Masonry Magazine October 1992 Page. 25
Is Thinner Better?
Thinner can be a disaster for tile and marble over the lightweight substrate using the resilient setting materials for heavy duty commercial flooring.
COMPUTERIZED design of commercial structures over the last decade has enabled architects and engineers to eliminate the traditional "built in" safety factors of added concrete and steel. It's now possible to construct lightweight structures at a more economical cost than the old masonry or reinforced steel and concrete buildings. The use of post tensioned concrete and prestressed concrete systems is becoming more and more common. These new lightweight systems allow floor bending and deflection that didn't occur in the older more rigid systems.
Other changes were taking place in the construction industry. Architects and engineers found that the tile (ceramic, marble, agglomerate and terrazzo) industry had developed materials that would bond hard surface flooring materials directly to concrete. No longer was it necessary to install tile, marble or terrazzo on a thick mortar bed. It was several years and many bonding failures later before it was discovered that thinbed bonding materials were coming loose and buckling up in the new lightweight buildings.
Epoxy reasonably successful
One of the first recommendations was to increase the bonding strength by using an epoxy bonding material. In general the epoxy was reasonably successful except for occasional transfer of the bonding failure to the separation of the concrete topping or the transfer of the concrete crack through to the surface of the tile or marble. Because the epoxy was expensive, mortar manufacturers conducted a good deal of research into less expensive alternatives. This resulted in several new bonding materials containing latex and acrylic additives which increased the resiliency and bonding strength, so that the new materials would be superior to the original Tile Council dry mortar formula.
Latexes provided a good bond
The new latexes provided a good bond (not as good as the epoxy) but the problem of concrete cold joints and cracks that are not in alignment with the tile or marble expansion joints was still causing a lot of tile cracking and tile buckling. Some mortar manufacturers increased the resiliency of their bonding material sufficiently to allow some substrate cracks to be covered without the loss of bond or the transfer of the concrete cracking through to the finished floor. The market had broadened and very large expanses of tile and marble were being set in the thinbed method. The American National Standards Institute and the Tile Council of America state that the only approved method to install tile on a concrete substrate is to place all substrate joints in direct alignment with expansion joints in the tile floor. Attempts by the architect to draw and specify the substrate cold joints, control joints, and expansion joints in order to meet the ANSI and TCA requirements are impractical if not impossible for the contractor to achieve in the field.
The amount of misalignment is not important. One quarter of an inch or four inches causes bond loss or cracked tile when the tile is set with the old or new latex mortars in most instances.
It's not possible to predetermine the amount of substrate movement in an existing concrete substrate. Apparently, slab on grade movement can vary considerably within fifty to one-hundred feet of each other. Slab above grade movement can also vary sufficiently to confuse the "experts" as to why one area lost bond and the other did not.
Crack isolation system created
The bonding material manufacturers continued to burn the midnight oil in their research and development laboratories. The "crack suppression" or "crack isolation" systems were created in an attempt to allow the tile joint and the substrate joint to be out of alignment without the usual bond loss or crack in the finished floor. The principle of the systems is to provide a resiliency that will allow lateral movement under the tile without causing surface cracking or loss of bond. Various manufacturers recommend placement of additional soft or expansion joints in the tile parallel to the substrate joint. The success of the system depended upon the unpredictable amount of substrate movement and the resiliency of the system. The more resilient the system, the more successful, as far as tile bond loss and crack transfer to surface was concerned.
A new era had been reached in bonding tile to bending, deflecting, and cracked slabs with misaligned control joints. By using a super elastic latex bonding mortar and installing a resilient crack isolation system the architect could design circular patterns in a rectangular module and the contractor could continue to saw concrete control joints that are bowed or out of square and impossible to follow with the straight joint in the tile. The elastic bonding material permitted the substrate to move independently from the finished surface.
If the story could end here, we could all live "happily ever after." Unfortunately it doesn't so as Paul Harvey would say, stay tuned for the "rest of the story."
Architects and engineers had cut building costs using lightweight design and materials. Mortar manufacturers designed flexible bonding materials and resilient crack isolation systems to compensate for the bending, deflecting, and cracked substrates.
While all of this was taking place, quarry tile was reduced from 34" to ½ thickness. Porcelain pavers are MASONRY-SEPTEMBER/OCTOBER, 1992 25