Safety precautions for the newly-released silica standards


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.


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:

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 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. 


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?


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


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!


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?

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

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


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.


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 and ANSI A108.02 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 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: or

I hope this helps.
Mark Heinlein,
NTCA Training Director

Does this look like a troweling error or product defect?


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.



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

Round drain or linear drain


We have a customer that set the drain back against a wall in a shower. It’s in California and it’s an outside shower. Shouldn’t this be a linear drain, or is it okay to have a 2”-3” drain against a wall? The pitch seems to be okay. The actual issue is people were slipping. It’s an outdoor shower for a community pool with older tile. We’ll be suggesting a tile replacement and, if they want to keep the existing tile, an epoxy coating option to help mediate the slip-fall issue. Thank you. 


You are correct in reasoning that a linear drain would likely be most appropriate for a shower drain placement that is very close to a wall. With a linear drain, the floor of the shower can be uniformly sloped in one or more flat / properly sloped planes toward the sides and ends of the drain. Having said this, the waste pipe needs to be carefully located and sized to accommodate the linear drain being used.

With a round drain, it may be more difficult to obtain the correct slope (minimum 1/4” vertical per 12” horizontal) consistent slope to drain. A typical round clamping ring drain and many round bonding flange drains may not be able to be positioned close enough to the wall to allow for proper waterproofing connections and/or slope to the drain. There may, however, be some round drains especially designed to work properly in close proximity to a wall while still allowing for proper waterproofing connections and slope to the drain and/or weep holes. 

Mark Heinlein,
NTCA Technical Director


Cracked and/or chipping polished and honed field tile


I am in need of your expertise. I have a client that installed Porcelain Statuario polished and honed 30” x 30” and 15” x 30” field tile in both a lobby floor and a dance floor of a country club. It’s quite a large area, so there were about 912 of the 30” x 30” tiles and about 132 of the 15” x 30” tiles, in total. About 80 tiles are exhibiting cracks and/or chipping (see pictures below). Any thoughts or ideas will be gladly welcomed.


It appears the failures in this installation may be caused by less than the standard requirement for bond coat coverage (80% in a dry area), and/or the tiles may not have been tested to or meet the ANSI A137.1 requirement for breaking strength, or something else that is not possible to determine from these photographs.

As a trade association representing tile contractors, NTCA is able to provide pre-installation technical assistance based on recognized American tile industry standards, methods and best practices. We are not able to provide detailed analysis or consultations for post-installation failures.

Given that this installation is already in place and is failing and the apparent high-profile setting of the installation I suggest that an on-site analysis and failure determination be conducted by one of NTCA’s recognized consultants, all of which can be located at this link: These consultants can perform a third party analysis and determine the cause(s) of failure.

I hope this helps.
Mark Heinlein,
NTCA Technical Director

Guidelines for installation of thin porcelain panels


I am looking for installation guidance for 30” x 60”, 1/4” thin porcelain panels in a floor application over concrete. It is a high rise building so I assume it is post-tensioned concrete assembly for the floors. Does TCNA have any guidelines?

Furthermore, the City of Minneapolis requires a sound damping product be used under hard surface flooring such as porcelain tile. 

While I have received information from one thin-panel distributor and from LATICRETE that this thin material should not be used over a sound control membrane, the architectural rep for the product manufacturer says their thin panel can be treated like any other porcelain tile. However, she will not provide any documentation that validates that statement. Can you perhaps help me get something from the manufacturer that sheds light on this question? 


There are several points necessary to discuss regarding your concerns.

Do you own a copy of ANSI A137.3 / ANSI 108.19? These are the material specifications and installation standards for Gauged Porcelain Tiles and Gauged Porcelain Tile Panels/Slabs. I refer to these as “GPTP” for short. This standard defines what GPTP is, where it can be used, how to properly install it and specifies the training required for persons installing it. If you do not own a copy of this standard, it is available for purchase from the NTCA’s bookstore at: or 

You are correct that any installation on a post-tensioned above ground slab will require special considerations. TCNA Handbook method EJ-171 addresses some of these concerns. It is the responsibility of the project’s specifier (i.e. architect, structural engineer, etc.) to develop the jobsite-specific drawings, material and installation specifications that will guide your installation. This includes details for movement joint placement. If these documents and clear instructions are not included as part of the statement of work or drawings, you need to request them.

ANSI A137.3 / A108.09 defines the “Gauged” (thickness) component of Gauged Porcelain Tile / Panels (GPTP) in two categories: 3.5mm – 4.9mm thick and 5.0mm – 6.5mm thick. The standard allows for installation of the thicker 5.0-6.5mm material on floors and walls. The 3.5-4.9mm thick material is for use on walls only (not floors). Some manufacturers will allow for the use of their thinner GPTP material on floors. I strongly recommend you make absolutely certain that you receive a jobsite-specific warranty from the GPTP manufacturer before installing thinner (3.5-4.9mm) tiles/panels on a floor.

Regarding use of a sound damping product under GPTP – ANSI A108.19 Section 3.0 (Existing Surfaces/Substrates) states in subparagraph 3.3 “Do not install over unstable, compressible surface materials or coatings.” I suggest contacting the sound reduction membrane manufacturer for more specific information for use of their product with GPTP.

Proper substrate preparation and selection and use of membranes and mortar and trowel and installation techniques are very critical for the successful installation of GPTP. Proper training for installation of this product is required by the A137.3/A108.19 standard. NTCA and product manufacturers provide this training for persons who will be specifying and installing the material. In summary, the specification should be very clear in referencing all industry standards for installation of GPTP. The GPTP and setting material manufacturers should provide you with a clear jobsite-specific warranty and installation instructions for use of their product(s). The installers are required to have training. If this is not the case, you will want to carefully consider your acceptance of risk with this installation. If the manufacturer cannot provide you a clear warranty, I would consider that a red flag.

I hope this helps. 

Mark Heinlein,
NTCA Training Director,
NTCA Technical Trainer

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