Crack-Isolation Systems

  They lead to unhappy customers, callbacks and significant challenges when matching replacement tile and grout. Cracks can have an adverse effect on contractors’ pocketbooks, but more importantly, their reputations.
  That’s the bad news.
  The good news is the risk of cracks can be reduced through the use of crack-isolation systems. It just takes some know-how and advance planning.
 
WHY CRACKS?
  The unfortunate reality is that cracks are an unavoidable byproduct of concrete. As the water used in the original mixture evaporates, the concrete shrinks. While this shrinkage may go on for several years, about half of concrete shrinkage occurs within the first 60 days after pouring. In most cases, shrinkage cracks won’t develop in concrete more than three years old.
  Although contraction or control joints may be incorporated into the concrete to regulate the location of cracking, they’re not always effective. Cracks can still develop randomly.
  Typically, stone tile is rigidly bonded to the concrete. As the cracks open, stress is transmitted from the concrete to the tile causing the tile to crack as well. That’s when the trouble begins.
  The potential for cracks in stone flooring is a growing concern for a variety of reasons:
  • First, the use of concrete slabs as a flooring substrate in residential applications is common in some areas, most notably the Southern and Western United States.
  • Second, thinner sections of marble tile are becoming popular in flooring applications. This thin tile can be vulnerable to shrinkage-crack transfer.
  • Third, the desire for speed and efficiency by builders leads to a push for tile installation on so-called green concrete slabs that are only a few days old. Traditionally, there was a 28-day wait for concrete to cure before tile was installed.
 
THE SOLUTION: ISOLATION
  The solution is to isolate the concrete from the stone tile, thereby preventing the transfer of the crack. Although there is more than one way to accomplish this, the crack-isolation system is a preventive measure incorporated in the tile- or stone-setting process.
  It’s important to note that crack-isolation systems can only prevent cracking that results from horizontal movement of the concrete substrate. In addition, crack-isolation products are not meant for structural cracks, or cracks resulting from loads on the tile or caused by building settlement/movement.
  A crack-isolation system also can’t compensate for deficient structures or flawed designs.
 
WHAT IS A CRACK-ISOLATION SYSTEM?
  Crack-isolation systems are available in several formats. They include:
  Mortars: Typically cement-based with a polymer additive, these flexible mortars are designed to isolate cracks and set the tile in a single step.
  Membranes: These consist of sheeting, liquids and trowel applications. The sheeting material (such as polyvinyl, polyethylene or butyl) is placed atop a layer of mortar or adhered directly to the substrate. Another layer of mortar is needed to set the tile.
  A basic crack-isolation method, utilizing a cleavage membrane, involves placement of a paper or plastic sheeting over the substrate and then applying a thick (1 1/2 inch) layer of mortar. All of these sheeting membrane systems typically require two or three installation steps.
  Liquid membranes may be acrylic or contain asphalt-modified materials. These membranes, some of which may incorporate a fiber mat, are applied to the substrate, allowed to dry, and topped with mortar to set the tile for a two-step process.
  Trowel-applied membranes are also applied to the substrate, allowed to dry, and then topped with mortar to set the tile as another two-step process.
  Recent advances in chemical engineering simplified crack-isolation -system installation. That’s important in an industry where time is money.
  For example, a one-step mortar is a dry powder, including polymers in the same bag, which simply mixes with water. Some can isolate shrinkage cracks that move up to 1/8”. Because the crack-isolation and tile setting is accomplished in a single step, this type of mortar has a number of benefits, including the fact that it lets installers be more productive.
 
STANDARDS AND WARRANTIES
  Performance data and manufacturers’ warranties provide useful guidance in selecting a crack-isolation system.
  The American National Standards Institute (ANSI), which develops performance guidelines for many building products, is developing new standards for crack-isolation systems that are expected in the near future. Until those standards arrive, reviewing published performance data is an excellent tool for investigating crack-isolation systems.
  One piece of performance data — the performance rating for crack-isolation systems — will help match a system with its intended application. The American Society for Testing and Materials (ASTM) C627 Robinson Floor Test determines the appropriate traffic capacity for a given crack-isolation system. These performance ratings range from residential to extra heavy duty. For example, a typical commercial building installation requires a moderate-duty rating, while an automobile showroom or service area requires a heavy-duty rating.
  In reviewing manufacturers’ warranties, it’s important to remember the two types of warranties that are generally offered: defect and performance.
  The manufacturing defect warranty — the most-common — simply promises that the manufacturer will replace the defective product. A performance warranty promises to deliver a specific crack-isolation performance, such as protecting against cracks that are subjected to horizontal movement of up to 1/8” for specified period of time.
  Some manufacturers offer more aggressive warranties. These include 1/8” crack protection for up to 12 years if the installation uses the same manufacturer’s crack-isolation system and grout product. These single-source warranties provide the buyer with additional peace of mind.
 
WATERPROOF IF NECESSARY
  Stone flooring is sometimes used in wet areas, such as bathrooms. But because stone isn’t a natural moisture barrier, the substrate can be damaged by water. In addition, excessive moisture can lead to mold and mildew growth. The solution is to install a waterproofing membrane before setting the floor.
  There are a variety of waterproofing membrane solutions ranging from liquid to sheet membranes. Some liquid formulations require no mixing while others consist of two or more components that are mixed on the job. Depending on the liquid formulation thickness, the membranes can be applied with a roller, brush or trowel. In addition, some liquids require mesh to be applied to the substrate.
  The project deadline is nearly always a consideration when selecting a waterproofing membrane. Generally, additional steps —such as the installation of mesh or sheeting — require additional time. Fortunately, today’s technology allows some liquid-based waterproofing membrane products to be installed in one step. Also, these products can be installed over concrete that is just three days old and be ready to allow tile to be set within two to three hours after application.
  It’s also important to note that the crack isolation properties of waterproofing membranes can vary greatly. Some merely “guard against” cracks but don’t provide a guarantee. Check the fine print. What you will find is some fall short.
  Another consideration in choosing a waterproofing membrane is mold protection. Mold and mildew is unsightly and can contribute to health problems for people with allergies or sensitivity to fungi. In fact, ANSI standards require all waterproofing membranes to prevent mold growth.
  Some waterproofing membranes take the requirement a step farther and are tested against the most stringent test method available: “ASTM D5590 Standard Test Method for Determining the Resistance of Paint Films and Related Coatings for Fungal Defacement by Accelerated Four-Week Agar Plate Assay.” It’s worthwhile to investigate a waterproofing membrane’s effectiveness against mold.
 
REPAIRING INSTALLED STONE
  Sometimes shrinkage cracks show up in stone flooring after installation. These cracks can also be addressed with crack-isolation systems, particularly if the concrete is more than three years old.
  To repair the affected area, remove the tile at a minimum of 150 percent of tile width or approximately 12” on either side of the crack. The substrate crack should then be addressed with a liquid crack-isolation membrane. Applying a membrane with a required thickness of 50 mils or less will make it easier to set the replacement tile at the same plane.
  But, not all cracks are the same. Shrinkage cracks are typically 1/8” or smaller. Cracks caused by structural issues, such as movement of adjoining slabs, are larger than 1/8” and can’t be addressed with crack-isolation systems. The remedy for cracks of this nature depends on the possible cause, and requires consultation with a design professional.
 
DON’T IMPROVISE
  Avoid the temptation to improvise a crack-isolation system on your own. There’s a danger that loss of the membrane can result in the stone cracking.
  There are numerous good, easy-to-use crack isolation systems available on the market – with manufacturer’s warranties. But improvised systems have no guarantees or performance guidelines.
  Although there are many choices of crack-isolation systems, selection needn’t cause headaches. Study the latest technology, carefully review performance data and read the warranties to find a crack-isolation system that cost effectively addresses your needs.
  Sandra Eich manages the TEC brand of setting systems, which include surface preparation, mastics and mortars.
 

This article first appeared in the December 2004 print edition of Stone Business. ©2004 Western Business Media Inc.