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Can we install over the sheetrock using a bonding primer or would it be better to install over a cement backer?

QUESTION

We are about to install 16” x 16” terrazzo cement tile (2cm) on a 10′ x 10 wall in a doctor’s office. The wall is a painted sheetrock. Can we install over the sheetrock using a bonding primer or would it be better to install over a cement backer?

ANSWER

The NTCA Reference Manual lists paint as a questionable substrate.

It may likely be better to install over a substrate that does not have paint beneath the bond coat where the bond of the paint to the substrate must be relied on to support the installation.

Some manufacturers have mortars or primer/mortar combinations that will bond to a variety of questionable substrates including paint. Consult your tile and primer manufacturer for their recommendation for adhering this particular tile to the substrate. 

Also be certain to check with the tile manufacturer to understand the required minimum deflection criteria for this type of tile. It will be at least L/360 or higher. 

– Mark Heinlein, NTCA Training Director

Is installing tile over sheet vinyl goods still a “questionable substrate”?

QUESTION

Can you please tell me where to locate in the 2019 TCNA Handbook information to determine if installing tile over sheet vinyl goods is still a “questionable substrate”? I do not see any ANSI specs that reference installing tile over glue-down sheet vinyl as an option. Is there a spec for this?

ANSWERS

There is not an ANSI specification or a TCNA Handbook method or detail for installing tile over sheet vinyl goods. The NTCA Reference Manual lists sheet vinyl as a questionable substrate. 

However, many manufacturers produce mortars that may be used to install tile over sheet vinyl provided it is fully adhered (not simply edge glued) and non-cushioned. Should you choose to do this, it is critical to follow the mortar manufacturer’s instructions.

It is vital that that you use an appropriate cleaner to remove all wax and surface contaminants from the vinyl. I recommend you do not sand or abrade the surface of the vinyl as some products may contain asbestos. 

– Mark Heinlein, NTCA Training Director


The list of questionable substrates is found in the 2019-2020 NTCA Reference Manual on page 31. They are not listed in the TCNA Handbook. There is, however, a method for renovations in the Handbook on page 288, Method TR711. It states “Ideally, existing finishes should be completely removed so the tile work can be placed on the substructure. This isn’t always practical, and as previously stated, some mortar manufacturers will warranty installations over vinyl flooring, provided they meet certain criteria.” TR711 goes on to give general guidelines for renovations. 

– Rodd Roderick, NTCA Technical Trainer