Why do manufacturers require a 33% offset brick pattern?

QUESTION

Greetings! I was wondering if you could solve a mystery for me. On numerous jobs, for both walls and floors, we are asked by interior designers to install 12 x 24 or similar tiles in a standard brick aka 50% offset pattern. However, for many of these, printed on the box of tile or stated on the order sheet by the distributor, it clearly states in one way or another, “Brick joint pattern to be offset 33%.” When we point this out, the designer doesn’t care and won’t approve a mockup (because they don’t want to order any extra tile). Most of the time the 50% offset on the floor doesn’t end up becoming a lippage or shadowing problem, though we also use a leveling system so perhaps that helps mitigate it. On walls, however, especially depending on the lighting, it can be a real problem.

I would like to know why manufacturers recommend this if it often isn’t followed (I see plenty of tile jobs installed with the 50% offset)? And why do most of the distributors display the tile on a display board with 50% offset if the manufacturer requests a 33% offset? Is everyone just trying to cover their butts on potential lippage and/or shadowing issues? And since tile setters are “the experts,” not designers or customers, is a mockup the only true way to relieve yourself of culpability if shadowing and lippage do result from disregarding a manufacturer’s recommendations?

ANSWER

Thanks for getting in touch and thanks for asking an excellent question.

At Coverings ’19, NTCA Training Director Mark Heinlein presented a demo about wall wash lighting and lippage, citing information from the ANSI standard, as two teams installed wall tile.

It is my guess that the designers you are working with may not be familiar with the requirements of tile industry standards and the reason why those standards exist and why manufacturers require certain offsets for tiles they produce.

Listed below are the tile industry installation standards that relate to this discussion:

  • ANSI A108.02 section 4.3.7 – Lippage – Guidelines, Explanation, and Caution
  • ANSI A108.02 section 4.3.8 – Grout Joint Size
  • ANSI A108.02 section 4.3.8.1 – Running Bond / Brick Joint Patterns
  • ANSI A108.02 section 4.3.8.2 Running Bond / Brick Joint and Any Offset Pattern (for your convenience, I have quoted this section here): 

As you can see, ANSI A108.02 4.3.8.2 is very clear. When this requirement is followed along with installing tile that meets the manufacturing standards of ANSI A137.1 and when the substrate flatness standard for tiles with at least one edge 15” or longer is applied, the correct mortar is selected and mixed properly, the correct trowel is selected and used properly by an adequately trained and skilled installer, a successful finished installation should occur. (Note: the substrate flatness requirement for a 12” x 24” tile only allows a maximum permissible variation of 1/8” in 10’ from plane with no more than 1/16” variation in 24” when measured from the high points in the surface.)

Lippage can become a real problem when the lights are turned on.

Allow me to state this another way:

  • Using tile that meets the requirements of ANSI A137.1 for Nominal Size, Caliber Range, Warpage and Wedging
  • Installing that tile on a substrate that meets the ANSI A108 requirements for flatness
  • Following the ANSI A108.02 4.3.8.2 and/or the tile manufacturer’s requirements for maximum offset
  • Following the details of the appropriate method selected from the TCNA Handbook for Ceramic, Glass, and Stone Tile Installation
  • Selecting the correct mortar or adhesive for the type of tile being installed and application it is to be installed in
  • Mixing the mortar or adhesive per its manufacturer’s instructions
  • Selecting the correct trowel and using it correctly to achieve the bond coat coverage rates required for the system equals a successful, long-lasting installation that will please the owner and end user.

Note that ANSI A108.02 4.3.8.2 states “…specifier and owner must approve the mockup and lippage.” In my opinion, the expense of purchasing an adequate percentage of tile to install the required offsets can be very minimal when weighed against the potential for lippage and lighting-related failures that can occur when manufacturer instructions and tile industry standards are not followed.

Industry standards and manufacturer recommendations of 33% or less offset for tiles with one or more sides 15” or greater are required because of the manufacturing process for tile. When ceramic tile is heated and cooled in the kiln, warpage can occur. This is a normal result of the manufacturing process. Many tile factories are excellent at controlling warpage, but it cannot be completely removed. That is why there are limits for how much warpage a tile can have detailed in ANSI A137.1 for tiles that are manufactured to meet that standard. Whether or not a given tile meets the warpage limit of ANSI 137.1 can be found in the information printed on the carton or on the manufacturer’s technical data sheet, or by contacting the manufacturer.

The NTCA Reference Manual contains valuable information about wall lighting and lippage control devices.

You are absolutely correct in noting that lippage resulting from a layout or offset pattern or other factors can become a real problem when the lights are turned on. This is especially true for walls when the lighting grazes the face of the wall or when there is a sharp angle of incidence from natural light on a floor. I have listed references on the following page for more information on this topic.

You are also correct in noting that lippage tuning devices can help mitigate these issues. The job of these devices is NOT to take the place of any of the standard requirements I described above, but they can be a useful tool to help installers remove the last bit of human error (typically a maximum allowed 1/32”) and to hold the tiles in place while the bond coat cures. I have listed references below for more information about these devices.

I do not know why manufacturers or distributors might show tiles in an offset pattern that is different than what is required for a specific tile or by industry standards. It could be oversight or lack of knowledge by the person designing or creating the mockups.

You are correct that it very often falls to the tile installation contractor and installer to be the industry expert that understands everything I have described above. The installing contractor and the installer are the last line of quality control before the installation goes in. When or if there is a problem after installation, it is the installer and installation contractor that gets the call. The installation contractor needs to have an excellent working knowledge of the industry standards, methods and best practices to be able to adequately communicate the potential issues during the bidding process and BEFORE the installation takes place. To avoid issues, contractors and installers should empower themselves with this knowledge and know how to identify problems and to stop and identify a resolution before proceeding with the installation. Other trades and professionals such as general contractors, architects, specifiers and designers will respect a knowledgeable tile contractor that is able to clearly communicate what must be accomplished and why. Mockups are a key element of this process and are strongly recommended.

I described the key elements of the ANSI standards that pertain to this discussion of your questions. In addition, there are several other key areas you can use to inform yourself and communicate to other about this subject. They include:

  • 2018/2019 NTCA Reference Manual section on Critical Lighting Effects on Tile Installations on pages 125 – 132.
  • 2018/2019 NTCA Reference Manual section on Lippage Control Devices and Edge and Lippage Mechanical Tuning Devices on page 172.
  • 2018 TCNA Handbook section on Substrate Requirements.  See the section on Substrate Tolerances and Large Tile on page 31.
  • 2018 TCNA Handbook section on Lighting and Tile Installations on page 34.
  • 2018 TCNA Handbook section on Flatness and Lippage on page 36.
  • 2018 TCNA Handbook section on Grout Joint Size, Layouts, and Patterns on pages 37-38.
  • 2018 TCNA Handbook section on Finished Tilework on page 39 (especially the section on “Visual Inspection of Tilework”)

I encourage you to read and become familiar with all of the standards, methods and best practices I’ve described above in your NTCA Reference Manual, TCNA Handbook and ANSI standards. This will help you be even more confident in describing why installation standards and manufacturer instructions must be followed. Any deviation outside of following them often becomes risk accepted by the installation contractor because at the beginning, middle and end of every job, the tile contractor is the industry expert.

As you and I know, tile isn’t simple or easy. Sometimes, for very good reasons, we can’t always give the owner or specifier what they think they want. Contractors such as yourself that have access to the NTCA member benefits of technical support and education can better communicate the need to apply recognized industry standards, methods and best practices for successful installations. As you know, membership in the National Tile Contractors Association is a major source for help in understanding the standards and how to apply them and avoid issues BEFORE they happen.

We encourage designers, architects, GCs, and specifiers to attend our many workshops and other education programs, or to become an NTCA member themselves. Please feel free to direct them to our website and calendar of events at www.tile-assn.com and click on the Free Educational Workshops link under Education & Certification on the home page. You are doing a great job in asking the right questions. I hope this helps. 

Looking for documentation for flooded houses with tile floors

QUESTION

We are working with flooded storm victims from Hurricanes Harvey and Irma. The issue we are facing is that these homes were inundated with 3-8 feet of water for 2-7 days…category 3 water, which includes sewage and other toxins. The insurance companies and the National Flood Insurance Program refuse to consider this flooring damaged and are not paying for it.

Our research has shown us that, after a period of time after the storm, these tiles become loose due to water finding its way under the tile and causing damage to the adhesives. In addition, this also allows contamination to the flooring system. It was also noted that some ceramic tiles are porous, and the tiles themselves could be damaged or contaminated.

Based on the conditions above, we are looking for some documentation or recommendations stating the following about the tile floors in this situation (average age of tile install 5-10 years):

1. That the tile floor is recommended to be replaced due to the reduction or loss of adhesion, and/ or

2. That the tile flooring itself, including the adhesive, may be contaminated and should be replaced.

We find it hard to believe that an average-aged home with tile floors would be completely sealed and have no water intrusion into the tile flooring system. I would love to discuss this with your team after you have discussed this issue. Thank you very much and we appreciate anything you could do to help us and the recent flooding victims.

ANSWER

There are a number of standards and best practices that guide tile installations in America. Installation and material standards and specifications are found in American National Standards Institute (ANSI) A108; A118; A136; A137.1; A137.2; A137.3. Installation best practices, methods and guidance are found in the Tile Council of North America (TCNA) Handbook for Ceramic, Glass, and Stone Tile Installation. In addition, manufacturer instructions for the application and installation of their setting materials and related products used in tile installations must be followed for every
installation.

Installation standards, methods and materials will vary depending on the particulars of any given installation. Is it for example:

  • A floor, wall or ceiling.
  • A wet area such as a shower or a steam room.
  • A residential or commercial installation.
  • Is the supporting structure wood or concrete or steel.
  • Is the tile ceramic/porcelain; stone or glass.
  • And many other considerations.

Because there are applicable standards, methods, best practices, procedures, materials and numerous details that apply differently to each of these installation types, one generic analysis cannot possibly apply to each. Installations that have been flooded and constructed to the requirements of tile industry standards, methods and best practices can withstand significant amounts of moisture better than other products. In flooded situations, forensic investigations may need to be conducted to determine the next steps.

For this reason, NTCA strongly encourages you to contact a NTCA Recognized Consultant to review your cases. Find a recognized consultant by going to the NTCA website at www.tile-assn.com and searching for recognized consultants under “Find a Member.” As an association of tile contractors and professionals, NTCA itself does not provide these consulting services.

Mark Heinlein, NTCA Training Director

Fire and Sound Rating for Wall Assemblies

QUESTION

I am a design consultant, working on existing nearly 100-year-old structures. We need to be in compliance with current code for fire separations one- and two-hour.

Due to the historical aspects of some of the structures we cannot do much to the exterior but can enhance fire safety when doing alterations that affect the interior walls and floors.

Since the Space Shuttle uses ceramic tiles on the outside of the hull to preserve the lives of the crew from the inferno re-entry heat, why can’t ceramic tile be a part of the fire-rated floor and possibly ceiling assembly?

The intrinsic value added is we may be able to make the assembly thickness narrower, thus keeping the first floor and existing ceiling at the 7’-6” minimum clear building code height. Net results could be no fire sprinklers required, in certain situations, greater fire safety, lower cost for the upgrade and possible new avenues for upgrading older existing structures using something with thousands of years of historical reliability that goes through several thousand degrees of heat, to get produced.

ANSWER

I can direct you to the 2018 edition of the Tile Council of North America Handbook for Ceramic, Glass and Stone Tile Installation.

In the TCNA Handbook you will find method RW800-18 and associated descriptions and details for Fire and Sound Ratings for Wall Assemblies. This method begins on page 293 and includes a variety of details and information on materials and layers to design and construct fire rated tile assemblies.

Copies of the TCNA Handbook are available for purchase through the NTCA store at www.tile-assn.com. I hope this helps! 

Mark Heinlein, NTCA Training Director

Safety precautions for the newly-released silica standards

QUESTION

We are reaching out to touch base on the newly-released silica standards in construction. You guys come in contact with a number of other contractors on a day-to-day basis. We are wondering what safety precautions other contractors are taking to better align themselves with OSHA’s standards.

We had OSHA inspectors on a project today at a local college. They have interviewed our employees in regards to company policy, etc. We have yet to receive feedback from our guys or receive formal notification from the GC.

Our guys use vacuums with dust masks when grinding tile or mixing mud. We grind outside when possible. Other than that, it has been a supervised common-sense approach to what we feel is appropriate. Obviously we want to remain compliant and keep our guys safe. We are looking for any input or direction you guys can provide to help us better formulate a compliance policy to keep everyone happy and safe. Look forward to hearing back from you.

ANSWER

Thanks for getting in touch with us about this very important topic.

NTCA has prepared some documentation for you to develop a Silica Exposure Plan to help you understand and meet OSHA Regulation requirements. It can be found on our website at this link: https://www.tile-assn.com/page/PositionStatLibrary.

NTCA is working with experts from the Tile Council of North America (TCNA) and OSHA to increase our knowledge and stay up-to-speed on the latest developments of the OSHA Silica Regulations. An important aspect of the regulation is known as Table 1. This table lists the tile installation jobsite tasks that commonly create exposure to silica dust. The tasks on this table are currently in the process of changing. We do not yet know exactly what changes are being made, but we anticipate that the tasks will become better defined for us to better plan how to stay in compliance.

NTCA always discusses silica exposure and techniques to avoid creating dust, or ways to properly capture the dust we have to create, at all of our training programs such as NTCA Workshops and NTCA Regional Training events. When these programs are near you, please be sure to attend. 

We are also working with TCNA and OSHA to present two in-depth silica sessions and workshops for Coverings. Attending these workshops at Coverings will be a great way to gain direct knowledge about what is required for your company to be in compliance.

Being in compliance is quite a bit more than simply moving the grinding outside or using a vacuum and a dust mask. You must have a written exposure control plan with documents that detail how you will handle certain dust generating tasks for every job and every job site. You must also have a person identified as the “Competent Person” on every job site that will ensure your plan is in place and working on the job.

Knowing a jobsite-specific task’s “Personal Exposure Limit (PEL) is a major component of determining whether your jobsite’s require certain control measures. PELs are cumulative for multiple tasks and for the length of time persons are exposed to the task. It is a lot to discuss in a simple email, but it all adds up to determine the level of protection or controls required.

As I mentioned, grinding outside isn’t necessarily an easy solution. We must protect other trades and the general public from exposure to any silica dust contractors generate on our jobs. General contractors must calculate the PELs for all trades contributing to the overall PEL for the entire job site. They will want to know how you will be containing or reducing dust-generating practices and you will want to know how the other trades are doing the same and contributing to the overall job site environment.

You will want to become familiar with the engineering controls or mechanical control measures that can be put in place to reduce dust below certain exposure levels, or eliminate it entirely. An engineering control might mean using a carbide scoring tool to score and snap cement board instead of using an angle grinder to cut it. Others range from tools we already use every day such as wet saws and snap cutters to grinder shrouds and HEPA vacuums. Speaking of vacuums, not every Shop-Vac®-type vacuum works to collect silica dust and keep it from becoming airborne. Specific vacuums are required.

Simple dust masks don’t do the trick. If engineering controls alone don’t keep your job site PEL beneath minimum thresholds you may need to look at a respirator program. Such a program may require fitness and physical testing of your employees to ensure the respirators work and they are healthy enough to wear them.

The key is to understand Personal Exposure Limits, tasks listed in Table 1, Engineering Controls, writing a company plan, providing employee training, and putting your plan in place. It sounds like a lot, but it is a good health and hygiene best practice for you and your employees. 

I may be making this sound more complex than it might actually be. Please take a look at the documents available on the website and read what OSHA has to say on their website at https://www.osha.gov/dsg/topics/silicacrystalline/. I expect you will be getting some excellent feedback from your employees. I encourage you to contact the OSHA inspector that visited your job site – I am sure they will be willing to help your understanding of the regulation. 

Mark Heinlein,
NTCA Training Director

What should the relative humidity percentage be to set tile?

Laticrete logoQUESTION

I am looking for the relative humidity percentage in a newly-poured concrete slab to be able to set tile. 

ANSWER

Unless installing an UN-bonded mortar bed, all TCNA Handbook methods for installing on concrete call for the slab to be well cured, dimensionally stable, and free of cracks, waxy or oily films, and curing compounds.

Some manufacturers of uncoupling membranes may have instructions allowing for the use of their membrane over newly poured concrete since the membrane may act as a conduit for the concrete to properly cure during the early stages of the curing process. The membrane manufacturer would have to be contacted to verify and support this for use of their product.

Installing on a slab with excessive internal moisture can be problematic. Installing on a green slab presents the potential for additional unknown factors.

Many factors come into play when considering relative humidity (RH) in a slab. In a new slab, curling of the top surface (especially at control joints) may occur causing the slab to exceed variations in flatness tolerance for a tile installation. As a green slab cures (and curls), debonding or cracking of the tile bonded to it may also occur. Your 2018/2019 NTCA Reference Manual includes an excellent discussion on Ceramic Tile & Stone Installations over Concrete Substrates on pages 50 – 61. The troubleshooting guide on page 54 includes a discussion of identifying problems/causes/cures for excessive internal moisture in a concrete slab. It also references the test procedures for determining safe levels for moisture in a cured slab.

In addition to consulting the NTCA Reference Manual and membrane manufacturer, it is important to involve your setting-material manufacturer in the discussion for selecting the correct bonding and grouting products to adhere to and properly handle the moisture emanating from the slab. 

Mark Heinlein,
NTCA Training Director

Waterproof membrane for concrete substrate

Laticrete logoQUESTION

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?

ANSWER

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. 

Robb Roderick,
NTCA Technical Trainer

What do you use to clean 100% silicone caulking

QUESTION

I wanted to ask you about what you used to clean the 100% silicone caulking when you did the caulking demonstration at a recent workshop? Thanks!

ANSWER

I used water with a few drops of dishwashing liquid in a spray bottle. Install sealant, spray the bead of sealant, then strike off excess and wipe on paper towels. If you want to strike again to dress it up just spray the area again. This will keep it from sticking. Denatured alcohol, window cleaner, and a variety of other things are often used in the same way. Whatever you use make sure it is approved by the manufacturer of the sealant. Using non approved chemicals or methods can lead to issues like incomplete curing of the sealant joint. 

Robb Roderick, NTCA Technical Trainer

Should you tile to the walls or leave a small space?

SponsoredbyLaticreteQUESTION
When installing floor tiles, should you tile to the walls or leave a small space for movement and flexibility?

exp-01ANSWER
To answer your question about whether to leave a space where a floor meets a wall – Yes! A gap of approximately 1/4” should be left at all changes in plane (for instance where a floor meets a wall) around the perimeter of the installation. This gap should be present in the underlayment and tile. If no trim will be installed to cover the gap, a “soft joint” can be made with appropriate sealant, or certain trim profiles can be installed to accommodate movement and expansion. This gap should also be left where tile abuts cabinetry, pipes or other permanent fixtures. Any other change in plane such as where a wall meets another wall must also have a soft joint installed to allow for movement and expansion. Also, expansion joints must be properly placed and installed in the tile field depending on the location and size of the installation. Additionally, control joints and saw cut joints in concrete must be honored through the surface of the tile to avoid future cracks in the finished installation. These specifications and the many, many other details related to a successful tile installation can be handled by your qualified contractor and certified labor.

 

Tiling over a painted surface

QUESTION

I know the TCNA Handbook for Ceramic, Glass and Stone Tile Installation says that paint is not a recommended surface for tile installation but here is the situation.

I am doing a commercial job and did a wall of large subways. The owner was taken with the installation and has tripled the areas she now wants tiled. Of course she already paid for the drywall guys and the painter to finish these areas. What I should I recommend as best and acceptable course of action? Of course money is an issue.

ANSWER

Congratulations on having your scope of work triple in size.

Installing tile on gypsum board and painted gypsum board is always an intriguing question to consider. It is always best that the design and construction of the substructure and selection and installation of the substrate be done to meet the requirements necessary to support a tile installation.

As you already know, TCNA Handbook methods W242-18 (Organic Adhesive) and W243-18 (Cementitious Bond Coat) are for installing (direct bonding) ceramic or glass tile on a substrate of gypsum board fastened to wood or metal studs. In these methods, the Preparation by Other Trades section states: “Gypsum board… to be installed per GA-216.” and “Gypsum board face layer joints – treated with tape and joint compound, bedding coat only (no finish coats). Nail heads, one coat only.”

I break down (and paraphrase) those statements in this way:

  • Gypsum board is to be properly installed (by the gypsum board installation contractor) as described by the Gypsum Association’s GA-216 (which further references GA-214).
  • The face layer joints of the gypsum board are to be treated with (joint) tape applied to a bedding coat of joint compound.
  • Nail (fastener) heads are to receive one coat only of joint compound.
  • No additional finish coats of joint compound are to be applied (to the face layer joints or to the fastener heads).
  • These instructions say nothing about painting the gypsum board, which indicates it is not to be painted.

In other words:

  • The board is not being prepared for painting, papering or any other surface finish.
  • The board must be fastened and prepared to support a tile installation as the surface finish.
  • Additional considerations for a vertical tile installation on gypsum board include:
  • Weight of the installation
  • Deflection ratings
  • Flatness of the substrate

° For Organic Adhesive: Refer to ANSI A108.4. Substrate flatness tolerances are listed in ANSI A108.01 2.5.2.1 and ANSI A108.02 4.1.4.2.2. Additional flatness tolerances are listed in the TCNA Handbook Method W242-18 Preparation by Other Trades section.

° For Cementitious Bond Coat: Refer to ANSI A108.5. Substrate flatness tolerances must not exceed those required for vertical surfaces as defined ANSI A108.02 4.1.4.3.2 and as listed in the TCNA Handbook Method W243-18 Preparation by Other Trades section.

° See also TCNA Handbook Substrate Requirements on pages 30 – 33

  • Environmental Exposure

° Methods W242 and W243 are rated as Res1 (Residential Dry) and Com1 (Commercial Dry). See TCNA Handbook pages 44 – 47.

° See also TCNA Handbook Backer Board Selection Guide Direct Bond to Wood or Gypsum Wall Board – Caution on page 20.

  • Bonding the tile to the substrate

° For any installation, the correct setting material or adhesive must be selected to bond the tile to the substrate.

° In a gypsum board installation, the setting material or adhesive must bond to the paper face and joint compound.

° If the gypsum board has been painted, the paint is bonding to the paper and joint compound and the setting material must bond to the paint.

Finally, to get to your question, the NTCA Reference Manual contains a list of Questionable / Unsuitable Substrates (see page 30 in the 2018/2019 edition).

Paint is listed as a Questionable Substrate.

The NTCA Reference Manual advises: “Questionable substrates are substrate types that when properly designed and prepared can receive direct bond applications of ceramic tile and stone. Some questionable substrates conform to specific ceramic tile and stone industry installation methodology when applicable requirements are followed. In addition, the use of specific installation materials designed for unique applicant can result in a successful installation. Consult ceramic tile and stone installation manufacturers for their recommendations.”

What this means for your installation is, once it has been determined the gypsum board and its supporting structure have been properly designed, constructed and installed to support a tile installation, consult your setting-material manufacturer to determine which of their adhesives or mortars (and possibly primers) are recommended to bond the tile to the painted gypsum substrate. Obtain from them a job-specific written warranty covering the installation.

If you find the walls have not been properly designed, constructed and installed to support a tile installation, speak with the owner, general contractor and other trades to discuss what needs to be done to bring them into tolerance. Generally speaking, when you install the tile, you are accepting the substrate. If you need to re-fasten, prepare or render the substrate for flatness, make sure you have an approved change order to get paid for the work.

The NTCA Reference Manual goes on to say “Certain questionable substrate types can receive ceramic tile and soon installations when installed with a…. cleavage membrane/lath and plaster wall assembly.” This means another option would be to follow TCNA Handbook Methods W221 and W222 which can use the installed gypsum board as a solid base for a mortar bed installation.

Please watch this episode of Question Mark on NTCA’s TileTV that shows a commercial wall substrate that did not meet standards for a tile installation: http://www.iwantmytiletv.com/index.php?video=1B7E5CA9 or https://bit.ly/2T3f5AV

I hope this helps.
Mark Heinlein,
NTCA Training Director

Does this look like a troweling error or product defect?

QUESTION

Have you guys ever seen this before? It seems to be where the mesh is holding the tile together. This is a 2” x 4” glass mosaic (approximately a 12” sheet). I know this is asking a lot without actually seeing the install and product in person. Note the “voids” around the periphery of each piece of tile. Does this look like a troweling error or product defect to you? Please let me know. I’d love to know your insight on this.

 

ANSWER

You are correct – this is difficult to fully and accurately assess without being on site and personally inspecting an uninstalled tile, inspecting the completed installation and interviewing the installer.

However, based on the photo you sent I would hazard a guess that the anomalies we are seeing are uncollapsed ridges made with an approximately 3/16” V-notch trowel. 

Mark Heinlein
NTCA Training Director

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