And then Warner Bros announced not just one sequel, but two. Fans went absolutely bananas, and America experienced its first-ever transmedia entertainment event. Leading up to the release of The Matrix Reloaded, Warner Bros released The Animatrix and trailers for Enter The Matrix, a cross-platform video game whose story was tied into the story of Reloaded.
For years, people who wanted to see 007 in action had to put up with plots that hinged on ridiculous things like invisible cars, laser beam satellites, and Madonna still being considered a sex symbol. This installment expunged the implausibility that plagued previous Bond films, establishing Bond as a grounded, conflicted character who just so happens to be hired by the government to play a friendly game of cards with terrorist masterminds instead of, you know, killing them.
Centuries ago, European builders developed a reliable means of installing tile for high-traffic, high-use applications which relied on the laying of a sand strata between the structural substrate and the mortar-bed/tile composite top layer. Due to space (height) requirements and other concerns, the sand strata method for tile installation is, for all practical purposes, extinct. Modern theory, however, explains that the sand strata \"uncouples\" the tile from the structure, allowing structural movement without damage to the tile layer. Approximately fifteen years ago, a modern analog of the sand strata system was developed in which a thin, polyethylene sheet membrane with a grid structure of square, cutback cavities and an anchoring fleece laminated to its underside, functions as the uncoupling layer. This article will provide the basis for the claim that a configured membrane allows the normal loading forces exerted on the tile surface to be widely distributed through a forgiving shear plane, similar to that which would be expected in the sand strata. These results contradict other work and theories which suggest that extremely strong bonds are necessary between the tile and substrate to maintain a crack-free tile surface. In fact, it is proposed that a weak interface is more forgiving, allowing substantial movement in the substrate without any evidence of cracking in the tile or the grout joints. This system also allows differential expansion and contraction between the tile and the substrate and can be used on a wide range of substrates which have traditionally been viewed as problematic; including plywood, OSB, post-tension concrete slabs, green concrete, radiant heated floors, and gypsum underlayments. To understand how this system accommodates stress within a tile assembly, the stress-strain relationship for materials under load will be reviewed, followed by a ceramic matrix composite analogy that illustrates how stress buildup and stress reduction are possible within composite layers. The shortcomings of directly bonding tiles, or setting tiles in a force-conductive assembly, will be evaluated in the context of large-scale tests performed on tile directly bonded to concrete slabs. Finally, it will be demonstrated that an effective means of \"uncoupling\" the tile covering from the substrate, fundamental to successful tile installations, can be achieved in a contemporary thin-bed application.
Movement forces are present in all tile installations due to the dimensional instability of construction elements that make up the assembly. Dimensional instability is largely a function of changes in moisture content, temperature, and loading (both dead and live loads) of the construction elements themselves. The resultant forces can be classified as compressive, tensile, and shear and manifest at the shear plane or material interfaces of the tile sandwich. It should be noted that these forces occur in combination.
Centuries ago, European builders developed a reliable means of installing tile for high-traffic, high-use applications which relied on the laying of a sand strata between the structural base and the mortar bed/tile composite top layer (Figure 1). The sand strata was the intermediary component that uncoupled the tile from the structure, allowing structural movement without damage to the tile layer. In addition, it allowed the normal live load forces exerted on the tile surface to be widely distributed throughout a forgiving shear plane.
A more recent analog of the sand strata method is a wire-reinforced mortar bed over a slip-sheet or cleavage membrane. As shown in Figure 2, the principle elements that make this type of installation viable are: 1) the mass of the mortar bed holds the floor section to the structural base; 2) the mortar bed provides an effective load distribution plane, allowing normal live load forces exerted on the tile surface to be widely distributed throughout the assembly, and 3) the cleavage membrane isolates the entire floor section from the structural base, preventing stresses in the building structure from telegraphing through to the tile covering. However, the principle disadvantage of this system compared to the sand strata method of installation is that the mortar bed can contribute to the assembly its own dynamics (e.g. shrinkage during the hydration process, thermal expansion and contraction, curling, etc.), which can lead to damage of the tile covering.
Nonetheless, due to many factors (e.g. assembly height and weight, which, in most cases, affect the structural design requirements of today's building environment; economic viability; the shortage of skilled labor; and the demand for simplification of the installation process), the sand strata method for tile installation and its more recent analog are, for all practical purposes, extinct.
Today, the landscape has changed dramatically. The most fundamental change our industry has undergone in the last millennium has been the shift from the traditional mud-set installation to the thin-bed or direct-bond method of installation, as illustrated in Figure 3. The implications of this shift are profound and far-reaching.
The direct bond method of tile installation, in which the tile is directly bonded to the substrate using a thin bond coat. No method of uncoupling is used in this case and, as illustrated on the right, cracks in the substrate become cracks in the tile.
Traditional wisdom has always maintained that an intermediary component that allows for independent movement between the tile covering and the building structure, without contributing a dynamic of its own, is necessary to achieve a crack-free tile surface. In light of this, contemporary wisdom states that an extremely strong bond between the tile and substrate is all that is needed in a directly bonded system to achieve a crack-free tile installation. The problem with this line of reasoning is that the contribution of each layer in a traditional system to the system's overall mechanical viability is either ignored or not addressed.
The modern analog to the sand strata method. The image on the left illustrates the configured nature of the polyethylene sheet, with the polyethylene fleece bonded to the bottom. The right shows the membrane in a typical installation, serving to uncouple the tile layer from the substrate, allowing the tile assembly to act independently from the substrate.
To provide a basis for evaluating the various bonding systems, and the causes of installation failure, it is necessary to briefly review the importance of the stress-strain relationships for materials under load. Figure 5 is a typical stress-strain relationship for a ceramic (brittle) material. There are basically two ways of approaching the stress-strain problem: 1) from a perspective of the applied stress; and 2) from the viewpoint of the strain within the material.
The second approach views the problem as the amount of strain a material can sustain until failure occurs. In this case the amount of stress exhibited in a material is dictated by the amount of strain imposed. If the strain is sufficiently large, the critical stress is exceeded, resulting in failure. As before, the failure mechanisms are identical - the perspective is slightly different however. This perspective is ideal for interpreting tile installation failures (and successes).
In the case of tile installations, the strain level can be developed through a number of avenues, and as such, the strains are additive. As described above, these strains are proportional to stress levels, and when a critical amount of stress is developed, failure in the form of cracking or de-bonding takes place. There are several sources of strain in a tile installation, as discussed below.
These strain development routes can be naturally grouped into two broad categories: tension and compression. In ceramics in general, compressive stresses are desired, but in the case of tile installations, as noted previously, excessive compressive stresses will produce buckling. However, in a directly bonded system, tensile stresses must be avoided, as they will almost always lead to cracking, either in the grout joint, the mortar bond coat, or in the tile. Even if small tensile stresses are present, cracking can occur in the bond coat, providing a location for future cracking of the tile surface - again, either within the tile itself or in the grout joints. In addition, significant shear stresses can develop between the tile and the bond coat, and/or between the bond coat and the substrate, leading to tile de-bonding.
Allowance for stress development during the installation process has traditionally been compensated for by using the more recent analog of the sand strata method. There are two principle methods for executing this style of installation. One method is to install the tiles on a mortar screed that is still plastic. Immediately covering the freshly placed mortar with tile slows the rate of hydration in the mortar screed, thereby reducing the amount of stress exerted on the system due to shrinkage. The second method is to install the tiles using a dry-set mortar after the mortar screed has cured. Once the tiles are placed, the dry-set mortar is allowed to cure, thereby reducing the effects of shrinkage. If the tiles were installed before the mortar bed cured, additional residual stresses could develop in the tile layer, potentially leading to cracking. In addition, mortar mixes used in installations of this genre have traditionally been lean mixes to keep the internal stresses of the screed to a minimum. 153554b96e