Crack Detailing & Joint Treatments for Epoxy Terrazzo

Thin-set epoxy was traditionally placed directly onto a prepared structural concrete slab. The crack resistance of the terrazzo was based primarily on two functions. First, the epoxy terrazzo formulations were extremely high in tensile strength and second, they did not contain excess water that leads to shrinkage cracks or volume change during the curing process.

Epoxy formulators introduced flexible epoxy membranes that are installed at a nominal 40 mils. Thickness and engineered for high tensile strength and high elongation, relative to the epoxy binder matrix. These membranes have become industry standard for crack detailing and, in some cases, full slab coverage prior to the installation of the thin-set epoxy terrazzo.


Concrete has been the standard flooring substrate in the commercial construction industry for many years. The concrete industry has developed many industry guidelines and recommendations to minimize cracking.

While there have been many improvements in mix designs, placement techniques and industry standards, the concrete industry has not perfected the placement of slabs without cracks.

Cracks in concrete are a result of any number of issues, including volume change during the curing process, load deflection, settlement cracks and cracks induced from thermal stresses, which are typically due to non-climate-controlled environments during the construction process. While shrinkage cracks, which account for most concrete cracking, become static once the volume change from curing is complete, any crack has the potential to become a dynamic, moving crack under thermal and load movement stresses. To accommodate dynamic loading, slabs should be designed for maximum deflection of L/360. Cracks should be filled with low modules epoxy. Not flexible epoxy membrane.

Tile/Stone type divider strips are not to be used in either cement or epoxy terrazzo installations.


The details contained herein provide general information to use as a starting point for detailing site conditions that frequently occur on epoxy terrazzo projects.

They represent generally accepted practices of terrazzo contractors and suppliers across the United States under typical circumstances. These details do not replace the direction or advice of an architect or engineer regarding a specific project or for specific project conditions. Architect or engineer must specify movement joints and show location and details on drawings.

It is not the intent of this guide to make movement joint recommendations for a specific project. For your particular project(s), you should consider contacting an NTMA Contractor Member in your area to discuss details that may be most applicable for a given circumstance/location.

To mitigate cracking and curling in concrete at epoxy terrazzo areas follow recommendations in ACI 360R-10.

Terrazzo divider strips must precisely follow the concrete joint – even if crooked, to mitigate cracking in the terrazzo system.

Terrazzo divider strips are not flattening or leveling devices. They must adhere tightly to the concrete.

Tooled edges on concrete joints are not to be used at areas to receive epoxy terrazzo.

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