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

Ask the Experts – Coverings 2012 edition


What is the association’s recommendation as far as a trowel size to use when installing an 18”x18”x3/8” ceramic tile? Do I need to back-butter the tile? I am installing on 1/4” Durock placed over 3/4” plywood subfloor over radiant heat.


For an 18”x18” tile, you should use a medium-bed thin-set mortar. You will probably need a 5/8”x3/4” loop-notch trowel to get the proper 80% coverage for interior dry areas. Back-buttering is always a good idea to improve coverage.

– Michael Whistler, NTCA Symposium presenter


We need an installation method for installing Daltile 2”x2” mosaic tile in a roll-in shower room. The architect has had us use a cleavage membrane (#15 felt with wire lath) at all floor areas where we’re using mud. The building floors are a concrete plank. There is also a drain outside of the shower area in the space where the toilet and sink are. The rooms outside the shower will get wood flooring with wood sleepers below (approximately 2” total). There is no need for a saddle between the shower and the toilet and sink area. The high points should be around the perimeter of both areas, and most importantly at the entry into the shower area, which acts as the high point for both areas. We would use waterproofing. What do you suggest?


To follow is a drawing that shows common installation procedures for curb-less shower systems to retrofit an existing shower with ADA-approved wheelchair accessibility. No saddle or threshold that a wheelchari need negotiate will have a change in elevation of more than 1/2”, and no two elevations shall occur closer than 5’.
This can be used with a cleavage membrane along with reinforcing wire but will increase the mud bed thickness from 1/2” to at least 3/4” at the thinnest locations for residential; 1-1/4” for commercial. This may require raising the floor outside the shower 1/4” to 3/8” to meet the wheelchair accessibility recommendations. This is a common practice but is not yet available in the TCNA Handbook. The NTCA Methods and Standards Committee is currently working on submissions related to barrier-free and curbless showers for the Handbook.

– Gerald Sloan, NTCA training director

Is the installer responsible for damages?


If a tile installer damages things in my home, should he fix them? As a result of this tile installer’s sloppy work, my arcadia door (where the tile comes up to) now drags and squeaks. Before installation, no problems, for 20 years. He also scraped the metal track of the door so now I have to paint the metal. He told me I could take care of both of these things myself. Shouldn’t he????


This is a fair question, and addresses whether you have a quality contractor. I assume the door now rubs and squeaks because the new tile is higher than the old flooring, so the door now scrapes along its bottom. This is an issue that needed to be discussed and decided before work commenced. Most companies will seldom modify doors, but there are times when the contractor should subcontract a carpenter to cut the bottom of a door (if the door is wood). This should always be discussed during bid time, so the client knows ahead of time there might be an additional expense.

As far as damage to other finishes, the contractor should always repair or fix things they mess up. Reputation, customer satisfaction and ethical dealings should be of utmost importance.

Ask the Experts – March 2012


What is the best way to handle a situation with a general contractor (GC) on a job I am just starting? I remember from the NTCA Symposium you had some good points on how to deal with incorrect specs and GC’s.

It is on above-ground concrete (steel framing and decking) with 1/4˝ deep saw-cut joints cut every 10’ or  so. I recommend a full coverage membrane installation over the saw-cut joints; GC wants to go partial to save money. Tile will be 16˝x32˝ porcelain.


This is a good question, and begs some questions from my end. Do you want to use an anti-fracture membrane so you can offset movement joints away from their current positions? Are you hoping to be able to eliminate some of the joints by using the membrane? Is this installation a running bond or is it a square grid pattern?

There is new industry language re: above-ground concrete that says you should revert to the more stringent 10´ to 12´ maximum distance between movement joints, so maybe your saw-cut joints should just be followed up through the tile. There’s also language that says you should never cover any type of construction joint, including saw-cut joints. Any joints in the substrate should follow up directly through the tilework with a soft/movement joint above. If you decide to offset or ignore these joints, you will definitely be taking a large risk.

I took a firm stance after a couple of failures. I gave documentation showing that soft joints were industry requirements, and tried to educate the owner, design pro or GC that the tilework needed room to move. If we came to loggerheads on the issue, I would not proceed until I had direction, IN WRITING, to do the tile installation against industry and my standards. But realize that even with such a document, you are still at risk. In the event of a failure, the court will rule against you saying that as the professional you should have known better.

– Michael Whistler, NTCA Symposium presenter

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