Ask the Experts – December


Here is the age-old question: Should I use caulk or grout to seal a toilet to a tile floor? Whatever is used will go halfway around the toilet. The goal is to protect the front of toilet from “fluids” and to prevent toilet from rocking. What do you recommend and why?


toilet_ATEToilets are designed to be removed and replaced. The tile floor is meant to be permanent. Toilets should not rock on a flat tile floor, but in the real world they often do rock. Most plumbers use wood or plastic shims to steady the installed toilet, and cut the shims with a utility knife so they do not protrude beyond the toilet base. Using grout or sealant to fill the space between tile floor and toilet base is your choice, though in my opinion, sealant is the much better choice. Grout, when cured, will not withstand the movement that will be present with toilet use, so cracks will develop. Also, grout has no water-resistant properties whatsoever. Sealants remain flexible, have sufficient bond strength and do give some water resistance. Be sure to use a sealant that meets ASTM-C920 performance stan- dards (like a 100% silicone) to get the longest-lasting sealant joint. — Michael Whistler, NTCA presenter/technical consultant


I have some tile and it has this statement on the packaging: “Please verify shade, calibre and grading. Claims regarding these items cannot be accepted after tile setting.” Can you tell me what shade, calibre and grading refer to?


boxlabel_ATEShading and calibre (also spelled caliber) refer to the color and size of the tiles, respectively. Each box of tile should be marked with its shade and caliber. Your job is to ensure that all boxes have the SAME shade and caliber before they are installed. If you use dif- ferent shades or calibers, you will be using tiles of different color and size – generally not pleasing to the eye. Every tile run has multiple cal- ibers and shade lots that are sorted and boxed at the factory, but it is possible to receive more than one caliber or shade within an order. You must check before installing so you can either mix the different lots together to avoid blocking, or reject the different lots and try to get all matching lots (which may or may not be possible). Grading is the designation on the label on each box that shows whether the tiles meet ANSI-A137.1 specifi cations (shown as “STD” or “standard”), or if the box contains lesser-quality seconds. – Michael Whistler, NTCA presenter/technical consultant

Ask the Experts – November

Our soap dishes fell off the tile tub surround, and were repaired by two different installers (using the term loosely). One was reset by using only grout to place it. The other was reset by punching a 2 1/2” to 3” hole in the green board and filling it with grout (not thinset) only. Are my concerns founded that now that the moisture barrier has been breached, the grout can wick moisture into the wall?

I dislike being the bearer of bad news, but there is probably no good way to re-attach those soap shelves. First, your tile was installed over a paper-covered gypsum product. Although common years ago, this method has not been allowed in wet areas for quite some time.

Second, tile and grout systems are not waterproof, or even water resistant. In fact, the tile system generally pulls water into the substrate (even if it is sealed). Over time, the paper on the gypsum board begins to degrade, and delaminate from the soft gypsum core below. Almost nothing will stick to this raw gypsum for long.

Not seeing the shower in person, I cannot unequivocally say that you are due for a new shower, but soap shelves falling off is usually the first sign of the end for this type of system. What usually follows is grout cracking and tiles falling off.  When these symptoms occur, you will generally find that in removing the old tile and green board there will be much degradation of the board, and likely mold, since the paper and gypsum in a wet, warm environment are perfect food for mold.

Michael K. Whistler, NTCA presenter/technical consultant

(from an architect)
Should I expect wall and floor grout lines to meet as best practice from a tile installer?

It is not a written industry standard that when using the same tile on walls and floors, or a modular tile (where more than one smaller tile plus grout joints equal the size of one large tile), all grout joints should align at vertical to horizontal tiled surfaces. Unless specified in contractual language, it is more a bonus of using a highly-skilled and quality-conscious contractor. This is the art of “layout” and can sometimes take nearly as long as the actual laying of the tile. There are times when it is physically impossible, as in the case where angled walls meet floors, but generally a quality craftsman will have nearly all grout joints aligned.

Michael K. Whistler, NTCA presenter/technical consultant

I was wondering what the best floor backer board is for porcelain and ceramic tile.

All the backer boards are good.  Each has different properties that may be needed for a specific project, such as thickness, dimensions of sheets available, ability to use on exteriors, weight, etc. Also keep in mind that if a cementitious backer board or unit (CBU) is specified for a project, substitutions are usually allowed with other brands of CBUs. But other TYPES of backer board, like foam, water-resistant faced gypsum, fiber cement or others will be difficult to substitute.  Not that any are bad, you just need to follow specifications.

So find a type you like, familiarize yourself with the manufacturer’s instructions and go to town!!

Michael K. Whistler, NTCA presenter/technical consultant

Ask the Experts – October 2013


I have a question about a new home constructed in 2012. We have porcelain tile over cement backer board over LP 3/4 floor decking. The backer board was installed with thinset to the OSB and screwed down. Tile was then thin set to the cement backer.

AtE-OctI have issues with loose tiles in two areas: kitchen and master bath. An engineer has assessed the I-joists and beams and found no movement or deflection. The contractor wants to blame the radiant floor heating, but I have hundreds of square feet of tile unaffected by the radiant heating. Any thoughts? Attached are a couple of interesting pictures.


Thank you for including the pictures. They make this an easy diagnosis. Your tile installer did not include movement accommodation joints (or insufficiently-sized joints) in your tile job.

Tile expands and contracts, and at a different rate from the substrate below. Every method shown in the TCNA Handbook for Ceramic, Glass and Stone Tile Installation requires movement accommodation joints. Interior dry areas need joints no more than 20’-25’ in each direction; exteriors, wet areas and interiors exposed to sunlight (i.e. where south-facing windows occur) 8’-12’ maximum. Glass tile and any radiant-heated tile need reduced distances, and in all areas, perimeter joints (where tile meets walls, cabinets or any dissimilar plane or surface) must be left open or filled with a flexible sealant. Even if the field distances are not exceeded, not including perimeter joints can cause this failure.

Many tile installers do not know the industry standards or have never experienced this failure, because it does not ALWAYS occur, but unfortunately for you, this is part of the learning curve for your installer. It generally does not take but one or two of these failures for an installer to learn the importance of including movement accommodation and spending the time up front to educate his clients (because there is generally an additional fee to perform this step within a tile project).

And please note that the thinset type is not a factor as long as it is suitable to tile and substrate. Even if there was a thinset that was 50 times stronger, the forces exerted by expansion cycling would still overcome it. Typically the thinset itself shears, but if it were stronger thinset, it would likely change the shear point to the substrate surface or the thinset/substrate interface.

The requirement to include movement accommodation joints is included in each installation method within the TCNA Handbook, and the specifics on placement and construction of joints is in section EJ-171. The TCNA Handbook is available on our website at for sale. It is really a standard that every tile installer should own.

Michael K. Whistler, NTCA presenter/
technical consultant

Ask the Experts – September 2013




I have been in a newly-built home for the last year. Upon possession of the home, air bubbles were noted in the grout. The tiler mixed new grout and applied it over the top of existing grout. After almost a year, cracks were discovered in the grout. Water presumably penetrated the grout cracks and allowed moisture behind the tiles and onto the mortar.

AtE_septThere was a secondary issue where only plywood was used and tiled over without a waterproof membrane. When attempting to rectify the cracks, the builder indicated that the cracks were due to the movement in the exterior wall from the settling of the home. Most of the grout was removed with a utility knife (therefore not completely removed). A couple of days later, a white crystal substance could be seen growing out of the grout lines. Thinking back, this was observed prior to the grout removal and was seen growing on the surface of the grout.

I wonder if you can provide any insight as to the cause of this growth, which I can only assume is efflorescence. As the manufacturer of similar products, I would be very interested in your opinion as to how to remedy the situation, and advice if you have ever heard of or seen such a reaction. It has been seven weeks since the grout was removed and it continued to produce this growth.


After looking at the pictures you sent, it appears that the tile was bonded directly to plywood walls with an organic adhesive (mastic). This is not an approved method according to The American National Standards Institute (ANSI) or The Tile Council of North America (TCNA)  for installing tile in a wet area such as a shower stall.

No tile or grout should be considered waterproof – even if a tile and grout sealer has been used. While some tiles such as porcelain are impervious and only absorb a small amount of water other ceramic tiles may absorb much more water – up to 30% of their weight. This absorption allows the water to transfer through to the back side of the tile, thereby requiring  a water management issue to be addressed. 100% waterproofing behind the tile is not required in all cases, but for a successful tile installation, a water-management system is required along with appropriate use of products.

For instance, a house with a shingled roof doesn’t have a waterproof roof. But if the appropriate shingled products are used, and a skilled professional properly installs these products according to ANSI standards or the product manufacturer’s written directions, a successful long-lasting installation will be achieved.

I’m sorry, but it appears necessary to remove all tile work in the wet areas and replace tiles using any of the several methods found in the TCNA Handbook for Ceramic, Glass and Stone Tile Installation for tile installation in shower receptors. Plywood and wet tile don’t mix well and will most likely continue to be problematic. This combination will most likely produce cracking grout joints and cracked or loose tile and also offers a perfect opportunity for mold and other bio-organic growth.

The National Tile Contractors Association (NTCA) web site offers a list of NTCA tile contractor members that are located all across the nation ( – click on Find a Tile Contractor or Consultant). I highly recommend a tile contractor that is a member of the NTCA, because members are well-informed on standards and updates in our industry.

– Gerald Sloan, NTCA presenter/consultant


Ask the Experts – August 2013


Oh my gosh! I inadvertently sprayed Lime-A-Way® on travertine! How do I correct the problem? Thank you for your professional advice.


You are definitely not the first person to say “oops” after spraying an unsuitable cleaner onto stone tile. It is actually a pretty easy fix, though probably not inexpensive.

You need to contact a stone restoration or stone re-polishing company. Try the Yellow Pages first, and if you don’t have a listing, call local tile distributors, local tile contractors, or local granite countertop fabricators, since this is a skill that some installation companies have. In some cases just the affected area can be ground and re-polished to blend indistinguishably with the surrounding original stone, but in some cases all the stone needs to be hit with the final grits to give an even appearance.

If this is a shower, all the better. Re-polishing stone done wet precludes the major dust that comes with dry grinding and dry polishing within your home. My company would have the polisher strip down to a pair of swim-trunks to do the wet polishing inside a shower, and once finished with the polishing process, wash down the shower and himself, and squeegee off the walls and shower glass.

Hope this helps.

Michael K. Whistler, presenter/technical consultant, NTCA



In the July 2013 Ask the Experts, the answer to this question was incorrectly stated, due to an assumption that the inquiry included concrete structures. This is the correct question and answer.


Can ceramic tile floor and wall finishes be installed in commercial modular buildings (which are constructed offsite, then hauled to and set up onsite) using the standard TCNA tiling methods, or are there special requirements for this type of building? These are wood-framed modular buildings (similar to those used for school classrooms), which would have restrooms with ceramic tile floor and walls. Are there any special tiling requirements to accommodate the movement of the manufactured building while being transported and set onsite? Maybe ceramic tile would not be a good choice here?


Any tile installation requires a certain stiffness, or lack of deflection. If in moving the structures it can be pre-determined or engineered that the completed tile installation will not be subject to any bending or twisting, it would probably work. I see this as highly unlikely, though.  Perhaps the structures could be moved into place and tile installed after the structures are permanently installed on their foundations.  Tile is a very good heavy-service finish, but it does require a very stable substrate.

– Michael K. Whistler, presenter/technical consultant

Ask the Experts – September 2012


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.


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.

I hope this information helps.

Gerald Sloan, NTCA trainer

Ask the Experts – August 2012


What is the best method to set and grout broken quarry tile (it may be called rip rap) to get smooth and grout-filled joints? I haven’t been satisfied with my foyers and patios.


It  sounds like you are changing your tile into a quasi-mosaic. First, your tile should be as lippage-free as possible – and as with all mosaic tile – you should use a beating block and rubber mallet to ensure flatness from one tile to the next. Second, when grouting, pack your grout fully into the joints, making sure to use correctly-mixed grout (don’t mix too wet). Wait until the grout will no longer transfer to your finger, then smooth your joints with a well-wrung sponge. Last, try dragging a large cotton (or better, wool) towel over the tile as your final wash.

Michael Whistler, NTCA Trainer


A contractor put an outdoor patio in for me using quarry tile. In the contract he stated that he would do the work according to the industry standards. He put the quarry tile down on top of packed chad. Packed chad is also called minus: it’s the chip and small pieces of rock left in the rock crushing process, used for roads and landscaping because it packs down. It is crushed rock along with all the very fine particles created during the crushing process.

The mortar will not stay in and I am told that it is because the tile should have been set on at least 2” of concrete. The contractor is not doing anything to correct the problem and it looks like I am going to have to take him to court to get this resolved. In order to prove a case against him for a breach of contract, I am going to need a document stating the ANSI standard for laying quarry tile outside. How and where can I go about getting these documents?


There is no approved TCNA or ANSI method to install tile over “packed chad,”  or “minus.” There are approved masonry methods for installing pavers and brick over packed-sand beds. But pavers and brick are substantially thicker than tile, usually 2”–2-1/2.”

I would expect you are getting cracked grout joints because this tile has been installed over a substrate that will move due to point-load stresses on the surface of the tile above.

I am sorry you are having this failure, and recommend you get in touch with one of our Five Star Contractors ( or NTCA Member Contractors ( in your area. NTCA members typically have more knowledge than the average tile contractor. Enter the URLs above or go to and click on the tab to “Find a Contractor.”

The one sunny spot in this situation is that if your tiles were dry-laid over this “packed chad,” you will more than likely be able to reuse them for a proper installation. When you remove them it should be relatively easy to knock the grout off the edges (if it is cementitious grout) and use them a second time.

Michael Whistler, NTCA Trainer

Ask the Experts – July 2012


I’m looking for a technical answer to my question as soon as possible. Please tell me the standard procedure for installing tile in an elevator. Are technical advisories available?


This is a commonly-asked question due to potential risk involved when installing tile in elevator floors.

The most important step prior to the tile installation is to determine if the elevator cab was designed to accommodate tile as a finish floor material – most often they are not designed for floor finishes that include tile or stone but are designed for other finishes such as carpet or vinyl. This is due to the extra expense required to stiffen up the substructure to make it strong enough not to deflect or bend excessively under maximum load capacity. This added expense can be between $5,000 to over $10,000 and is usually why the design professional is often forced to choose the less-expensive alternative.

The tile contractor should consult the general contractor, architect, or the design professional responsible for the elevator cab to find out whether or not tile is listed as an accepted floor finish product. Many tile contractors have installed tile or stone in elevators that were not designed for such and found themselves trying to repair broken tiles and cracked grout joints, only to have an ongoing issue due to excessive substrate deflection.

If the elevator cab floor has been properly designed and has tile or natural stone listed as an acceptable finish, there are several commonly used methods available such as: direct bond the tile to the elevator cab floor using epoxies; using a scrim-faced, crack-isolation membrane bonded to the substructure with a primer material or a highly modified tile-setting thin-set material; or 2.5 galvanized wire lath with stainless steel mechanical fasteners/screws then skim-coated with highly-modified thinset and direct-bonded to the wire lath.

None of the methods are found in the ANSI or in the TCNA Handbook. As always, follow the product manufacturer’s directions for the products chosen. Complete warranted systems are available from several setting-material and crack-isolation membrane manufacturers.

– Gerald Sloan, NTCA presenter and trainer 

Ask the Experts – June 2012


I am a new member of the NTCA and I have an upcoming small project that I need help with.

I do mostly interior residential remodeling. Tile is probably 60% of my projects. I have a client with a concrete porch he would like tiled. The problem is the broom finish has been sealed with an “oil-based” sealer he purchased and applied himself from Lowe’s. As the broom finish is quite deep I don’t think it could be ground down. I can’t find anything in my TCNA Handbook that addresses this.


This is a good question. Many contractors fail to determine that a substrate has been sealed and end up with problems down the road. Both TCNA Handbook methods and ANSI require that a substrate be free of contaminants, curing compounds and sealers. Exterior tilework, which requires the highest performance level of any type of tile installation, requires the best bond, as well as 95% mortar coverage and appropriate movement accommodation. Any sealer on a substrate will act as a de-bonding agent, and give less-than-optimum bonding ability.

You may want to call the technical department of the mortar manufacturer that you want to use and ask them, but I believe they will give you the same answer that is in the TCNA Handbook and ANSI, that you must mechanically scarify the concrete (grind or shotblast) until the contaminant is removed and you have a clean surface to install tile over. Any other method is risking a potential failure.

On your concern that the broom finish is too deep to grind, there are some very aggressive grinders with vacuum attachments available that can cut quickly and in a dust-free fashion.

– Michael Whistler, NTCA Tile & Stone Symposium presenter and trainer

Ask the Experts – May 2012


What is the standard installation for ceramic tiles on Gyp-Crete®? The floor consists of light-gauge metal framing, with ¾” plywood subfloor and 1” Gyp-Crete. Preparation of the Gyp-Crete consist of the application of sealer prior to the installation of the tiles. Would this floor be adequate to receive ceramic floor tiles?


I am concerned with your statement regarding lightweight metal joists. The floor must be engineered to support dead and live loads, and tile can be heavier than most other floor coverings.

You also state that you want to seal the Gyp-Crete. Instead, you need to prime the Gyp-Crete with the primer that your mortar manufacturer recommends.

You should also follow the installation instructions that are provided by the specific manufacturer of the gypsum underlayment you are using.

Also be advised that Portland cement and gypsum can have an adverse reaction if placed contiguous to one another, which could result in a possible loss of bond. To alleviate this risk, many tile professionals always use a waterproof/crack isolation membrane or uncoupling membrane between the gypsum and the tile.

Michael Whistler,
NTCA Tile & Stone Symposium presenter/technical consultant



I am installing floor tile for a client. I have contacted the manufacturer, which has ultimately brought me to this email. I need to find out what the relative humidity of the concrete slab should be (ASTM F2170) prior to the installation of this tile.


Typically moisture testing is done with a calcium chloride test kit, which measures how many lbs. of moisture per 1000 square feet are escaping the slab in a 24-hour period. Anything less than 5 lbs. per 1000 is probably suitable for use with cementitious mortars. Anything more than 5 lbs., you should contact the mortar manufacturer to ascertain suitability of their product with high-moisture slabs. Any slab measuring 12 lbs. or more per 1000 needs special consideration, and possibly a moisture barrier, depending on manufacturer’s instructions.

Michael Whistler,
NTCA Tile & Stone Symposium presenter/technical consultant

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