April 25, 2015

Ask the Experts – March 2015

SponsoredbyLaticreteQUESTION

I am reaching out to you because the electric floor heating installation instructions of the system I am about to install listed you as a source for technical advice. I am about to install a cable system, and according to their installation instructions, they say to put down either cork underlayment or anti-fracture membrane prior to installing the wire. This makes sense to me for heat distribution up rather than down. I don’t see how I can just lay cork on the floor and tile over it.

suntouch-heated-floorAs far as the anti-fracture membrane, other manufacturers say to put the heating wire under the mat. That seems to defeat the purpose of putting anything down for insulation. This is a 60+ year old floor, no cracks; so barring an earthquake, I don’t foresee any cracks starting now. Could I have your views on this please?

ANSWER

Floor-warming systems generally work way more efficiently if you incorporate a “thermal break” to stop a good portion of the heat from radiating downward into the substrate. Cork or foam building panels are all used as this thermal break beneath the heating element. Follow manufacturer installation instructions to properly install these products over your substrate.

Michael Whistler, NTCA presenter

QUESTION

I have a question regarding the installation of a porcelain tile floor using 12” x 12” tiles. The room size of the kitchen is 23′ x 13′.

We have 24″ on-center (OC) trusses, which are known for flex. We currently have 3/4” plywood nailed to the trusses.

I need to know what is required for additional subflooring to prevent the tile and grout from cracking because of the flex.

From research I have done online, I have come up with varying opinions, but all seem to point in the direction that additional plywood is required before the cement board.

If specs could be sent, it would be greatly appreciated.

ANSWER

There are actually six methods in the 2014 TCNA Handbook of Ceramic, Glass and Stone Tile Installation that show allowable 24” OC installations. Five involve the use of a secondary layer of plywood, one shows uncoupling membrane and one shows coated glass mat water resistant gypsum backerboard.

There are also numerous backerboard and tile substrate manufacturers that allow and warranty their products over 24” OC if used in accordance with their installation instructions.

The NTCA always recommends that you contact the manufacturer of the products you intend (or would like) to use and procure a written warranty. We also highly recommend that you have and read the TCNA Handbook before proceeding in order to acquaint yourself with all the issues involved and to ensure a successful installation.

Michael Whistler, NTCA presenter

Ask the Experts – February 2015

SponsoredbyLaticreteIn November 2014, TileLetter published the story, “Stacking the deck: manufactured/natural stone veneers pros and cons,” on page 54. Later that same month, this question about installing brick veneer came in from an NTCA member:

QUESTION

Hello – I’m an existing NTCA member, with a question about an upcoming project involving brick veneer.

Does method W243 – 14 apply to brick veneer, and if so, is it applicable in a basement environment? Are there any limitations as to when or where this method can’t/shouldn’t be used?

veneer_paver_tilesANSWER

The method W 243 – 14 that is referred to in the TCNA Handbook for Ceramic, Glass and Stone Tile Installation is a suitable installation method for installing “thin” veneer brick paver tiles but not an acceptable method for “full thickness “ brick veneer installations. “Thin” is typically 5/8” thickness or less. This direct-bond method is only applicable due to weight-pounds per square foot dead load applied to substructure including the facial surface of the gypsum backer unit .

Full thickness brick veneer is much too heavy to direct bond to a gypsum backing unit using this method.

Limitations are listed in the method, such as environmental temperatures not to exceed 125 degrees F and stud spacing not to exceed 16” on center.

Gerald Sloan, NTCA trainer

Our second dialogue concerns a question of replacing grout or the entire floor that was damaged as a result of a flooding situation. Expert response by industry consultant David Gobis helped this homeowner settle the matter with her insurance company.

QUESTION

My kitchen floor is tile that is about 10 years old. We recently had new countertops installed along with a backsplash. We kept the tile floors because they were in beautiful condition. On January 8th, 2014, a second-floor bathroom pipe froze and burst onto our kitchen tile floor. That water sat in an area for about 6-8 hours. Now we have tile that clicks and grout that is coming up in the area where the water sat. The insurance company wants to just re-grout the area and not do anything with the loose tiles. My husband and I have had tile experts to the house who would not recommend just patching the grout since the tile is no longer attached to the board underneath. Please email me your thoughts.

ANSWER

Grout will not fix a floor that clicks, which is likely the wooden panel riding up and down a nail. With a flood, the water works its way through the grout and becomes trapped in the supporting wood structure under the tile. With most tile having a glazed (glass-like surface) it takes a long time to dry out. That causes the wood to change dimension by swelling, often breaking the tile or cracking the grout. While it is possible a regrout will help  the problem, it is not likely. I would let them try their grout fix offer with the caveat that if it does not work  they will look at replacement – and I would ask for it in writing.

David M. Gobis CTC CSI, Ceramic Tile Consultant

RESPONSE

Since your last email I just wanted you to know that the insurance company did come to our home along with a tile expert. And what you said is the same thing that the tile expert said. So we have had a new tile floor installed in the kitchen to replace the damaged one.

BONUS QUESTION:

You answer it!

We received this technical question – what is YOUR opinion about who is the responsible party for this job – the licensed contractor? The first unlicensed contractor to grout the floor – or the last? Send responses to lesley@tile-assn.com.

If an installer installs a tile floor and a second installer grouts the floor but then a third installer removes that grout and re-grouts the floor who is responsible for the floor? The original floor was installed (no grout) by a licensed contractor, grout was done by an unlicensed individual hired by the homeowner, and then a third individual was hired by homeowner to remove the grout and re- grout.  The individuals doing the grouting were independent and not working for the original company.

Ask the Experts – January 2015

SponsoredbyLaticreteThis month’s conversation is between a knowledgeable female do-it-yourself tile setter and Dave Gobis, CTC CSI Ceramic Tile Consultant. It illustrates the vast amount of misinformation that’s passing as expertise at point-of-sale. It’s a classic tale of buyer beware, and know-your-stuff.

QUESTION

My shower is almost complete, having installed my cement boards over a wood structure covered with plastic sheeting. I have used 100% silicone to seal all joints including those between the cement boards and my mortar bed. I am also going to waterproof all the cement boards with a waterproofing membrane. I know I’m supposed to use latex thinset for the floor. What kind of mortar do I use to install the tiles on the walls of my shower? As per the TCNA, I’m supposed to use latex thinset for the walls as well but a tile dealer I work with has told me that I can’t use latex-modified thinset for my walls because it will take three months to cure on account of the plastic I put on my wood structure. I would be much obliged for your help. Thank you.

ANSWER

Your tile dealer is misinformed. Your waterproofing membrane would be even less permeable than the plastic which has holes in it from fastening the board. There is truth that a longer drying period is required when installing tile with latex over a waterproof membrane. The thinset will use about a third of the water for mixing the thinset in growing a cement matrix, the rest will have to evaporate through the grout joints. Leave the joints open a few days before grouting and you will be fine. Cement grout is porous and will allow any residual moisture to pass if needed.

– David M. Gobis CTC CSI
Ceramic Tile Consultant

QUESTION

Thank you for your reply on the latex thinset; I just didn’t know who else to turn to and was getting exhausted with the different input I was getting from my tile suppliers.

In the same vein, should I wait three months to install glass doors on my curb tiles? Not that I mind; if I have to wait, I will. Furthermore, if I have to wait weeks to grout, I won’t mind either. At this point, being so close to finishing, I don’t want to mess up anything.

ANSWER

What was the reason for waiting three months on the shower door? Have never heard anything remotely close to that. Biggest thing is to not puncture the waterproofing. If you could let the tile set up for a week to 10 days that would be good enough.

– David M. Gobis CTC CSI
Ceramic Tile Consultant

QUESTION

You’ve just answered all my questions. The three-month cure time was told to me by one of the two tile stores I bought my tiles from. Based on that information, I started asking myself about the glass shower doors on the curb. Such is the nightmare of having no experience! Thank you so much for your prompt answers. Have a great one.

ANSWER

The misinformation out there is abundant. It’s sad that people know so little about their chosen line of work. It certainly keeps me busy, but it’s a hard way to make a living when all you sell is what you know. The tile setter I was with when I got your three-month email chuckled and said something about a knucklehead.

– Good Luck, Dave

QUESTION

I’ve been doing my own tile work for 20 years, but had never undertaken a shower from drain pipe to shower head. It became clear to me as well that misinformation was rampant, even amongst the professionals showing how to do it on YouTube. I could not get proper instructions on the internet or YouTube until I got hold of the ANSI code and the TCNA instructions. Even if you do decide to follow the code, as I decided to do, most stores don’t know the code and/or don’t follow it which has made my project that much more difficult as products are not always available. I feel like I’m speaking a foreign language to these people. You should’ve seen the hardware store reps when I asked for wet sand. Not to mention that some of these reps have tried to sell me gypsum or thin cement boards (3/8”) for my shower walls. One of these reps at a big box store actually told me – with Oatey pan liner package in hand – that I didn’t have to do a mortar bed after putting my PVC pan liner on my pre-pitch; I could put the tiles directly on my PVC pan liner and save myself the trouble of doing a mortar bed (!?!?). He even said, with certainty, that this was up to code (after I told him it wasn’t).

Tell your tile setter that he is right; knucklehead it is. Now, all I have to do is go back to the knucklehead and put in a special order for my latex thinset because they don’t carry these products in their stock room.

Again, Dave, much obliged.  I will sleep better tonight knowing that I now have the proper information.

Ask the Experts – December 2014

SponsoredbyLaticreteQUESTION

Dave, I came across your article The Importance of Using Expansion Joints this morning. I’m tiling (porcelain) a good size interior room (~15’ x 44’) with staggered, plank-style tile in the long direction. According to the TCNA Handbook, I should have at least one movement joint. However, with this layout I would need to terminate the tile runs somewhere in the middle to lay in a straight movement joint across the width of the room, breaking up the flow of the tile.

I have not come across any solutions to this aesthetic problem. With perimeter spacing, limited temperature variation, and no direct sunlight, I’m tempted to skip the movement joint.

Any suggestions?

1-ATE_1114ANSWER

Expansion joints have always been a battle; nobody wants them and installers don’t want the extra work that they know will result in complaints about appearance if they do put them in. Early in my career I ignored them and felt they were not necessary. Having a fixed place of business for over 20 years and hourly employees, that came back to haunt me. Anyone could find me whenever they so desired, and when they had problems they did.

The lesson learned was we either put movement joints in or have someone sign a form letter saying they chose to ignore our advice and not to have them installed. Some were offended, and others chose to sign. It was never a good feeling either way when we encountered resistance.

The value of expansion joints – also known as movement accommodation joints – is not realized for years after the installation. It doesn’t matter what part of the country you live in, including Hawaii. Tile expands and contracts with changes in temperature. Tile expands on a limited long-term basis and does not contract with exposure to moisture, be it water or vapor.

2-ATE_1214Concrete experiences endless shrinkage and wants to curl, in addition to the tile properties. Keep in mind the tile is getting bigger while the slab is getting smaller. Concrete slabs without effective vapor barriers experience a high degree of vapor transmission. We commonly receive calls about tile tenting after big storms. Wood structures experience endless dimensional changes due to moisture changes. Above-grade installations experience deflection, be they wood or concrete. If it is your turn to have Christmas for the family (yes, we get those calls), it will experience increased deflection it is not accustomed to.

All structures move, all tile moves. If you chose to roll the dice because you feel yours is different, that is your decision. Based on personal experience, having done thousands of installations over three decades, I would say 80% of the time you will be OK for 10, 20, maybe 30 years or more. The installation will likely fail due to lack of movement accommodation at some point. The question is – will you be there when it happens? Tough call to make when your desired ambiance will be destroyed by their inclusion. The cost to replace the floor will be double what it was going in. The risk management decision is yours.

Yes, I have had this conversation many times. By the way, stair-step joints are better than no joints and include a 1/4” at the perimeter if you do put them in. Keep both free of thinset. Believe me, it makes a difference.

ATE_1214David M. Gobis CTC CSI, Ceramic Tile Consultant

Ask the Experts – November 2014

SponsoredbyLaticreteQUESTION

I signed a contract with a company to renovate my guest bathroom: demolition, drywall installation, tile work and fixtures. The contract listed the color of tile to be used and color of grout. After the shower area was completed, I noticed the tiles were not all the same white. I checked the boxes and confirmed they did use three different colors. The company did not inform me they were using a mixture of colors. When I brought it to their attention that the grout in the shower area was wrong, they offered to reduce my cost by $88 or paint the grout. This company came highly recommended so I am very disappointed. Legally, should they rip everything out or should they compensate me a minimum of $3,000 if I have to live with this?

ANSWER

If you have a signed contract with a tile company designating a particular tile style and color and a particular grout color for an area, they are obligated to install those items according to industry standards. If they do not perform the work according to the contract, you should withhold payment until work meets the contract. If they mistakenly installed the wrong tile and grout color, you should expect them to re-do the installation so it satisfies the contract. If they wish to offer compensation for you to accept the work as completed, that is their right, but you are not required to accept this solution. You should receive the shower you contracted for. If you can live with the work provided and compensation will help you feel satisfied, that is probably the quickest solution.

I hope you have kept the boxes showing they used different colored tiles so you have some power in this situation.

Michael Whistler, NTCA presenter

1114_ATEQUESTION

I hear numbers thrown around about “how much rainfall equivalent your master shower gets” and I hear anything from like “a rainforest” to “1,000-2,000 inches per year,” but, do you – or does our industry – have any calculation of what the “annual rainfall” equivalent in a master shower would be?

ANSWER

I have the results of a study of a typical residential shower from Don Halvorson, Forensic Tile Consultant, (www.forensictileconsultants.com) that will probably surprise you:

Flow rate: 2.5 gallons per minute

Usage: 12-minute shower once per day

One gallon = 231 cubic inches

One day volume: 30 gallons=6,930 cubic inches x 365 days=10,950 gallons=2,529,450 cubic inches!!!!

And this is assuming a relatively low flow rate and only one shower taken per day!! More than 2.5 MILLION cubic inches!!!! If we could somehow get this staggering number conveyed to the general public (and state licensing agencies) I think tile installers would need to be licensed in all 50 states, because – like improperly installed plumbing or electrical wiring – an improperly constructed shower can damage your structure and cause potential health and safety hazards.

Michael K. Whistler, NTCA

Q: That is an amazing statistic or piece of information. I’m floored (no pun intended) to see the total amount of water flowing through a shower. YES, we should have a requirement that installers be licensed. In Texas, if you have a pulse and a trowel and someone foolish enough to hire you to build their shower…you’re in business! Thanks again and we’ll continue to push for good installation techniques and proper installation – it’s a must!

Ask the Experts – October 2014

SponsoredbyLaticreteThis month’s Ask the Experts concerns shade variation, and an ongoing conversation between the homeowner and David M. Gobis, CTC, CSI, Ceramic Tile Consultant, who works on an independent basis and on behalf of the Tile Council of North America. What this exchange makes abundantly clear is to be sure the homeowner or client – and the general contractor (GC) – understand the concept of shade variation before a single tile is installed. Perhaps a good rule of thumb is to dry-lay a section of the floor showing the variation and get the homeowner or GC to sign off on approval of it before actually installing the job. Otherwise, a surprised client may try to pin “responsibility” for installing “different color” tiles on you, the tile contractor.

QUESTION

I have had some porcelain tile installed in my home by an installer. The tiles were laid and he did not notice that one of the three tiles was a different color – laid it all anyway. Is there any place I can get a statement that the installer’s responsibility is to check the material before installing it? Any organization that specifies that the installer’s job is to do that before the tile gets stuck down? Many thanks.

ANSWER

There is usually a printed caution on the side of the carton to check the color before you install. It is a well-known issue. All tile varies to some degree, they have a rating system to try and make purchasers aware of the degree of variation.

David M. Gobis CTC CSI
Ceramic Tile Consultant

Q: I guess what I need is a source that states unequivocally that the installer’s responsibility is to inspect materials and check for color/consistency prior to application. Is there any standard or best practice guideline or requirement of a certified installer to do that check?

A: You’re not going to find what you’re looking for, but if he is CTEF certified you could ask him. I am not sure what they say in regard to that.

Q: I’m a homeowner with a new house, installer hired by GC and substandard tile stuck to the slab. I’m told the responsible party is the installer. I just need something that I can show to the arbitration judge – and I’m sure I’m not the first person in this predicament.

A: No, it’s a source of complaint all 42 years I have been in the business. Before we blame the installer what was the shade rating represented as being? Second, was all tile from the same lot number? Who bought the tile? Might seem like a lot of info to ask but when things go wrong you have to line up your ducks. You’re in a tough spot to win and you won’t without background.

Ask the Experts – September 2014

SponsoredbyLaticreteQUESTION

In March 2014, we moved into a new construction home in South Florida. After living here three months, we are noticing a large portion of our tile floor to be hollow sounding. The builder says it is normal because of the membrane/ wicking paper that is used. Is this in fact correct or do we have an installation problem? The contractor said the wicking paper was laid down to absorb moisture. We are also having problems with our grout crumbling, which we were told that that was lost likely from dirt getting in grout before it dried.

ATE_0914ANSWER

I have been in tile for more than 40 years and I have never heard of “wicking paper” or the need to absorb moisture under tile. The grout joints breathe and that is a good thing; that will take care of the moisture. Given your geographical location and nature of your problem, it sounds like the floor was installed over roofing felt or some other building paper. This is not an acceptable installation practice. That the grout is crumbling indicates it was likely over-watered in the mixing and/or cleaning process, which causes a weak, powdery condition. If you have floor tile movement, indicated by hollow sounds, the grout would then crumble in the joint. It would be a good idea to have a reliable consultant take a look at it. You might want to give the Florida Construction Law a quick read too.

David M. Gobis, CTC, CSI
Ceramic Tile Consultant

Editor’s note: On page 191 of the current 2013/2014 NTCA Reference Manual, Chapter 7, there is a statement titled, “Use of Felt and Similar Products as Crack Isolation Membrane.” It states that “Use of roofing felt, sheet vinyl, scribing paper, or scrim-reinforced kraft paper glued or unglued to both concrete slabs and over wood construction have a long history of failure,” even though they may be promoted as crack-isolation membranes. These faulty alternatives to tested products that meet ANSI A118.2 Crack Isolation Membranes for Thin-Set Ceramic Tile and Dimension Stone products “lack the performance features and criteria that would allow effective control of fractures without transmission through the finished tile surface.” Choosing these inferior products typically results in massive failures, tear-outs and replacement cost well after the warranty period has expired.

Ask the Experts – August 2014

SponsoredbyLaticreteQUESTION

I have an Absolute Black Granite triangle shape 20” x 20” – 1-1/4” thick that I would like to mount as a corner seat in my shower. Can this seat be mounted in the wall to handle the weight of a 230- lb. person ? No support under the seat. If that is possible, what is the best way to mount the seat in the wall?

mosaic_asktheexpertsANSWER

Our tile installation company installed hundreds of these. Of course, we were also a fabrication company, and we usually installed slab seats that matched the slab vanity/tub deck in the bath that we also provided.

The installation of these seats was very simple, but there was a trick – we would just cut the tile on both walls to accommodate the thickness of the stone and the length of each leg, but in order to get the end cuts tight enough to look good, the triangle of stone had to be installed at the same time as the tile on the walls (we would also be sure there was good mortar contact between the stone and the wall substrate). This required good, solid spacers in the installation for the joints under the seat.  The soft rubber ones didn’t work well. Once the mortar was cured, we would grout the wall tile, but use sealant (a.k.a. caulking) where the stone met the tile, the same as the inside corners in the shower.

Michael K. Whistler, Presenter/Technical Consultant, NTCA

QUESTION

We understand that curing compounds on a concrete substrate can impact the bond or adhesion of the mortar and cause installation failure. We are familiar with the recommendation to scarify or shot blast the floor to remove these inhibiting substances as well. But we would like to know if there is a manufacturer that offers or recommends a specific curing compound or primer/bonding agent to be used with a specific thinset, with proven results? We have a large customer we do work for and this issue continues to occur so we are looking for information we can provide for them.

ANSWER

Many manufacturers are coming out with primers that are mainly designed for tile-over-tile installations, but can also be used for many other problematic substrates. We keep hoping that a primer will be introduced that will have the capability of being applied to a concrete substrate with curing compounds that would not have to be removed. Unfortunately, we continue to be told by the manufacturers that these primers should not be used for this purpose. At this point in time we know of no primer, mortar or adhesive that is approved for use over a curing compound. What is really needed is for specifiers to understand this situation, so they can clearly point out in the design phase that areas that are to receive ceramic tile should be treated differently by the concrete contractor. Concrete substrates where tile is specified should receive a broom finish and have no curing compounds used that in area. That would make a significant difference and save everyone time and money.

Michael K. Whistler, Presenter/Technical Consultant, NTCA

Ask the Experts – July 2014

SponsoredbyLaticreteQUESTION

I’m interested in using mosaic tile on an upcoming project. Do you have any recommendations to ensure a successful job?

ANSWER

There are quite a few very important criteria to ensure long-term success for this project.

Use a mosaic that is rated for exterior use. Porcelain is excellent because it is considered impervious. But almost more important is the mounting method for the mosaic sheets. No paper-mesh, back-mounting should be used. Your course of least risk would be to specify a mosaic that could be used in a submerged application as well as for exteriors.

Work with a mortar manufacturer to come up with the best system to suit your project needs, including possible waterproofing and a mortar suited to your climate’s exterior rigors.

Application of mortar and mosaic sheets must be well done. Mortar should be flat-troweled into substrate, additional mortar applied and notch-troweled in one direction, then notches flattened with flat side of trowel. Apply mosaic sheets to fresh mortar and beat in with beating block. This method gives best coverage, minimizes mortar squeeze-up between tiles and gives a flat, uniform installation.

Expansion joints are vital and must be specified into the project according to EJ-171 in the TCNA Handbook.

– Michael Whistler, NTCA technical consultant

QUESTION

Recently an installer removed tile and installed new tile over the existing mortar/thinset. He said it’s a normal practice, and any tiles that are uneven (in terms of height), are within the industry standard of 1/16”. Does that make sense to you?

ANSWER

I think he is only telling part of the story. There’s no problem installing over old mortar, tile, or thinset as long as it is well-bonded and crack free. That does not change the tolerance which is 1/4” in 10’ with no greater than a 1/16” variation in 12” for tile under 18” and an 1/8” in 10’ with no more than 1/16” in 24”. The 1/16” he is referring to is a lippage allowance. Lippage allowance for installation is the height minus (or plus) the actual warpage. That allowance is 1/16” for grout joints 1/4” or greater and 1/32” for less than 1/4”.

David M. Gobis CTC CSI, fee-based consultant responding on behalf of TCNA.

QUESTION

Natural stone was installed as part of a renovation at our home. However, now there are muddy spots that appear to be staining the stone. Can you determine what would be discoloring our beautiful new stone and how it can be fixed or eliminated?

ANSWER

Without making a site visit and undergoing extensive testing (some of which would be destructive to the areas that are stained), I will not be able to give you a definitive answer to what is causing these “muddy spots.”

All natural stone has some risk of minerals leaching and or metal oxidation. Metal oxidation occurs most often with softer stones such as travertine. It is caused by iron oxide that is found naturally in these softer stones and reacts to the oxygen in the air or from exposure to water (which also contains oxygen). When the oxidation occurs, usually a reddish / brown color is produced – sometimes orange colors may appear when there are free minerals mixed with the oxide metals and water is introduced. These colors are looked upon as desirable by many that choose natural stone but sometimes they are not wanted. In those cases, a manmade porcelain tile may be a better choice, especially when installed in a wet area.

For more information, check with the consultants listed on our website, since these professional do make site visits and can determine causes and possible prevention measures. Visit https://tile-assn.com/Member/RecognizedConsultants.aspx?mid=125 to view a list of consultants.

Gerald Sloan, NTCA technical consultant

Ask the Experts – June 2014

SponsoredbyLaticreteQUESTION

What is the normal direction to lay herringbone tile (which way do the “arrows” point) in a secondary room with only one entrance? I would think they point in the direction from the door to the back of the room but I have seen them “sideways” which seems strange. The rest of the floors are strip hardwood laid in a normal front-of-house-to-back-of-house pattern. The room to get herringbone tile is a small, step-down wine room off to the side of the dining room.

herringbone_patternANSWER

It is common to use a herringbone pattern “square-to-the-room,” or in other words in a “front-to-back” layout, but a diagonal herringbone is also popular. It really depends on the end user or design professional to determine the directional layout of the tile pattern.

The tile contractor will often create a dry layout of tile in a small area and have it approved by the responsible party before beginning permanent installation.

The only reference to layout in the American National Standards Institute (ANSI) A-108 is Center and Balance: no cut tiles smaller than half-tile where possible.

This is a matter of preference. No written documents are available pertaining to what direction to install herringbone patterns.

Gerald Sloan, technical consultant
NTCA presenter

QUESTION

I would appreciate your assistance in letting me know if there are conditions under which it would be proper to use spot bonding for a 6” x 24” porcelain tile to be installed on a concrete floor? That is, if proper adherents and materials are used and coverage space is adequate (80% for residential tile) is it appropriate to use spot bonding?

I ask because the little information I could find online indicates spot bonding is never appropriate for floors under any circumstances.

ANSWER

You are correct in your search for suitability of spot-bonding installation methods. It is never acceptable to use spot-bonding for floors. Spot bonding is exactly what it implies, placing spots or dabs of mortar on the back of the tile or substrate, then pushing the tile down hoping the spots will expand enough to get proper coverage. This “spot expansion” really never occurs, giving sub-standard coverage. It is difficult enough to get proper coverage using a notch trowel correctly.

There is usually a reason installers want to use spot bonding, and it is that the substrate is out of plane and they need to build the tile up to avoid lippage issues. This actually causes two bad results: one – poor coverage; two – mortar applied too thickly, exceeding manufacturer’s maximum allowable thickness that leads to shrinkage and possible de-bonding. Substrates need to be prepared to proper flatness before proceeding with tile installation. Having a flat substrate allows faster installation and a better end product.

There IS one allowable method for spot bonding, and it is for walls only. There are manufacturer’s proprietary epoxies available that allow you to spot-bond tile to walls by using their products and following their written installation instructions.

– Michael Whistler, technical consultant
NTCA presenter