Ask the Experts – July 2016

SponsoredbyLaticreteQUESTION

I am trying to find out if tile can be installed over tile. I have a ranch house in Florida built in the late ’70s with an original slab floor and terrazzo. Ten or so years ago the then-owner installed 12” x 12” tiles over the terrazzo. We want a new tile floor but do not want to remove the current tile. I know it’s “all about that base,” and our current tile floors are solid as a ROCK, level, not a single hollow or loose spot anywhere. As a matter of fact, it is almost impossible to get this tile off! No contractor will lay tile over tile, but I have read many, many articles online – from contractors – that say it can be done. What do you say? Thank you!!!

ANSWER

Thank you for contacting the National Tile Contractors Association.

Cementitious terrazzo is really just a type of mortar bed that has been ground very smooth. The only problem with going over it is the terrazzo is usually highly finished or waxed, with multiple layers. This finish must be completely removed and the terrazzo re-ground to open up its pores before tile installation. When properly prepared with the right materials, it becomes an excellent substrate for a new tile surface.

A qualified tile contractor is the best person to determine whether your existing tile installation is well bonded to the terrazzo.

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Twin City Tile Co. Ltd., of Kitchener, Ontario, was responsible for restoring the Registry Office of the Waterloo Region, which was constructed in 1938 and designated as a Heritage Landmark by the Historical Society. This included the original terrazzo floors, many of which consisted of nine cement colors and eight different colors of terrazzo chips of various sizes, with intricate geometric patterns and three different thicknesses of zinc and solid brass strips. Although you wouldn’t want to tile over a terrazzo floor of this quality and beauty, terrazzo CAN be an excellent substrate for tile, given the proper preparation by a qualified tile contractor.

Tile-over-tile is a method in the Tile Council of North America’s TCNA Handbook for Ceramic, Glass and Stone Tile Installation, providing the bottom layer of tile is well bonded and properly prepared to accept the bonding materials for the new layer of tile. This can be done by scarifying or grinding the surface of the existing tile and/or by applying an appropriate primer that will allow the new setting material to achieve a proper bond. Grinding the surface of existing tile can create a lot of dust and may release potentially hazardous particles into the air from the materials used in the glaze. It is best to have this work performed by a certified, experienced professional installer. Such an installer will also be familiar with the primers and setting materials that will work best for this type of installation.

A well-experienced, qualified, certified tile installer/contractor will know and understand the methods detailed in the TCNA Handbook and will be able to examine your existing installation and determine the best approach for the new tile. Look for a contractor who is a CTEF Certified Tile Installer and a member of the National Tile Contractors Association. I have included links below to help you find one near you. A contractor who is a member of the NTCA has a direct connection to us for any technical advice and support if needed.

If this is an above-ground construction or on a wood frame subfloor, consideration must be made to support the weight of the new tile installation. A qualified tile contractor can assist with this, but an additional contractor or engineering assessment may be required. Floor-height transitions to other areas must also be considered. The contractor you eventually hire should discuss this with you.

To locate an NTCA member contractor: http://www.tile-assn.com/search/custom.asp?id=2759

To locate a Certified Tile Installer: https://www.ceramictilefoundation.org/find-certified-tile-installers

I hope this helps!

Mark Heinlein
NTCA Technical Trainer/Presenter