Repairing Saltillo tile


I got a call today from a customer who chipped her Saltillo tile and wants to know if it can be repaired. The tile actually has many chips and imperfections, but these particular chips took the outer glaze or sealer off of them, exposing the raw clay. Could I go over the open spots with a high-gloss sealer and close them up? Any ideas or guidance would be greatly appreciated.


Depending on the depth of the chip, the application of a high gloss sealer could work. One important component when using sealers over pre-sealed tile is to make sure that the sealers are compatible with each other. Whenever two sealers are not compatible, it can leave a white cloudy appearance on the tile that is difficult and sometimes impossible to remove. So always do a test area in an inconspicuous place like a closet or behind a refrigerator. If you can identify what was used originally to seal the floor, it would be ideal to use that product. Many times changing the color of the clay underbody that is visible in the chipped area by sealing makes the chip virtually disappear. I hope this helps. 

– Robb Roderick, NTCA Technical Trainer

How close to the tile wall can a linear drain be placed?


How close to the tile wall can a linear drain be placed?

I’m planning to use an elastomeric waterproofing membrane and install the mortar bed using the divot method around the drain.  Can the drain flange sit directly on the subfloor with mortar packed around it? I haven’t found a standard for thickness of the mortar bed around the drain flange.


Great question!

Many linear drains can be set right up to the wall so that the wall tile runs perpendicular down to the drain opening making a very clean look. Just need to make sure the drain top/grate is removable.

The type and manufacturer of the drain system you are installing will determine how close the drain body can be placed to the wall and how the waterproofing will be flashed to the drain body. As you know, it is critical to not have a cold joint or crack or debonded waterproofing connection from the wall to the drain body. If using a liquid, you might want to consider adding a scrim film to help with the bonding/connection. Please check with both the drain and liquid manufacturers to verify their instructions for the membrane connection in a close to wall configuration.

I am not familiar with every type of drain body out there but I do know there is at least one designed where the flange can be mounted fairly flush with the substrate. Best to check with the manufacturer of the drain body.

There are some bagged mud products that are designed to ramp down to aggregate level. I can’t vouch for their performance at such a thin layer at such a critical point as the transition to the drain in a shower floor. Are you using a bagged mud product? Does the manufacturer of the waterproofing membrane have one that will work well with their membrane system at such a thin layer?

If the manufacturers of the drain and setting materials are able to give you a written confirmation of their concurrence with this install you should be good to go. If not, I would reconsider and go with a different approach. Hope this helps! 

– Mark Heinlein, NTCA Training Director

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


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?


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

DCOF rating requirements for interior and exterior tile


I’m looking for a straightforward synopsis of DCOF rating requirements for interior and exterior tile. I’m finding a lot of long-winded articles, but nothing clear and concise, especially related to exterior. Do you know where I could find that?


I’m not aware of a simple formula for determining required DCOF for a given installation.

Tiles are tested to determine their Dynamic Coefficient of Friction using a machine that mimics the start/stop/pivot motion of a human step. The test is done with the tile lying flat and a slightly slippery liquid applied to its surface. The testing machine produces a decimal number, e.g. 0.42, that depicts the slip resistance of the tile under the prescribed test conditions.

A tile with a DCOF rating of 0.42 may work well in a given situation. Differing situations may require a different DCOF. For example, an exterior public pool deck that is pitched for drainage and is exposed to very wet conditions will likely need a tile with a higher DCOF than a private bath floor that is flat, has occasional use and gets slightly wet.

– Mark Heinlein, NTCA Training Director


For a straightforward overview of the DCOF, go to the 2019 edition of the TCNA Handbook on page 4. You should also review the ANSI A137.1 Specifications for Ceramic Tile section found on  pages 15-16 and section 9.6.1 found on pages 24-29.

As you review this standard, you will find this statement in part, “The standard now requires a minimum wet DCOF AcuTest value of 0.42 for ceramic tiles for level interior spaces expected to be walked upon when wet.”

The DCOF test is conducted using the BOT 3000, or an equivalent, to test individual non-installed tiles using a solution of SLS (Sodium-Lauryl Sulfate) in a 0.05% concentration with the BOT 3000 traveling 10” across the tested tile. Realize that the tested tile and tiles out of the box may and most times will have a different DCOF than an in-service installed tile. Factors such as environmental conditions immediately after a rain storm, melting snow, oil, grease, maintenance regimen and/or any other elements that reduce traction, create slippery conditions where the risk of a slip cannot be completely eliminated. 

The BOT 3000 is a device for measuring the dynamic coefficient of friction (DCOF) of ceramic tile and many other hard surface floorings.

To paraphrase the standard, the DCOF test only applies to interior level surfaces expected to be walked on when wet. It does not cover tiles installed on exterior applications, sloped surfaces, areas exhibiting poor drainage, or polished products. 

If needed or required, the services of a company utilizing the BOT 3000, or equivalent device, can be used to test an on-site tile installation to determine its DCOF. 

– Scott Carothers, Director of Certification and Training, Ceramic Tile Education Foundation


At least I know it wasn’t just me who couldn’t find information on the exterior standard. This information does help, and I’ll keep it to reference, but for my specific situation running a test wouldn’t work, timing-wise. 

It sounds like there’s a need for an exterior standard, but I’m guessing this hasn’t happened because conditions can vary so greatly. 

Stackable wall tile

stackable wall tile


We’ve been struggling with production when it come to installing “stackable” wall tile. I’ve been installing for 31 years and stackable wall tile used to be fairly simple. It seems that installers today are having more trouble than ever getting their footage numbers due to bad tile sizing. We’ve shown several samples to the factory reps, but the answer always seems to comes back as “yes, these tiles are actually within tolerance.” Go figure! I was wondering if you could possibly help me to determine how to gauge what is considered out of tolerance and how to pursue the manufacturer about this problem. Thanks for any and all insight. 


I’ve not heard this complaint very often, maybe because of the shift away from the use of stackable wall tile. The ANSI A137.1 standard for size difference seems to be a very liberal number allowing quite a bit of difference before the tile doesn’t meet standards. I do think there can be significant difference depending on the manufacturer of the material. If another manufacturer makes a similar material, there might be a better substitute.

Because stackable wall tile has a set grout joint size usually 1/16”, if the tile has very much deviation it may not meet minimum grout-joint size tolerances. The TCNA Handbook says the minimum grout joint should be three times the facial deviation of the tile themselves. The example they give is for tiles that deviate 1/16”, you should not have grout joint smaller than 3/16”. You could create a larger grout joint to hide some of these size differences, but those changes would have to be approved by the end user. Also, the fact that the tile is stackable is desirable to some installers because installations can be done quicker. I think speed was a major issue to begin with.

Looking for a substitute, or changing the grout joint size, are the only things that come to mind. 

– Robb Roderick, NTCA Technical Trainer

Testing might help, but just to note, TCNA will only measure and report the tiles supplied. They won’t assess whether the tolerances actually apply in a given scenario or look at any other nuances that could be relevant, for example whether there is a spec requiring the tile to meet A137.1, or if the manufacturer claims conformance to it. There are enough instances where these things are not the case. Testing costs money, and there is not much reason to have it done if meeting the standard isn’t somehow expressly required in the first place. When conformance to A137.1 *is* required, there are also sampling and lot acceptance criteria in the standard that allow for some of the tile to be outside the tolerances. It’s not a huge amount, but just mentioning it.

I agree with Robb’s suggestions on looking for a substitute or changing the grout-joint size. But I’d want to know more before making changes, just to be surer about the root cause. For me, that would influence whether the additional cost of improving the look is something that could/should be charged for.

I’d be really interested in knowing more about these tiles or getting a box. If they truly meet standards but are taking significantly more effort labor-wise, and this is happening more and more, that would be something to possibly try to address in the standards arena. It could be a PSA for contractors, or for GCs, given to them by contractors. 

– Stephanie Samulski, NTCA Technical Director

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


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?


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

What fill should we use to withstand the weight of an 800 lb. clawfoot tub?


We have a customer that has terrazzo in their home. We removed the tub surround and a closet area and there was no terrazzo underneath it, so it is at least a 1-1/2″ drop down that we need to fill before installing floor tile on top. We will be installing a very heavy claw tub on top of the floor tile. What do you suggest we fill the hole with that can withstand the weight of the tub that is at least 800 lbs.? Concrete would have to cure and my customer is not willing to wait the 30 or 60 days unless it is the only solution. Is there anything else we can use?


I suggest that a thick bed (mud bed/dry pack) would be the best alternative to fill the void. Most require a 72-hour cure time at the longest. Some pre-mixed versions can be tiled over (or have membranes applied) sooner. If using a wet-bed method, it is tiled immediately.

Details for installing a thick-bed method can be found in the TCNA Handbook. Use the Method Locator for Ceramic Tile near the back of the book to locate the Floor methods then find the type of substructure (i.e. wood framing), and you will be directed to the page number(s) for the appropriate methods. 

What is the best product to use to install resin-backed stone?


What is the best product to use to install resin-backed stone?


Epoxy is the safest choice. You could do a bond test with thinset to see how well it will adhere. Simply install a piece over concrete or concrete board, allow it to dry, and then see how well it is stuck. Some mortar manufacturers are making mortars they claim will adhere to resin-backed stone. If you have a relationship with a representative or a mortar manufacturer, they may have something they will warranty with it. Contacting the stone provider is always your first course of action. If you don’t get answers or test it, use epoxy. 

How to remove stains from pavers


I have a client with peacock pavers. They had a large mat in front of their door with two planters on either side if it. The planters leaked onto the mat and drained off the porch, but the dye from the mat has left a bad stain on the pavers. Any recommendations on how to pull those stains out?


2019-20 NTCA Reference Manual

I would contact a company that makes sealers, grouts, and related products and ask them if they have a product that will work to dissolve the minerals that leached in from the planters. Some setting material manufacturers also make products like these. If you know which company made the grout and/or thin-set, they would be the logical choice to ask first.

Do you have a copy of the NTCA Reference Manual? In the manual, there is a section dedicated to processes to remove stains from tile and stone. A quick browse through the table of contents will point you to this section that will provide tips and tricks that may help remove stains like these.

– Mark Heinlein,
NTCA Technical Director

Is the drywall installer or tile installer responsible for the joints/corners?


We have a project with wall tiles that are 4” x 40”, 8” hex and large 24” x 47-1/8”. The general contractor has drywall figured and states that joints or corners shouldn’t have to be mudded/done by the drywall installer nor primed! Our tile installer said that he wants the joints and corners completed and everything primed before he will install. These areas are not in a wet area. However, the large tile is at a fireplace wall.

What is correct?


TCNA Handbook Methods (l.) W242 and (r.) W243.

There are two recognized methods for installation of tile over gypsum board found in the Tile Council of North America Handbook. They are methods W243 (thin-set) and W242 (organic adhesive). Both have a section of the method that are titled “Preparation by Other Trades”. In that section it states gypsum board shall be installed per GA 216 “treated with tape and joint compound, bedding coat only (no finish coats). Nail heads one coat only.”

To my understanding primer is not needed. We do recommend slightly dampening the surface of the drywall to help ensure the board does not prematurely draw the moisture out of the thin-set bond coat.

– Robb Roderick,
NTCA Technical Trainer


Q: Would you say primer is the responsibility of the tile installer or drywall installer?

A: If we are going to put tile onto the drywall surface and the primer is necessary to prepare the drywall for a successful tile installation, this would be the responsibility of the tile contractor and not the drywall contractor.

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