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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

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.

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

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.

Waterproofing for exterior balcony

QUESTION

I have a customer with an exterior balcony that is tiled on the floor and walls. The space below the balcony is conditioned space (front hall). The waterproofing has failed and he’s getting water in the room below when there’s rain. I don’t know what the existing waterproofing system is. He has asked me to remove and replace everything, but I’m not sure what kind of substrate/waterproofing to use. The rep of the company whose products I usually use tells me that they’re not approved for exterior use. The balcony has walls on four sides, so I need to be able to incorporate drains to let the water out. Is there a product that you can recommend for this application?

ANSWER

I am glad you have asked questions about this installation before proceeding. An exterior balcony over occupied space is among the most critical types of installations a tile contractor can face. There is very much information to consider, more than can be addressed here, so I will begin by listing the applicable reference material and asking you to take a look through the information listed below.

TCNA Handbook (2019 Edition)

  • Wet Areas Guidelines (Page 41)
  • Environmental Exposure Classifications (Page 44). See the definition for Res6 (Residential Exterior) and the charts for Floors and Walls on pages 46 and 47.
  • Methods for Exterior Roof/Deck and Balcony/Deck Floors: F103; F103B; F104; F105 (Pages 60 – 67).
  • Methods for Exterior Walls: W201 (Page 186); W202E (Page 188); W244E (Page 190)
  • EJ171 Movement Joint Guidelines for Ceramic, Glass, and Stone (Page 430)
  • Appendix B. Estimated Weights for Floor Installations (Page 444)

When reviewing the TCNA Handbook methods for Exterior Roof/Deck and Balcony/Deck Floors that I’ve listed above, please make note of this statement in the Preparation By Other Trades section: “Roof drains and membrane by other trades – provide completed drainage at roof membrane level by use of weep holes as shown or other methods.”

Regarding movement joints, please note of the Movement Joint section states: “…architect must specify type of joint and show location and details on drawings” and Method EJ171 states: “Because of the limitless conditions and structural systems on which tile can be installed, the design professional or engineer shall show the specific location and details of movement joints on project drawings.”

ANSI A108 / A118 / A136 (July 2019 Release date)

  • There are multiple sections in A108 and A118 that pertain to exterior and wet area installations, movement joints, thick bed system requirements, etc.

NTCA Reference Manual (2019/2020 Edition)

  • Prerequisites and Considerations for Successful Balconies, Courtyards, Patios, Plaza Decks, Roofs, Exterior Walking Surfaces and Swimming Pool Decks (Pages 156 – 157)

The section I’ve noted in the NTCA Reference Manual is extremely informational – please read it first. At the end of that section you will read this: “DISCLAIMER: The tile contractor is not responsible for the design of the system. To avoid potential liabilities use a general contractor and certified roofing contractor when waterproofing over occupied living space.”

There is no simple product recommendation or set of instructions or solution I can offer. The best advice I can give you is:

  • Follow the guidance of the NTCA Reference Manual and the TCNA Handbook, which recommend employing a general contractor, architect, structural engineer as needed to properly design and specify the structural support; mechanical (drainage) systems; movement/expansion details; waterproofing system and other elements of this very complex installation.
  • Hire a roofing contractor and mechanical contractor to install the primary roofing membrane and the mechanical/drain-waste-vent system.
  • Ensure considerations are made for any railings/balusters to not puncture the primary waterproofing layer unless they can be adequately sealed.
  • Ensure all of the waterproofing and membranes are flashed onto the walls and – since the walls are being tiled – are fully waterproofed or the water managed as outlined in the wall methods I’ve listed.
  • After the project has been engineered and designed by structural and mechanical professionals, contact and involve setting material and membrane manufacturers that will assist you in product selection and ask them to provide you detailed installation instructions for their products and a written system warranty that covers their products in this installation.
  • Follow all manufacturer instructions and guidelines in the TCNA Handbook, ANSI A108 and the NTCA Reference Manual.
  • Clearly communicate the complexity of this project to the homeowner and inform them what it will take to ensure their project is a success.

I hope this gets you started. After reviewing this information please contact me again with any questions you might still have and I will help as best I can. 

Who determines construction joints?

QUESTION

We are on a job won by a flooring contractor who will install sheet vinyl or porcelain tile on a concrete floor. We are trying to determine who identifies where the construction joints are and how they will be treated, if it is not provided in the drawings.

ANSWER

The person with knowledge of the building and structure has to identify where the joints are and how they will be honored or treated depending on the type of joint. 

If there are drawings and specifications for the job, the professional that analyzed the structure to ensure adequacy for a tile installation and who drew up the specifications is the person responsible for providing the tile installation contractor the drawings for location and identification of honoring / treating the structural joints.

You can refer them to TCNA Handbook method EJ-171 where this is further defined. 

Thin brick tips

QUESTION

Thin brick veneer is a popular option because of its light weight and cost.

I am bidding 10,000 to 12,000 square feet of thin brick. And I thought some advice would be prudent!

Would you care to share with me some of the tips and methods you put together? Any advice would be very much appreciated!

ANSWER

The NTCA Reference Manual has an upcoming white paper that deals with grouting thin brick; I will highlight some of those upcoming best practices.

If your project is in an interior dry location, then a standard grout (ANSI 118.6) or a Type S or N mortar may be acceptable, depending upon the environment it’s exposed to. (Please see the Environmental Exposure Classifications page in your TCNA Handbook).

However, since you have said that it is 10,000+ square feet, I am basing the following comments on the assumption that this project will be on an exterior wall location. When grouting thin brick in an exterior environment, installations using a standard cement grout (ANSI 118.6) or a Type S or N mortar have had their share of problems. These types of grout/mortars are easier to install using a grout bag with metal tips and they usually give the installer extended time to tool the joints. The problems are revealed when these installations are exposed to rain or freeze/thaw situations. These problems include the likelihood of efflorescence in wet areas and spalling in freeze/thaw applications. So for these reasons, standard cement grouts and mortars are not the “best” practice when it comes to grouting thin brick.

High-performance grout (ANSI118.7) is typically recommended by setting material manufacturers to minimize efflorescence and block water penetration into and through the grout. Installing these types of grouts has challenges, however, when they’re being used with typical wire cut (rough texture) thin brick.

These grouts usually use rapid-curing cement that gives the grout its high-performance characteristics, but these same qualities make them exceptionally difficult to clean from the face of the bricks. Additionally, the stiff texture and rapid setting of many high-performance grouts don’t lend themselves to being installed with a grout bag. If you soften the grout up by adding additional water to make bagging easier, you weaken the grout and it typically won’t stay in the joint, sagging onto the face of the brick, resulting in the problem you are trying to avoid by using a grout bag – getting grout on the face of the brick. Then you have to scrub the brick to try to clean it, many times resulting in low joints. 

Some contractors have found it helpful to use grout release (sometimes multiple coats are necessary), penetrating sealers, or even applying a sacrificial wax coating prior to installing the thin brick to reduce the absorption of the brick prior to grouting. 

However, each of these methods still has its own costs and challenges. Many will require an acidic type of cleaner and/or pressure washing. And the sacrificial wax coating will need to be removed after grouting and curing is complete by using a hot-water, high-pressure washer.

In view of these many challenges, it is always to your advantage to do a mock up prior to starting the job, as well as working with a setting material manufacturer and using its complete system (usually membrane, thinset, and grout), and consulting the thin brick manufacturer for its recommendations as well. Also ask your grout supplier if using one of their liquid admix products will give you the fluspeffy texture you’re looking for, since in certain grouts they’ve helped.

Some specifications for jobs that I have done require the grouting to be installed using a grout bag and others don’t. Therefore, some tile contractors qualify their bid to include their proposed method for installing the grout, joint treatment/tooling and cleaning method –including that while the face of the brick will be cleaned, the pits in the face of the brick may still contain some residual grout in them after final cleaning.

Hopefully this is some help, if you have any additional questions please feel free to email or call.

Thank you for your support of the NTCA.

Discoloration on shower grout

QUESTION

Any chance you’ve seen discoloration on grout that’s brownish red? I have a few theories, but I honestly, never seen anything quite as grungy as the discoloration on this client’s shower.  

ANSWER

Sometimes mold that appears on grout is superficial and resides only on the surface of the installation. Most shampoos and soaps contain organic matter, some more than others. When you have organic materials, temperatures and moisture, you have a great environment for mold to grow. Proper and regular cleaning of showers removes those materials. When used and not cleaned regularly you can end up with a “grungy” situation. Always use a neutral pH cleaner approved for cleaning the stone or tile in your shower. And always test them in an inconspicuous area to make sure you will have no adverse reactions. Double check for mold or wet areas outside the shower as well to ensure there are no leaks. If water has escaped the shower assembly and has reached the wood substructure this can also provide the organic matter needed for mold to grow.

Efflorescence reappearing on stone floor

Question:

We just installed a stone tile shower floor. It was sealed twice and shortly after white stuff kept showing on the floor even though the walls of the shower and the bathroom are of the same tile. We then removed the sealant and re-sealed it. Again shortly after this white stuff comes out. I have used an efflorescence cleaner which removed it, but the white stuff keeps coming back. Can you tell me what is happening and how we can fix it?

Thank you in advance for all your help.

Answer:

Without being there on site and doing several destructive tests to determine the actual cause of the problem, I can give you several of the most common causes for the condition that you have described. First of all, given the cleaning product you have described, it sounds like soluble-salt efflorescence. This soluble salt is a natural product that is present in the Portland cement-based products used most often to produce the setting bed that is under the tile installation and the grout material that is used to fill the grout joints.

Natural stone tile may contain these mineral salts as well, especially if the natural stone is a softer material such as marble or limestone. These mineral salts may, and most often do, migrate when exposed to water or water vapor. As a way to control or minimize this efflorescence, water management is of the utmost importance. Careful consideration of the materials being used should be taken into account. Efflorescence that occurs after the tile or stone installation is in service is very difficult to stop or even control. Time and use will eventually cause all the “free mineral salts” to be exhausted and the problem will go away, but to fix this problem from the beginning will most likely require a removal of the entire shower floor, and may even require removal of portions of the walls or all the walls as well.

Starting fresh with a new shower framed and ready for tile or natural stone, the methods for proper shower assemblies can be found in the TCNA Handbook for Ceramic, Glass and Stone Tile Installation. These methods show pre-sloped shower pan assemblies, weep hole protectors, references to American National Standards Institute (ANSI) for proper mixes and measures for setting beds such as 1-to-4-ratio of Portland cement to washed masonry sand used in many shower pan assemblies. The TCNA list cautions when using soft natural stone products in wet areas – if efflorescence may be of concern – a porcelain or ceramic tile that is made to resemble natural stone may be a safer choice.

A few things the NTCA Reference Manual has to say about the causes efflorescence are as follows:

  • Soluble salts from the Portland cement-based products brought to the surface by capillary action where there is water or moisture present.
  • Contaminated water or sand containing soluble salts.
  • Excessive mineral content in the water used for maintenance.
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