Muhammad Ali Center Case Study
The Muhammad Ali Center is a historical and cultural landmark in Louisville, Kentucky. The board of the center decided to renovate the lobby to update and modernize the space, while also reflecting Muhammad Ali’s cultural significance. Part of this modernization included a demo of the existing floor, re-leveling, and installing a four-color terrazzo topping.
This project presented various challenges throughout installation, including a radiant tube heating system that reached excessive temperatures, moisture leaking from the curtain wall, and a post-tension slab with no control joints. The radiant tube heating system reached temperatures of 117° Fahrenheit and did not progress to these temperatures gradually, but reached them almost immediately. Terrazzo cannot withstand temperatures above 90° Fahrenheit, and is liable to crack due to thermal expansion if exposed to excessive temperatures.
The leak near the curtain wall posed the possibility of delamination of the terrazzo topping if not mitigated. Several areas were visibly damp due to moisture seeping in through the curtain wall, and this area tested at 100% relative humidity. Eliminating the source of the moisture was imperative before the terrazzo could be poured.
The substrate consisted of a post-tension slab that did not require control joints. This slab was over an unheated garage and the lobby had a two-story curtain wall that created significant thermal expansion and contraction due to sunlight and radiant heat. This thermal expansion and contraction could potentially crack the terrazzo topping.
Terrazzo Trade Standards
Radiant heating systems must gradually increase in temperature and cannot exceed 90° Fahrenheit when installed beneath a terrazzo topping. The recommended temperature range for terrazzo is between 60° and 90° Fahrenheit. The coefficient of expansion for epoxy is greater than that of concrete, so large temperature shifts could cause delamination and cracking. This particular heating system specified at least ¾” space between the radiant tube heating and terrazzo topping to help prevent damage from thermal expansion. The original slab encasing the radiant tube heating system was demolished and replaced with Tech-level 150. A terrazzo topping requires the substrate to have a tensile strength of at least 300 psi in order to prevent the epoxy from “pulling” the substrate, and Tech-level 150 provides a tensile strength of 333 psi.
The relative humidity must be between 75 and 80% before terrazzo can be poured. Any sources of moisture must be mitigated, or the terrazzo could delaminate. Proper moisture testing requires the ASTM-F-2170 deep probe test between the radiant heating tubes at two inches in depth.
Some post-tension slabs are engineered so that they do not require control joints. This particular slab did not call for control joints, so expansion joints in the terrazzo were necessary to prevent the terrazzo topping from cracking due to thermal expansion. According to NTMA standards, expansion joints are required in areas of potential stress or where radiant heat could cause thermal expansion, such as between columns and curtainwall.
Engineers were tasked with modifying the radiant tube heating system to gradually increase in temperature and to not exceed 90° Fahrenheit. The radiant heating system was turned off entirely during the terrazzo installation and remained off until modifications were complete. The original slab encasing the radiant heating tubes was demolished, and Tech-level 150 was poured to provide a barrier between the radiant heating tubes and terrazzo. 3/8” divider strip was used to prevent any contact of the metal with the tubing.
To prevent further moisture migration, the owner of the center hired a contractor to remove two feet of the sand-set paving on the exterior and to water-proof and flash the curtain wall. These measures sufficiently mitigated the moisture leak from the curtain wall, and the relative humidity tested at acceptable levels. Key Resin’s moisture vapor barrier was applied to the affected area.
Because the post-tension slab did not require control joints, expansion joints were added at various points of potential stress, such as around the curtain wall and between columns. Divider strips were also placed every twelve feet to aid in potential thermal expansion from radiant heat exposure from the curtain wall. These joints allow for the terrazzo to expand and contract with any thermal changes.
This job displayed several issues throughout the terrazzo installation, including moisture mitigation, thermal expansion due to sunlight and radiant tube heating, and proper placement of expansion joints on a post-tension slab. These issues were all addressed and abetted according to NTMA installation standards.
 Email from architect after reviewing radiant heat system specifications
 NTMA Email 7/24/14
 Statement from John Zilly, Technical Services at Custom Building Products