The Basics of Cracked Tile Prevention
October 17, 2011
Cracked tile remains a concern often expressed by customers considering ceramic tile floors. Many have had or heard of experiences where a few tiles cracked some years after installation and no replacement material could be found, necessitating a complete and costly replacement. The concept of crack suppression goes back to the mid ‘80s and was initiated by several manufactures of sheet products. Tile manufactured at that time was not as durable as the popular porcelains of today are, and cracking of tile was quite common. Having heard the concerns of consumers and necessity being the mother of invention, a new segment of the tile industry was born. Our choices are no longer limited to a few products. There are a plethora of crack isolation aids available today. Increased competition has lead to most individual manufacturers marketing a variety of products with varying performance attributes. This article takes a look at some of the basics of trying to prevent cracks in tile installation and what you should expect.
It is nearly impossible, even when trying to keep things simple, to not bring up product and installation standards. If I were a salesperson rather than an installer and technical consultant, I wouldn’t bother because it only makes life more difficult. But, fortunately for me, I have never been a sales person and never will be. So before we go into where and when a membrane is appropriate, what should you and your customer expect? There are few if any guarantees by a manufacturer that a membrane will stop tile cracks from occurring. This is spelled out in the American National Standard Specification for Crack Isolation Membranes for Thin-set Ceramic Tile and Dimension Stone Installation ANSI A118.12- 05 which says the following; “It should be noted that while crack isolation membranes are intended to minimize the potential for crack propagation from the substrate through the finished tile or stone installation, they may not always be 100% effective in preventing all defects in the finished tile.” Most manufacturer warranties are for membrane product replacement. Thus if you follow all industry and manufacturer installation recommendations, in most instances the best you can expect is some replacement material. There are very few exceptions to this statement and those that make that exception have numerous caveats attached to any type of material and labor warranty.
One of the more popular uses of a crack isolation membrane is the relocation of concrete control joints to the next nearest grout joint to avoid cutting the tile or disturbing the tile pattern. Things get a little complicated in this area. Many products do not allow for the relocation of control joints, especially liquids, though they are commonly used for that purpose. Those products that do allow for this practice have exacting instructions to make them effective. This is a particularly important consideration as there are several places where tile industry documents clearly say control joints need to be carried through the installation. Under the ANSI A 118.12 is says “It is particularly important when dealing with a cracked substrate that expansion joints are properly located and filled with a suitable sealant, or prefabricated expansion joint. Movement joints in the substrate shall be carried through the tile installation.” A control joint in the slab is defined as a movement joint by both the tile and concrete industry. Also new in the 2011 edition of the TCA handbook under EJ 171 Movement Joint Guidelines for Ceramic, Glass, and Stone you will find the following “All expansion, control, construction, cold, saw-cut, isolation, contraction, and seismic joints in the structure should continue through the tilework, including such joints at vertical surfaces. If proprietary crack isolation membrane is specified over saw cut joints to relocate a movement joint, contrary to EJ-171, the tile contractor is not responsible for cracking in grout joints or tile where tile has been installed over any such relocated movement joints, provided the tile, membrane, and other materials are installed correctly; this includes curling and/or deformation of the concrete occurring after installation of the membrane. Where a tile pattern falls diagonally across a saw-cut joint, relocation of the movement joint is specifically not recommended because of the reduced performance of the sealant when used in a saw tooth or other non-linear fashion.”
With that statement and others made elsewhere, any warranty expressed relative to the relocation of control joints is borne by the manufacturer entirely. You can be quite sure if a problem does occur and a claim is filed, they will be going through the installation products and processes with a fine tooth comb. Think you know enough already and aren’t worried about it? In preparation for this article I read through a series of manufacturer instructions to see what if anything had recently been modified. One recently changed set of instructions by a well-known manufacturer recommends using only a ANSI A118.11 EGP mortar and requires a 48 hour wait prior to grouting for all their products. I can assure you, you don’t know what you think you know, especially if you have not looked at a data sheet recently. Read the instructions!
So what will a crack isolation membrane do for you? When slabs crack there is usually a reason. All concrete slabs require control joints. Concrete is concrete whether a warehouse floor or a residential dwelling. All concrete shrinks as it cures. Control joints control where the cracking will occur. Something I have heard on numerous occasions throughout my career is that once the shrinkage has taken place the joint will not move. That is not a true statement. Concrete, like all building materials, will move with changes in moisture and temperature. The most dramatic display is perhaps the buckling of a road we hear about every so often; even sidewalks in Wisconsin buckle if anticipated movement is not properly accommodated. If you’re on a residential slab with no movement joints it begs for the use of a membrane because it is going to crack somewhere, sometime. If the slab is already cracked and there is no vertical displacement (one side is not higher than the other), a membrane will aid in keeping the tile from cracking. If you are tiling direct to a suspended slab, also known as slab on deck, that installation is also an excellent candidate for a membrane. All above-grade slabs move by design. Tile being a brittle clay-based surfacing material, it is not very forgiving of movement. All above-grade installations require some type of deformable installation system to allow for a reasonable amount of distortion in the tile installation system. In my personal experience I am seeing a lot of problems with big tile and small joints in above-grade applications due to lack of deformation abilities.
Somewhere along the way the thought process has developed that because you use a membrane movement accommodation joints are not required. Nothing could be further from the truth. If an installation is to have the ability to deform that stress must be transferred to someplace. You wouldn’t buy shock absorbers and have them welded together would you? What’s the point of using them at all if they are not going to absorb and transfer energy? That’s what crack isolation membranes do is store energy and transfer it to a different place rather than through the tile surface. That place would be the properly prepared movement accommodation joint. The bigger the tile and/or the smaller the grout joints the greater their importance. Space is getting kind of tight for this issue so we leave you with these additional cautions:
• When using liquids make sure to check your application thickness with a film thickness gauge. Most require around a 30 mil (.030 or 1/32”) thickness or greater. Any less and it is just colored concrete and incapable of absorbing and transferring movement.
• Make sure your selected product is rated for the intended application. Manufacturers make numerous products for varied applications. All are not created equal.
• Most membrane adhesives are moisture sensitive and should not be used over a slab with high relative humidity or moisture vapor emission. These limits can vary widely even within a manufacturers own product line.
• Anytime one side of a crack is higher than another a membrane is not going to help.
• In general, most membranes require a three-tile width of product to be effective in crack suppression or when approved for that purpose, joint relocation. Some require that only one tile be fully supported by the membrane. I am aware of only one exception to this generalization, with which I disagree based on my experiences with that very product.
• Membranes have no structural value. Adequate support must be provided by the structure. By virtue of their deformable nature they will accommodate a limited amount of structural deficiency, but you are treading on very thin ice if you chose to use them for that purpose.
• Never allow construction traffic over a membrane, they are hard enough to bond to without being soiled. This can and will affect the longevity of the installation.
I’m pretty sure I could write a small book about tile, stone, and membranes. The amount of products out there is almost overwhelming as are their varying requirements and performance attributes. Personally I have used three basic types of products consistently over the years. I have never found one that would work universally in every application. Studying the products and getting the best value and performance for a given situation can certainly be a challenge. I hope you take the time to read thoroughly so you can chose wisely. Change is never-ending.