Locating and interviewing a tile contractor

QUESTION:

I’m a homeowner looking to have tile work done on my new home. I’ve had bad experiences with poor tile installations on my last house. We had a shower that leaked and caused an extensive amount of damage. How can I know if the contractor I hire this time is qualified and will do a good job?

ANSWER:

Begin by locating a National Tile Contractors Association Member contractor. Through their professional association, these companies are connected to the highest levels of the tile industry and own the recognized tile industry standards, methods and best practices that guide their installations to success. Then require a Ceramic Tile Education Foundation Certified Tile Installer (CTI) to perform the installation. These persons are known to the tile industry as Qualified Labor and have proven their ability to understand and apply tile industry methods, standards and best practices through an aggressive written and hands-on certification process. They can be located in your area by exploring these links:

When you interview any tile contractor:

  1. Ask them if they own and use the TCNA Handbook and ANSI Standards. Ask them which Handbook method they will use to construct your project. This will help you determine if the contractor you are interviewing owns and uses the recognized industry standards that will produce a great-looking and long-lasting installation for you.
  2. Ask them if they are a CTEF Certified Tile Installer (CTI) or if they hold Advanced Certifications for tile installations (ACT). Tile installers have been critically examined by the only nationally-recognized, third-party training and certification foundation on their knowledge of the recognized methods and best practices, and their ability to use them to produce a great-looking and long-lasting installation. A CTI will have a unique number assigned by the Ceramic Tile Education Foundation.
  3. Ask them if they are a member of their professional association. For tile contractors, it is the National Tile Contractors Association. Detailed technical support based on tile industry standards is a hallmark benefit of contractor membership.
  4. Ask them if they are licensed to work as a tile contractor by their state’s licensing board. (Not all states require licensing.)
  5. Ask them for references and a portfolio of work. Call their references. Review their portfolio. Preparation is everything. Ask them what type of prep work they will do before installing the tile.

Following this process should help you locate and employ a contractor that will perform the best installation for you.

Offset patterns dos and don’ts

Question

It appears to my untrained eye that most 12”x24” tile is laid so that each abuts the two adjacent tiles by 50% each. However, the sales associate said some governing body (Tile Layer’s Association??) had rules against that because of “lippage?” Are there rules on how tile should be laid? If so, where is the resource for that? I’d like to know, as being the homeowner, I assume I’m ultimately responsible for catching mistakes in the construction of my new home.

Also, is it better to purchase (at high cost) precut 4” x 12” or is it acceptable to have those cut by installers from 12” x 24”. A sales associate said the former is the better option.

Answer 

These are excellent questions that are answered by the tile industry’s written standards and best practices.

It sounds like you are selecting tile for a builder’s installer or tile contractor to install. I suggest asking your builder if their installer or contractor owns and applies the methods and standards in the Tile Council of North America Handbook for Ceramic, Glass and Stone Installation (TCNA Handbook), and the American National Standard Specifications for the Installation of Ceramic Tile. These are the documents that answer your questions.

The associate you are working with is giving you solid advice based on these standards. The retailer you are working with is a strong supporter of NTCA and their staff and associates, many of which have attended our training programs, are knowledgeable about these things.

50% offset for 12” x 24” tile

ANSI A108.02 section 4.3.8.2 is where the answer is. I will paraphrase what it says – When tiles with sides longer than 15” are being set with their long sides next to each other they shall be set in a pattern with an offset of 33% or less. If an offset more than 33% is desired (such as a 50% offset), the specifier and owner must approve a mock-up and agree to the lippage that may result from this type of pattern being installed.

The reason for this is that some tiles have what is called warpage as part of their manufacturing process. Warpage is when the tile is bowed in the middle. The ends of these tiles may be lower than the middle of the tile. When tiles longer than 15” are set next to each other in a 50% offset, this puts the high part of the middle of one tile directly opposite of the low part of the end of the adjacent tile. This can result in a difference in height elevation of the plane between the two tiles. This difference in the plane is known as lippage. To quote the TCNA Handbook: “Lippage is a condition where one edge of a tile is higher than an adjacent tile, giving the finished surface an uneven appearance. Lippage is inherent in all ceramic installation methods and may also be unavoidable due to the tile tolerances, in accordance with ANSI A137.1.”

Not all tiles have warpage. There are industry standards that describe acceptable warpage. Some tiles are made to meet those standards, some are not. The tile manufacturer can tell you if their tile meets the standard for warpage. It is in ANSI A137.1.

Some manufacturers will have specific offset requirements for their tiles. They may require a 20% or 25% maximum offset.

So – if you would like a 50% offset, you need to ask your tile contractor to lay them out or physically install a few so you can view them as they will look in the finished installation. At that time you would approve and accept (in writing) any lippage that occurs as a result of setting them at a 50% offset. You will own and live with this installation – it is your decision to approve or reject the mockup.

Cutting 4” x 12” tiles out of 12” x 24” tiles:

The TCNA Handbook for Ceramic, Glass and Stone Tile Installation states: “Tiles should not be field-cut to size to accomplish modular patterns or to align grout joints, as field-cut edges will be dissimilar from factory edges and cannot be held to the same squareness tolerance.”

This is not a desired practice. In reality, it is not less expensive as your tile contractor should rightly be expected to charge labor and materials to cut down and smooth or hone the tiles. The tile contractor likely has excellent tools, but they may not be of the same grade as the tile factory and with human error, there may be variations from tile to tile after they are cut. Expect the labor price to increase, as more time is needed to ensure all tiles are well matched and finished.

Depending on the tile body and glaze, this practice may present opportunity for chipped tiles. A large amount of additional tile may need to be purchased at the outset to account for this possibility.

To ensure that you get all of the correct technical information you need for your installation, I strongly encourage you to employ an NTCA member contractor and a CTEF Certified Tile Installer (CTI). These contractors and installers own, understand and apply the tile industry’s recognized standards, methods, best practices and follow manufacturer instructions in the installations they construct. NTCA Members and CTEF CTIs have direct unlimited access to the NTCA/CTEF technical team for training and detailed industry standards-based support in every installation they construct.

Please review the Ceramic Tile Education Foundation’s homeowner’s guide to hiring a qualified installer and visit the NTCA site to find an NTCA member contractor in your area.

Why is the shower leaking?

I have a shower I installed two months ago that is leaking.  I did my installation in the same way I have for the past 15 years in accordance to manufacturer instructions. I have never had a leak in the past and am not sure what went wrong. When I plug the shower and turned the shower on to run the water came through the downstairs ceiling. The homeowner is extremely upset and the GC wants me to tear it out immediately. Trying to figure the best course of action.


NTCA Technical Team: We have had many questions about leaky showers. Before you tear anything out it may be best to make sure there is not a plumbing leak. Or possibly a leak from some other reason than your installation. There have been situations where other trades could be responsible, and the situation deserves a thorough investigation.  

The source of a leak isn’t always where it manifests itself. Water runs downhill and can leak from one side of the shower then pool on the other side.  A moisture meter can sometimes help in these type investigations to find the origin of the leak.  

Sometimes, showers can leak-only when the shower is in use because water has gotten behind an escutcheon. They also can leak only when running from a poor connection between the mixer valve and shower head. A third possible reason is a screw or fastener could have punctured the water supply from the mixer valve to the shower head.  Has the plumbing been capped off and a high-pressure test done to look for leaks?

Many time people think it’s the pan because it only leaks while running. Performing a flood test by plugging the drain and filling with water from another source than the showerhead will tell you and the GC the soundness of your pan.

Some fixture and shower door installers can unknowingly puncture waterproofing.  The NTCA Reference Manual has a section that describes the risk of leaks when shower doors are improperly installed. It includes a letter you can copy and send to the glass door installation company to inform them about the waterproofing and their responsibility to protect the watertight integrity of the shower system you installed.  

There is also information in ANSI that explains that any damage to the tile work after you leave is not your responsibility,  

Removing and replacing a shower like this is very expensive. Double check every possible scenario you can, or you could waste time and money and the customer may still have a leaky shower.

Response:

Thank you so much. We discovered the leak was from the shower door installation.

Can I use wall tile on my shower floor?

Question 

The NTCA Technical Team recommended that this inquirer consult the technical data sheet and the manufacturer of the tile to be sure the wall tile is rated for use on a shower floor. Just because it looks good doesn’t mean it will perform well, especially in a challenging installation. 

I am building a new home and learning things I never knew. One is regarding what tile can be put on a shower floor. I want a shower as in the attached inspiration photo. Apparently, they used a tile that is now discontinued. The new version I like is approved for a shower floor. However, it is expensive and has divots/irregularities. I was hoping for something smoother and in budget.

Most black subway tile is not annotated as for shower floors. However, my sales representative is telling me that it is perfectly fine to use a wall tile on a shower floor. She is recommending a specific glazed ceramic wall tile 3”x12” (black glossy). Is she correct?

ANSWER

Any tile considered for use in any application should have the manufacturer’s approval for intended use. I suggest asking your distributor/salesperson to obtain the technical data sheet (TDS) for the tile you are interested in. The TDS should specifically include information if the tile is acceptable for use on a floor in a wet area (such as a shower floor). If the TDS does not include this information, you can call the manufacturer directly to request this information or select a tile that is specifically rated for use on a shower floor.

Additionally, durability of the tile in this application may or may not be affected by the type of shower pan being specified for this installation and its ability to properly support a soft bodied wall tile.

Another consideration is the pattern and drainage system. If a running bond pattern is used (with a conical pitched floor to a center drain) it would result in lippage and accompanying puddling. A running bond pattern with a linear drain system could help minimize any puddling.

As you have discovered, tile is a complex science and art. One of the most critical installations to construct is a shower. To ensure that you get all of the correct technical information you need for your installation, I strongly encourage you to employ an NTCA member contractor and a CTEF Certified Tile Installer (CTI). These contractors and installers, understand and apply the tile industry’s recognized standards, methods, best practices and follow manufacturer instructions in the installations they construct. NTCA members and CTEF CTI-certified installers have direct unlimited access to the NTCA/CTEF technical team for training and detailed industry standards-based support in every installation they construct.

Please review the Ceramic Tile Education Foundation’s homeowner’s guide to hiring a qualified installer: www.ceramictilefoundation.org/homeowners-guide-to-hiring-qualified-tile-installer

To find an NTCA member contractor in your area: www.tile-assn.com/search/custom.asp?id=2759

To find a CTI installer in your area: www.ceramictilefoundation.org/find-certified-tile-installers

I hope this helps.
– NTCA Technical Team

Proper construction of shower curbs

Question:

We have a project that we are looking at that has showers that will receive liners, mud and tile.  The curbs have been constructed out of pressure-treated 2″x4″s that will get wrapped with liner and wall board before tile is installed. Are pressure treated 2x4s acceptable to use in this application? I have read they are not but could not find anything on this in the TCNA guidelines.

Answer:

Shower methods, in the TCNA Handbook under requirements for wood studs says they must be dry and well braced. The general requirements for wall bracing is found in ANSI A108.11, section 4.1 Wood Framing requirements. This section states all framing lumber should have a moisture content not in excess of 19%. Most pressure-treated lumber has moisture content ranges of 30% to 70%. In a tile assembly, pressure-treated wood as it starts to dry out has a tendency to twist and contort. The rigidity of the tile assembly cannot generally handle that type of movement and can fail.

In some areas, local building codes require pressure-treated lumber to be used when coming into contact with concrete. If this is the case, only the bottom 2×4 should be treated. Some of these codes may be under consideration for change.

Page 258 of the TCNA Handbook shows two industry-recognized construction details for shower curbs with a loose laid liner. One shows lathe and mortar over the liner, the other shows the use of a preformed curb. It is possible to use certain cementitious backer boards on the curb when constructing a pan with a surface-applied bonded waterproofing system.  TCNA Handbook methods B421 and B422 show use of an integrated bonding flange drain or a clamping drain and divot method. Both of these methods use surface-applied bonded waterproofing and a cement board covered curb could be considered with this type of system.  Some types of cementitious backer boards may be approved for this application, but first check with the respective manufacturer. 

NTCA Technical Team

DCOF on a pool deck

Question:

I’m designing a home and need to pick a tile for a residential pool deck. Are there standards for using slip-resistant tiles in areas like this, and if so, what are they?

Answer:

Thank you for contacting the NTCA, The measurements for slip-resistance are referred to as COF (Coefficient of Friction) and DCOF (Dynamic Coefficient of Friction). COF is the measurement of a tiles static frictional resistance, closely related to traction and slipperiness. DCOF is a measurement of dynamic friction, which is the frictional resistance one pushes against when already in motion.

Regarding the question of whether there is a specification or guidance for DCOF on a pool deck.  There is no specification or standard for slip resistance/DCOF/COF on a pool deck.  The reason is that each has its own unique design and use.  As such, it is up to the good communications process between the architect/specifier, owner, distributor, and installer to discuss and determine the best tile (type, glaze, traction, size, number of grout joints, etc.) for the installation being considered.

In addition, the tile and setting materials, membranes, expansion and movement joints, and other factors must all be carefully considered and approved or engineered for the application.

The NTCA Technical Team

What industry document supports installing stone over tile in a wet area?

QUESTION

I was curious if you could direct me to an industry document supporting the proper technique for installing Jerusalem limestone in a shower wall (stone over tile). The stone is 3/4” thick, and approximately 4’ x 5’. I don’t know the weight per foot. Can this be direct bonded or would it need mechanical fasteners? I’m looking for a document that would support one or the other.

ANSWER 1

When it comes to a large stone slab like this I need to direct you to the Natural Stone Institute (NSI) (naturalstoneinstitute.org). When 3/4” stone exceeds 24” on a side, it becomes outside the realm of typical tile installation and the NSI are the persons that best know how to handle this material. Their Dimension Stone Design Manual may address installing a slab over existing tile in a wet area, but I am not certain.

Adding mechanical fasteners may likely penetrate the waterproofing membrane, which can/will create problems with the system’s water management integrity. If the stone is not direct bonded with 95% coverage over the existing tile layer or membrane, any voids behind the stone may trap moisture, bleed through, and stain the stone (possibly permanently). NSI can speak to you about the suitability of limestone in a wet area. I am guessing this is a project you are involved with as the setting material manufacturer. You might want to advise the client that limestone can be a tricky stone for a wet area.

There are gauged porcelain tile panels (GPTP) that can be applied in a tile-over-tile, direct-bond situation without additional fasteners. You may want to suggest your client considers GPTP as an alternative. I can put you in contact with GPTP manufacturers/distributors if needed.

In the meantime, I am sure you know these things – but here are a few reminders for any tile-over-tile installations in a shower situation:

  • Ensure the existing tile installation/substrate is suitably well bonded, plumb, flat, etc., to support the new installation
  • Ensure the waterproofing membrane is intact or a new membrane is applied and connected to the pan
  • Take a look at TCNA Handbook methods TR418 and TR 420 for Shower Receptor Renovation details
  • Follow EJ-171 Movement Joint Guidelines

– Mark Heinlein, NTCA Technical Director

ANSWER 2

Here are a few more items for your consideration.

That slab of Jerusalem limestone would weigh approximately 205 lbs. dry and would increase when wet.

There are three classifications for limestone under ASTM C568 as follows:

  • Class I (low density) 7.5% to 12%
  • Class II (medium density) 3% to 7.5%
  • Class III (high density) up to 3%

The finish of the stone (normally honed) and the density of the stone will determine its porosity.

When it is installed in a wet environment (follow Mark’s advice on the installation), it should (must) be sealed using a breathable penetrating sealer per the manufacturer’s recommendations on the number of coats and dry time. Jerusalem limestone will require ongoing maintenance to keep it sealed and more easily cleaned. 

– Scott Carothers, Director of Certification and Training, CTEF

Should you soak encaustic tile?

QUESTION

I am a member and need a few questions answered about an encaustic cement tile installation. I only have about 35 sq. ft. installed, but the homeowner on a job insists I should have soaked the tiles prior to installation to create a proper bond. I am trying to check with the manufacturer for their recommendations but they are in the UK and I’ve had a delay due to time zone differences. The setting material manufacturer said that since the back of the tile was wet, they are confident it would be well adhered. Are there any standards for installing encaustic cement tiles? 

ANSWER

I don’t believe these tiles need to be soaked before installation. The best way to check bond to the substrate is to remove one to see how well it was adhered. Since the dealer does not have a comprehensive installation recommendation and this tile does not meet the ANSI A137.1 Standard Specification for Ceramic Tile, the decision on whether or not to soak the tiles prior to installation should be reviewed with the tile and setting material manufacturers. Request written installation instructions from each manufacturer along with their warranty on this project.

Understanding PVA/Polyvinyl Acetate

QUESTION

I need some help in understanding PVA/Polyvinyl Acetate. I understand contractors sometimes add PVA believing that it will strengthen the bond. However, in wet areas, PVA is known to re-emulsify and weaken the bond. Do you have any knowledge of PVA you can share with me, such as failures from using PVA as an admixture, and can you help me understand if there are any plausible reasons to add it to cementitious tile setting materials?

ANSWER 1

I am not a chemist, but in the past, there were two additives for thin-set mortars. One was the PVA you asked about and the other is an SBR (styrene butadiene rubber).

PVAs are used in glues like Elmer’s® and are water-soluble. Previously PVAs were used on some thin-set mortars but carried a disclaimer that they were for interior dry use only, and are seldom used any longer. SBRs are not water-soluble and can be used in exterior (wet) environments.

PVAs are generally less expensive than SBRs, but they are not created equal. 

I hope this is helpful. 
– Scott Carothers, CTEF

ANSWER 2

I reached out to some manufacturers and they were extremely helpful and sent me a lot of information. Following is a summary of this information: 

• PVA (polyvinyl acetate) not to be confused with polyvinyl alcohol is still commonly used as a general-purpose adhesive in interior or non-water immersed applications.

Frequently it is used as a bonding agent or primer prior to the application of non-modified plasters and mortars to a cementitious substrate. An attractive feature in this application is the “rewettable” nature of the bonding primer when it contacts the fresh alkaline mortar, allowing some inter-diffusion of the polymer that can help bind the new and old cementitious material together upon drying.

PVA also finds extensive use in wall jointing compounds for adhesion, binding, and flexibility, where water immersion is not a concern.

The issue that can arise from the use of PVA is that under wet/alkaline conditions, the vinyl acetate side groups will hydrolyze to hydroxyl functionality, which renders the polymer more soluble and prone to swelling and migration. That’s an advantage as a rewettable bonding primer, but a severe disadvantage for long-term moist environments as the adhesive effect is diminished.

In general, PVA is not used as a mortar modifier in the tile industry because it is likely to encounter wet and water-immersed conditions where the polymer’s adhesive performance would be severely degraded.

The tile industry as a whole relies heavily on the use of vinyl acetate-ethylene copolymers (VAE or EVA) for mortar modification. While the vinyl acetate group is still present, these polymers exhibit significantly improved resistance to hydrolysis due to the presence of ethylene on the backbone and in some cases other monomers. This resistance to the hydrolysis permits their use in wet areas and can meet the ANSI 118 standards that include water-immersed adhesion testing. This class of polymer is widely used in drymix, modified tile adhesives, and doesn’t suffer from the performance deficiencies of the PVAs.

It is possible to improve performance further through the use of other polymers such as styrene-butadiene, acrylic, and versatic chemistries, but these are typically at a price premium to the VAE’s and most valued in specialty applications where increased performance is a must-have and tolerant to the additional cost. The vast majority of tile adhesives function well using VAE polymers and they provide a good value point for most formulations and applications.  

• The first spray-dried polymer available was a PVA (polyvinyl acetate) homopolymer. You have been familiar with this polymer for years – Elmer’s Glue. The problem with straight PVA polymer is its sensitivity to water and instability in the highly alkaline environment of hydrating cement. By itself, even after the PVA polymer has coalesced (dried forming a continuous film), exposure to water or sufficient moisture can re-emulsify the polymer resulting in loss of bond. Also, in the very alkaline, high-pH environment of hydrating cement, the PVA polymer experiences hydrolysis, which breaks down the polymer into the original monomers. Hardly any manufacturers use straight PVA polymers in their products today. 

The second spray-dried polymer available was actually a copolymer (2). It consisted of PVA (polyvinyl acetate) with the addition of an ethylene monomer. This produced a copolymer that had two very good attributes. One, the PVA portion of the copolymer had very strong bonding characteristics. These bonding characteristics include an affinity to bond to cellulose (wood). Second, the addition of ethylene into the copolymer made it much more stable under the highly alkaline environment of hydrating cement. This product has become known in the industry as an EVA (Ethylene Vinyl Acetate) polymer. Since then, chemists were able to modify the performance characteristics of these polymers even more by adding additional monomers to the chain. Monomers such as vinyl versatate and vinyl laurate have been added to substantially increase the polymer’s resistance to water. All of these variations generate a wide assortment of polymers from which the setting materials manufacturers may choose. A polymer with more ethylene will impart more flexibility to the finished product than one with less ethylene if the polymers are blended with the same cement/polymer ratio. The manufacturer must determine what the desired performance characteristics of a product should be and then choose the proper polymer and cement/polymer ratio to put in the finished product to achieve their goals.

• Polyvinyl acetate is essentially Elmer’s Glue type material. When put into the high pH of cement, PVA will hydrolyze to form polyvinyl alcohol. This is not a good thing – because as you mentioned, the polymer re-disperses when wet and will adversely affect mortars.

To my understanding, typically, tile adhesive manufacturers do not sell or promote the use of PVA for ceramic tile installations. Most manufacturers will utilize alternate proprietary lattices or alternate chemistries that are stable in cement and provide all of the proven required characteristics (e.g. strength, flexibility, moisture resistance, freeze/thaw stability, etc.). 

– Mark Heinlein, 
NTCA Training Director

Using wall tile on a floor in a wet area

Question:

I am building a new home and learning things I never knew. One is regarding what tile can be put on a shower floor. I want a shower as in the attached inspiration photo. Apparently, they used a tile that is now discontinued. The new version I like is approved for a shower floor.  However, it is expensive and has divots/irregularities. I was hoping for something smoother and in budget.

Most black subway tile is not annotated as for shower floors. However, my sales representative is telling me that it is perfectly fine to use a wall tile on a shower floor. She is recommending a specific glazed ceramic wall tile 3×12 (black glossy).  Is she correct?

Answer – Part 1

Any tile considered for use in any application should have the manufacturer’s approval for the intended use. I suggest asking your distributor/salesperson to obtain the technical datasheet for the tile you are interested in. The TDS should specifically include information if the tile is acceptable for use on a floor in a wet area (such as a shower floor). If the TDS does not include this information, you can call the manufacturer directly to request this information or select a tile that is specifically rated for use on a shower floor.

Additionally, the durability of the tile in this application may or may not be affected by the type of shower pan being specified for this installation and its ability to properly support a soft-bodied wall tile.

Another consideration is the pattern and drainage system. If a running bond pattern is used (with a conical pitched floor to a center drain) it would result in lippage and accompanying puddling.  A running bond pattern with a linear drain system could help minimize any puddling. 

As you have discovered, tile is a complex science and art.  One of the most critical installations to construct is a shower. To ensure that you get all of the correct technical information you need for your installation, I strongly encourage you to employ an NTCA member contractor and a CTEF Certified Tile Installer. These contractors and installers own, understand, and apply the tile industry’s recognized standards, methods, best practices, and follow manufacturer instructions in the installations they construct. NTCA Members and CTEF CTI certified installers have direct unlimited access to the NTCA/CTEF technical team for training and detailed industry standards-based support in every installation they construct.

Please review the Ceramic Tile Education Foundation’s homeowner’s guide to hiring a qualified installer:  https://www.ceramictilefoundation.org/homeowners-guide-to-hiring-qualified-tile-installer

To find an NTCA member contractor in your area: https://www.tile-assn.com/search/custom.asp?id=2759

To find a CTI installer in your area:  https://www.ceramictilefoundation.org/find-certified-tile-installers

Question – Part 2 – 50% offset/lippage and saving money to cut large tiles into small tiles

Thank you so much for your help in my questions regarding shower tiles.  If you don’t mind, one other issue has arisen and I’d like to know the correct answer. It appears to my untrained eye that most 12″x24″ tile is laid so that each abuts the 2 adjacent tiles by 50% each. However, the sales associate said some governing body (Tile Layer’s Association??) had rules against that because of “lippage”?  Are there rules on how tile should be laid? If so, where is the resource for that? I’d like to know as being the homeowner, I assume I’m ultimately responsible for catching mistakes in the construction of my new home.

Also, is it better to purchase (at high cost) precut 4″x12″ or is it acceptable to have those cut by installers from 12″x24″?  A sales associate said the former is the better option.

Answer – Part 2 – 50% offset/lippage and saving money to cut large tiles into small tiles

These are excellent questions that are answered by the tile industry’s written standards and best practices.

It sounds like you are selecting a tile for a builder’s installer or tile contractor to the installer. I suggest asking your builder if their installer or contractor owns and applies the methods and standards in the Tile Council of North America Handbook for Ceramic, Glass and Stone Installation (TCNA Handbook), and the American National Standard Specifications for the Installation of Ceramic Tile.  These are the documents that answer your questions.

The associate you are working with is giving you solid advice based on these standards. The retailer you are working with is a strong supporter of NTCA and their staff and associates, many of which have attended our training programs, are knowledgeable about these things.

To answer your first question about the 50% offset for the 12×24 tile:

ANSI A108.02 Section 4.3.8.2 is where the answer is.  I will paraphrase what it says; When tiles with sides longer than 15” are being set with their long sides next to each other they shall be set in a pattern with an offset of 33% or less. If an offset more than 33% is desired (such as a 50% offset), the specifier and owner must approve a mock-up and agree to the lippage that may result from this type of pattern being installed.

The reason for this is that some tiles have what is called warpage as part of their manufacturing process. Warpage is when the tile is bowed in the middle. The ends of these tiles may be lower than in the middle of the tile.  When tiles longer than 15” are set next to each other in a 50% offset, this puts the high part of the middle of one tile directly opposite of the low part of the end of the adjacent tile. This can result in a difference in the height elevation of the plane between the two tiles.  This difference in the plane is known as lippage.  To quote the TCNA Handbook: “Lippage is a condition where one edge of a tile is higher than an adjacent tile, giving the finished surface an uneven appearance. Lippage is inherent in all ceramic installation methods and may also be unavoidable due to the tile tolerances, in accordance with ANSI A137.1”.

Not all tiles have warpage.  There are industry standards that describe acceptable warpage. Some tiles are made to meet those standards, some are not. The tile manufacturer can tell you if their tile meets the standard for warpage.  It is in ANSI A137.1.

Some manufacturers will have specific offset requirements for their tiles.  They may require a 20% or 25% maximum offset.

So, if you would like a 50% offset, you need to ask your tile contractor to lay them out or physically install a few so you can view them as they will look in the finished installation. At that time you would approve and accept (in writing) any lippage that occurs as a result of setting them at a 50% offset.  You will own and live with this installation – it is your decision to approve or reject the mockup.

To answer your second question about cutting 4×12 tiles out of 12×24 tiles:

The TCNA Handbook for Ceramic, Glass and Stone Tile Installation states:  Tiles should not be field-cut to size to accomplish modular patterns or to align grout joints, as field-cut edges will be dissimilar from factory edges and cannot be held to the same squareness tolerance.

This is not the desired practice.  In reality, it is not less expensive as your tile contractor should rightly be expected to charge labor and materials to cut down and smooth or hone the tiles. The tile contractor likely has excellent tools, but they may not be of the same grade as the tile factory and with human error, there may be variations from tile to tile after they are cut.  Expect the labor price will increase as more time is needed to ensure all tiles are well matched and finished.

Depending on the tile body and glaze, this practice may present an opportunity for chipped tiles. A large amount of additional tile may need to be purchased at the outset to account for this possibility.

For review:

As I mentioned in our last conversation, to ensure that you get all of the correct technical information you need for your installation, I strongly encourage you to employ an NTCA member contractor and a CTEF Certified Tile Installer. These contractors and installers own, understand, and apply the tile industry’s recognized standards, methods, best practices, and follow manufacturer instructions in the installations they construct.  NTCA Members and CTEF CTI certified installers have direct unlimited access to the NTCA/CTEF technical team for training and detailed industry standards-based support in every installation they construct.

Please refer to the links above.

I hope this information helps.

1 2 3 13