefer to make orthogonal marks every 12 to 16 inches along the surface of the area to be tiled.

Use a notched trowel to apply the white thinset mortar to the backer board. Then use your trowel to back butter each tile prior to setting the tile in the thinset mortar bed.


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Back buttering is essential when installing onyx tile since the backside of onyx tiles are porous. Back buttering ensures a solid bond between the tiles and the thinset mortar bed.

Do not use a manual score and snap tile cutter to cut onyx tiles. Instead use a tile wet saw to cut onyx tiles. Due to the natural crystalline formation of onyx tile a score and snap tile cutter will lead to significant tile waste, which is both expensive and frustrating.

After the onyx tile has set up, and before you apply grout, seal the onyx tile surface with a tile sealer. Onyx tile is very porous and the last thing you want to do is push grout into the surface of the onyx tile. It will be virtually impossible to remove later on.

Grouting onyx tile is done the same way as grouting any other type of tile. Mix the grout up in a bucket per the grout manufacturer’s directions. Then use a rubber float and work the grout into the tile seams at a 45 degree angle. 

How to install onyx tile

After every 9 to 12 square feet of tile area has been grouted use a clean moist sponge to wipe off the excess grout. Keep a clean bucket of water nearby so that you can rinse the sponge frequently.

After completing the entire grout job, go back and sponge down the onyx tiles a couple of more times using a fresh bucket of water each time. Wait 15 to 30 minutes between cleanings. Then use cheese cloth to polish the tile to get a clean and sparkling surface.

Finally, after the grout has fully dried, apply another coat of tile sealer to the entire tiled surface, including the grout lines.

For information on installing a shower pan membrane liner for a ceramic tile shower, see the Shower Pan Membrane Liner Installation Ebook from  The Shower Pan Membrane Liner EBook will quickly teach you the step-by-step process for installing the shower pan membrane liner correctly. It includes instructions on framing the shower stall, pouring the pre-slope and shower base mortar, and installing the shower pan membrane liner.

See’s Ceramic Tile Calculator

See my “How to Tile a Custom Ceramic Tile Shower” Ebook to learn how to tile your own shower:  For a detailed set of instructions on tiling a shower floor and walls, including pictures for every step in the process, see my “How to Tile Custom Ceramic Tile Shower Ebook”.

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