Is there a method for moving a construction joint using anti-fracture membrane?


I have a small floor install in a basement. A construction joint runs about 1/3 into my floor. I’m installing 6”x36” porcelain tiles over this floor. My plan was to create a soft joint in line with the construction joint. 

Two problems exist with this joint. 

1. It’s out of square 3/4 to the adjacent walls. 

2. If I lay out with full tiles on both sides of where the construction joint is located, I end up with a 1” strip on one of the adjacent walls. 

I was under the impression there is a method for moving the joint using anti-fracture membranes, etc. Whatever the case, would you please advise me as to what would be the best practice based on the situation I described?


Thanks for your question. This is a common concern and I am glad you are addressing it before installing the tile.

Manufacturers of crack-isolation membranes will sometimes allow that one or more products are capable of spanning a construction joint in the substrate. This is a case-by-case, product-by-product, manufacturer-by-manufacturer consideration, since many products have similar properties but different limitations. I suggest you contact your go-to membrane manufacturer and ask which of their products might be suitable for this application and what their instructions are for applying it. Their Technical Data Sheet and Installation Instructions will be very informational.

IMPORTANT NOTE: Membranes designed for crack isolation are only appropriate for in-plane (lateral/side-to-side) movement. They are not appropriate for out-of-plane (up and down) movement of the substrate. If one or both of the sections of substrate that have been isolated from each other move up or down, the membrane likely won’t be able to protect the tile. Crack-isolation membranes have limitations for how much side-to-side movement they can handle. This varies from product to product.

In addition to EJ-171, the TCNA Handbook has two methods for crack isolation (Full Isolation and Partial Isolation). Please use the Method Locator in the back of the Handbook to find these methods. They will provide you with more information. 

– Mark Heinlein, NTCA Training Director

Lighting is causing wall-washing effect


I wonder if you can help me out on a problem we are having based on coved lighting that causes the wall-washing effect.

We have a project we did a year ago where we installed 3” x 6” wall tile at the restroom walls; at the wet walls there is coved lighting. When they turn on the lights, the installation looks horrible at the walls with the light cove. Do you have any information about light placement, and what is the allowable variance in the actual tile-to-tile installation, and also information how to resolve this besides tearing out the walls? Thank you! 


In Chapter 6 of the NTCA Reference Manual there is a section called Critical Lighting, as well as a Lighting and Tile Installations section in the TCNA Handbook for Ceramic, Glass and Stone Tile Installation. They both address this problem. There are also standards in both TCNA and ANSI about allowable lippage. For the tile and grout joint size you are using in this installation, the allowable lippage is 1/32″, which is about the thickness of a credit card.

The sections about lighting explain how installations that meet industry standards for lippage can look poorly under these lighting conditions. Some installers in the same situation will turn off the lights and put a different light source on at a different angle on the same wall. They then document both lighting situations with photos, showing this to their customers to explain the effect light can have on the appearance of the installation. I would check to make sure the installation is in tolerance for lippage. Then, I would take the NTCA Reference Manual and TCNA Handbook to your customer showing them what our industry says about this type of lighting. I hope this helps.

Robb Roderick, NTCA Technical Trainer

Do the typical TCNA standards for expansion joints pertain to GPTP too?


I wonder if I could get some advice from you for this project that we are to start installing in a few weeks. It is a medical office building in San Diego, using large-format porcelain tiles in the nominal size of 30” x 60” x 1/4” thick. The floor is a concrete slab that we are going to install using the thin-set method, and there are some control joints in the slab. We have roll-on liquid crack isolation and will be installing the tile with a crack-prevention mortar. 

My question for you is: Do the typical TCNA standards for expansion joints pertain? In reading literature from a different manufacturer on their thin porcelain slabs, they list 20’-0” o.c. for expansion. And how would you handle control joints in an installation where they will not fall on a grout joint and we are using a roll-on crack-isolation membrane? We have about 7,000 sq. ft. of this flooring.


The answer is yes. The ANSI Standards and TCNA Methods for expansion, movement, change in plane joints, honoring control and contraction joints etc., do pertain to that type of tile, which is known as Gauged Porcelain Tile/Panels/Slabs (GPTPS).

ANSI A108.19 is the installation standard/instructions for GPTPS. Section 18 of this standard refers to the ANSI A108 standard for expansion joints and TCNA Handbook Method EJ-171.

Requirements for placement of the joints, width of the joints and material used to fill the joints are detailed in the standards and in TCNA EJ-171. It is very important to understand that it is the job of the design professional or engineer to specify the placement and width of all joints in the design drawings and specifications. Their calculations for placement will include consideration for substrates subject to deflection, shrinkage, and expansion, etc.

I strongly encourage you to contact the tile manufacturer to ensure their tile is rated for a floor installation. Some GPTP manufacturers have different types and thicknesses of tile, some of which are recommended for wall installations only.

When using any crack-isolation membranes – and especially when using a liquid membrane – it is extremely important for you to:

Ensure the membrane is installed exactly as required by the membrane manufacturer’s instructions. This includes preparation of the substrate, number of coats to be applied, wet film thickness of each coat, cure time, etc.

Contact the membrane manufacturer and request from them the specific requirements for their membrane to bridge control joints. Ask them for a job specific warranty for this installation.

Have you attended a GPTP installation course? 

When to use moisture-resistant gyp-board or cement board


I’m writing with a question that I hope you can either answer or point me to the best resource that would be able to provide some insight.  

We’re doing architectural work for a national chain restaurant and I’d like to confirm that we’re using the appropriate backer board for tile walls. The question is: moisture-resistant gyp-board or cement board?

We use wall tile in food prep areas and restrooms. The walls get wiped down and might get splashed with water, but they don’t get hosed down or soaked.  

Let me know if there’s a simple rule when cement board should be used, as opposed to moisture-resistant gyp, or if there’s a reference standard that would shed some light on this question (I already tried the TCNA Handbook).


Thank you for contacting the National Tile Contractors Association. Industry-recognized wall tile installations are found in the TCNA Handbook

Two methods that use gypsum board are method W242 and W243. In the Environmental Exposure Classification section of each method it notes that they are appropriately used in Residential 1 or Commercial 1 type installations. Commercial 1 areas are described in the Environmental Exposure Classification of the TCNA Handbook as tile surfaces that will not be exposed to moisture except for cleaning and gives examples  such as: floors in areas with no direct access to the outdoors and no wet utility functions; hallways; dry area ceilings; soffits, decorative/accent walls; and corridor walls.

Commercial 2 is described as surfaces that are subject to moisture but do not get soaked or saturated due to system design or time exposure. Examples of Commercial 2 installations are: floors in bathrooms and locker rooms; some backsplashes and other walls such as bathroom walls and wainscot where water exposure is limited and or water is removed. Commercial 3 is described as areas that are soaked, saturated, or regularly and frequently subjected to moisture or liquids. It also lists some commercial kitchen walls.

Method W244 uses cement backer board in the installation and is suitable for Commercial 1,2, and 5 installation. 

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. 

Waterproof membrane for concrete substrate


I will be tiling a shower/bathroom house at a campground this summer. The floor substrate will be concrete and the walls will be masonry block. The architect did not specify any waterproof membrane for the entire job. I am wondering if this will be okay since it’s all concrete. Should I suggest some kind of waterproofing/crack-isolation membrane? If so, could you refer me to the place in the TCNA Handbook that explains this?


Thanks for contacting the NTCA. We encourage everyone to use industry-recognized methods found in the Tile Council of North America Handbook for Ceramic, Glass and Stone Tile Installation, and ANSI. There are a variety of shower methods that would work with the installation type you described (See methods B421 and B422 TCNA Handbook). All incorporate waterproofing that meets ANSI A118.10. standards. 

Having the appropriate slope and drain connection is crucial in every shower design. Water can pass through grout, stone and many tiles, so installations need waterproofing beneath the tile. Although the subsurface is block and concrete that may not be harmed by water, water can pass through these surfaces and get into areas where it is not desired. When waterproofing is not used and water soaks the block or concrete, those areas can continually remain wet, discoloring stone tiles and grout. A wet subsurface also creates a source of moisture that can encourage mold growth when organic materials like soaps are left behind. 

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

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