It All Moves – Plan on It
 
November 2nd, 2008

November – December 2008

By David M. Gobis

This month we are going to talk about what causes the overwhelming amount of ceramic tile failures. In my opinion, it is lack of movement accommodation. This is not a belief I have always had nor would I have even been receptive to, until the past 10 years of answering email and phones.

Being industry based, we typically get a different type of caller than most do in sales and manufacturing. If someone calls an industry-based organization they are looking for information, not claim accommodation, which is a whole different call or email. We tend to get much more information and are more able to get a factual picture of the issue at hand. That is not to say we are able to get all the facts. My most commonly uttered or typed phrase is “based on the information provided.” Nonetheless, people can be quite candid when they want to learn, as opposed to making a call which affects their financial well being. This is the reason I have come to my opinion on movement accommodation.

But wait a minute—we are talking about ceramic tile, and most commonly porcelain tile (called porcelain stone tile by some)—solid as a rock! Rock solid or not, all tile moves! Not only does all tile move, but so does every other product known to man—even the strongest steel or concrete has a movement rate that must be accommodated in the design process.

START WITH THE TILE

So just what necessitates this overwhelming need for movement (expansion) joints? It starts with the tile itself. Many people are quite surprised to hear that ceramic tile, a product manufactured by firing clay and other minerals at several thousand degrees, expands when exposed to direct sunlight. Porcelain tile, a very dense-bodied product with a very low thermal expansion rate, expands approximately .000004 inches per degree Fahrenheit. Sounds minimal, but that same porcelain tile covering 40 linear feet exposed to a change in surface temperature of 50 degrees Fahrenheit has the potential to expand between 1/16″ and 3/32″.

The adhesion of the bonding material to the tile and substrate reduces the actual amount of expansion but does not eliminate it. This is where coverage and type of thinset can make a big difference in whether the tile stays in place or not.

Types of tile other than porcelain, especially glass, are much more expansive under heat. Thermal expansion is a two-way street. Tile both expands and contracts due to thermal variation. This is one reason for my personal preference for using the term “movement joints.”

MOISTURE IS EXPANSIVE

If I were only concerned about moisture, then I could use an expansion joint. Why? Moisture is an expansive force on ceramic tile. Once it expands, it does not contract. This growth rate is very slow and very minimal. Except for this minor amount of growth, ceramic tile is unaffected by moisture or water; it is an inert material.

When someone says they have a tile failure due to excessive moisture, what they should really be saying is “due to defective workmanship.” Either they used the wrong thinset—it did not allow full curing prior to

moisture exposure—or there are no expansion joints and likely a few other ills.

Failures due to moisture expansion can happen in as little as a few years in areas of very high water exposure applications, such as an exterior deck or restaurant kitchen with no movement joints. However, most often they take a number of years to occur. Coastal areas such as Florida and New Orleans which have very high ground water tables show a disproportionate amount of slab-on-grade moisture-related failures, most commonly due to a lack of movement accommodation joints.

Ironically, I just finished that paragraph and received an email about multiple failures in a slab-on-grade application that is between two and three years old. I would say the thoughts the flooring contactor expressed, while vastly inaccurate, are typical of what we receive. Here is the unedited text of his letter to the owner (with the name altered, of course):

“Wearethebest Floor Company does not consider the ceramic tile installations that are shearing off the floors in your home’s a result of improper installation or due to defective material. Therefore, these occurrences are not covered by Wearethebest Floor Company’s warranty. Upon review of inspection reports and photographs, it is our opinion that one or two circumstances or a combination of both caused these failures. Vapor transmission, also known as vapor pressure, occurs in all concrete surfaces in the form of a gas vapor. This process of moisture emission is natural, necessary, and driven by nature through capillaries within the concrete. Water vapor always migrates from a cool wet environment (concrete slab) to a warm dry environment (building interior) through a process known as diffusion. Moisture movement can occur from capillarity, absorption, and gaseous diffusion. Vapor pressure can be measured but not calculated (predicted). Concrete permeability and porosity govern vapor emissions. Since all the failures occurred after the Wearethebest Floor Company’s warranty period, something occurred to cause a drastic increase in vapor transmission (i.e. extreme rainfall that occurs with a hurricane), the increase in the vapor transmission would result in increased release of alkaline salts from the concrete. When the vapor comes in contact with the bond line, it then turns into liquid and the salts in the liquid infect the bond line and cause the tile to release The tiles inspected typically had thinset on the tile, but it had broken free at the concrete, which is what happens with this phenomenon. There are tests that can be done on the concrete, and I could provide you with the independent company that performs these tests. As a word of caution, these tests will not show how many PSI were in the concrete at the time the tiles sheared from the floor.”

In my opinion the evaluation is completely off base and the explanation without merit. To insert my response would take more space than allowed for this article. The only effect moisture had on this installation, even if the home was flooded, was moisture expansion of the tile and concrete, which happens in every slab on grade installation. Thinset does not liquefy; it is very alkaline and, like concrete, it is made out of cement. That it is stuck to the tile and not the slab does provide some insight.

While I have not seen this particular project, based on the information provided, I would speculate a lack of movement joints combined with tile thinset over curing compound. I did later receive confirmation that both were correct. This project, in a coastal area, is very typical of the calls and emails we receive. The company, a well-known and respected entity, says they never use movement joints on residential projects and this is just one of the normal installation issues in their area.

Now that is truly burying your head in the sand. If I sound irritated, I am. These good people who chose tile for their homes deserved properly trained installers and sales personnel. Instead, they now face substantial personal expense in either repairing the floor or for attorneys’ fees to sue for a latent defect in installation.

Lest we further digress, what are some other good reasons for movement/expansion joints?

WOOD MOVES

Wood structures are going to move. All wood supported floor systems have a certain amount of deflection. Too much movement can cause a host of problems, but even normal movement from bending stresses must be accommodated.

Perimeter joints are critical in wood structures to accommodate the normal movement of the structure and seasonal moisture changes in the wood itself. If there is a beam running down the center of the room or home, common sense tells us that is a pivot point from which the floor will deform on either side, like a board over a fulcrum. It would be prudent to put a soft joint or movement profile over that area to allow the floor to move without putting the tile assembly in stress.

Another area of consideration is doorways. Take the example of a kitchen with an adjoining dining room. If we have a 300-square-foot kitchen with a doorway to a 250-square-foot dining room, both installed over backer board, we have roughly 1800 pounds on one side of the wall and 1500 pounds on the other side, joined together at a 3-linear-foot doorway, like a barbell. Again, common sense would say this is not a good idea and real world experience confirms it isn’t—you need a movement joint.

Most areas of the country go through seasonal changes in humidity levels. These changes affect the dimensional stability of the supporting floor structure. This moisture-induced movement is magnified several times if the method of construction utilizes a crawl space, which subjects the supporting structure to a much greater level of dimensional instability.

CONCRETE SHRINKS

Concrete does not earn a free pass on stability either. Did you know that concrete spends its whole life moving? Concrete has a natural tendency to warp. Control joints are placed primarily for concrete shrinkage during the initial curing process. Because a concrete control joint is not cracked at the time of tile installation does not mean it will not crack at some point. In all likelihood, you can be fairly well assured it will. If there are no control joints in the slab this cracking will occur at random locations over a period of time, which can be many years.

Movement/expansion joints must be provided at all control joints. As the concrete continues to fully cure, which can take as long as a year, some additional shrinkage will occur, and control joints provide the means for dictating where the separation will happen. Even after the concrete is fully cured there will be some minor warpage. If tile is installed without the proper movement accommodation joints it is quite possible that it may either crack or debond.

Using a membrane does not eliminate the need for movement joints. For a membrane to function properly movement joints must still be placed in the installation, though some products and methods will allow you to select a more atheistically pleasing location.

The physics of concrete is very complicated but it is not as unpredictable as many think. The cause and effect is actually rather well defined. It is a fact, all building materials move, none at the same rate. All structures move by necessity. This movement coupled with the dimensional characteristic s of the flooring material must be accommodated in the design process.

INCLUSION A CHALLENGE

Architects, general contractors, owners and end users are very averse to seeing caulk and sealant joints or movement profiles that they feel destroy the ambiance of their home or structure. I am from the real world of installation and understand the challenge of their inclusion. It was a battle I fought on nearly every job of any substance.

Awareness of the need for movement joints in tile installations needs to begin at the sale or specification stage, well before ordering products and certainly before the installer arrives on site. Asking the purchaser or end user how they prefer these joints to be treated should be no different than, and is of much greater importance than, selecting grout color. Caulk, sealant, or profiles should be ordered at the time of sale to make sure they are on hand for the installation process.

Tile flooring is an investment, not a commodity, and measures should be taken to protect it as with any investment. Why not take a look at your current policies regarding expansion/ movement accommodation joints and see what you can do to better protect your company and those who invest in your products?

 

David M. Gobis, a third-generation tile setter, is the Technical Director for the Ceramic Tile Education Foundation. He has been in the trade for over 35 years and owned a successful contracting business for many years prior to his current position. Mr. Gobis is an author of numerous trade related articles and a frequent speaker at industry events. He is member of the Construction Specification Institute, International Code Council, American Concrete Institute, National Tile Contractors Technical Committee, voting member of The American National Standards for Ceramic Tile Installation and Setting Materials (ANSI A108/118), American Society for Testing of Materials (ASTM) C-21 Ceramic Whitewares, and Tile Council of America Installation Handbook committees. © 2008 Dave Gobis CTEF

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