Installing porcelain tile on a concrete slab deck

QUESTION

Can you give me some installation guidance on the following scenario? We are installing 1,100 sq. ft. of 4” x 8” porcelain tile on an 18-month-old slab concrete deck in Chicago. Do I need to install a membrane at all? Do the risers also need to have membranes?

ANSWER

Thank you for reaching out. Based on the information you’ve provided, there is not a blanket industry requirement that an exterior concrete slab receive a membrane simply because it is 18 months old. The decision to include a membrane should be based on the specific project conditions and the performance requirements of the assembly.

Since this project involves an exterior installation in Chicago, freeze/thaw conditions, moisture management, drainage, and movement accommodation are all critical considerations. Before proceeding, I would evaluate the slab for cracking, proper slope and drainage, existing control and construction joints, and any other conditions that could affect the long-term performance of the tile installation.

TCNA Handbook standards: The installation should comply with the movement accommodation joint requirements of TCNA EJ171 in the TCNA Handbook for Ceramic, Glass and Stone Tile Installation. Existing control joints, construction joints, cold joints, and expansion joints in the concrete must be honored through the tile assembly, and additional movement accommodation joints should be installed in accordance with EJ171, based on the size of the installation and the environmental exposure.

ANSI Manual: Another consideration is ANSI A108.20 Section 10.2, which recognizes that not all compressible membranes are appropriate where heavy rolling loads or concentrated point loads are anticipated. If a membrane is specified, the design professional or building owner should work with the tile, membrane, and setting material manufacturers to ensure the selected system is compatible with the intended service conditions and approved for exterior use.

Manufacturer’s instructions: If a membrane is incorporated into the assembly, I would also recommend following the membrane manufacturer’s installation instructions for all transitions (including the risers), providing specific detailing at changes in plane to maintain the intended performance of the system. Not all membranes are rated for exterior applications. If a crack isolation, waterproofing, or uncoupling membrane is being considered, it is important to obtain a complete system recommendation from the membrane and setting material manufacturers to ensure the products are approved for the specific exterior application, environmental exposure, and expected service loads.

Slope: Because this is an exterior installation, I would also verify that the concrete has a proper slope away from the structure and that water will not be trapped beneath or behind the tile assembly. A membrane can help manage certain conditions, but it can also create problems if water is allowed to collect with no proper drainage path.

Consult the tech team at the setting material manufacturer: My strongest recommendation would be to contact your setting material and membrane manufacturer before moving forward. Review the project conditions with their technical services team and work together to develop a complete installation system that is appropriate for this specific application. Doing so helps ensure that all components are compatible, that the system is approved for the anticipated service conditions and exterior exposure, and that both you and the manufacturer are confident in the installation you are standing behind. Taking the time to obtain those recommendations in writing can provide valuable peace of mind and help avoid potential performance issues down the road.

Ask the Experts Q&As are culled from member inquiries to NTCA’s Technical Team. To become a member and make use of personal, targeted answers from NTCA’s Technical Team to your installation questions, contact Jim Olson at [email protected].