2024-25_NTCA_Reference_Manual_dig_dwnld

Crack-Isolation Systems

INTRODUCTION Crack-isolation systems for ceramic tile and stone installations are intended to accommodate anticipated movement and related stress that a substrate exerts on the installation without adversely affecting the performance or appearance of the finished installation. These materials are typically applied to existing substrates that exhibit shrinkage cracks, settling cracks, cracks associated with structural deficiencies or cracks related to the thermal movement of the substrate material. Yet, their application to new substrates that do not exhibit any of these deficiencies is steadily increasing. In these instances, crack-isolation systems are intended to negate or reduce the effects of cracks in the tile that might develop at a later date.

All concerned parties should be aware that the best systems may not overcome all deficiencies of the substrate. But, a crack isolation system is preferable to bonding the tile directly to the cracked substrate. The deficiencies noted in the inspection may become worse after installing the tile without a crack-isolation system. Remember, the crack-isolation system is intended to negate the noted deficiencies of the substrate. LIMITATIONS Crack-isolation membranes shall not be used to relocate any type of movement joints. Movement joints in tile shall coincide with movement joints in the substrate, i.e. construction joints (cold joints), contraction joints (saw-cut joints), expansion joints and isolation joints.

Even with a crack-isolation system, TCNA Handbook method EJ171 still requires expansion, control, and isolation joints.

Crack-isolation systems include, but are not limited to, composite sheet materials and cold, liquid-applied materials.

Crack-isolation systems are designed to work with cracks between level planes of substrates. When cracks in the substrate are not on the same plane, crack-isolation systems are of questionable value. In this case, expansion joints are required.

In some cases, crack-isolation systems can be applied in narrow bands over existing cracks in the substrate. In other cases, crack-isolation systems are intended for application over the entire substrate surface.

Isolation systems used on cracks brought to plane may offer some advantages, however, their value remains questionable.

Refer to TCNA Handbook methods F-125 Partial and F-125 Full for more information on the respective treatment methods.

Cracks over 1/8 in. (3 mm) in width are considered major cracks and may or may not be accommodated by crack-isolation systems. Attempt to determine the cause of the cracks and consult with available manufacturers to determine suitable application procedures. Some crack-isolation systems may not be capable of withstanding the rigors of certain installations. Consult with owners and manufacturers to determine the intended service requirements of the installation. The service ratings delineated by the Robinson Floor Tester, ASTM C627, may be useful for this purpose. CONCLUSION Effective use of crack-isolation systems involves pre-installation conference and consultation with all concerned parties. These discussions should include substrate evaluation, system application techniques and the limitations of the chosen crack isolation system. Finally, a qualification regarding the acceptability of any cracked tile or grout joints should be determined and agreed upon by all concerned parties before any work begins.

For proper performance, individual manufacturers must be consulted for specific installation instructions, application techniques and any system limitations. Follow the individual manufacturer’s written instructions precisely.

Contractors are not encouraged to design their own crack isolation systems since the inherent liability of a failure is so great.

PRELIMINARY Inspect and identify the nature and extent of the problem.

Qualify the situation to determine the expected results, i.e. the acceptable level of cracked tile or grout joints after the procedure has been accomplished. Contact the manufacturers of crack-isolation systems to determine if their materials can accommodate the existing conditions. Request that they visit and inspect the installation.

110

NTCA Reference Manual | 2024 / 2025

Chapter 4 | Membranes