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Epoxy Terrazzo System Cross Section

Updated: Jan 7, 2021

In today's post we are going to overview the components and functions of the thin-set epoxy terrazzo system.

Let's start with the substrate and work our way up through the different components.


In commercial construction, concrete is the most common flooring substrate and is the preferred substrate for epoxy terrazzo. However, we are not limited to a concrete substrate. Additionally, epoxy terrazzo may be installed over metal, wood substrates or even existing flooring systems. Proper substrate preparation is critical for all substrates. In the terrazzo world a shot blasted substrate is the preferred method of surface preparation. Surface prep results should yield an ICRI Guideline No. 03732 Concrete Surface Profile of 3-5.

ICRI Concrete Surface Profiles Chart
ICRI Concrete Surface Profiles

This will provide a sound concrete surface free of laitance, glaze, efflorescence, curing compounds, form- release agents, dust, dirt, grease, oil and other contaminants incompatible with terrazzo.

Shot Blasted Concrete Profile Rows
Shot Blasted Concrete

The terrazzo installer will then repair or level damaged and deteriorated concrete using a resinous fill material.

Moisture Testing

Next the terrazzo contractor will need to verify that the concrete substrate is visibly dry and free of moisture. Our preferred method of moisture testing is ASTM 2170 (determining relative humidity in concrete slabs using in situ probes). Proceed with installation only after substrates have a maximum relative humidity measurement reading less than 80%. If relative humidity measurement reading is greater than or equal to 80% this brings us to the first component and one of the most important components of the epoxy terrazzo system: Terroxy Moisture

Vapor Treatment. This will be required when readings are 80% RH or greater and shall be applied to terrazzo substrates according to the manufacturer's product data sheet. This material has a low viscosity and will seal off the capillaries in the concrete to protect the terrazzo topping from excessive moisture vapor transmission. Failure to properly apply a terrazzo mitigation system will result in failure of bond and blisters and de-lamination. Don’t worry we’ve got you covered, Terroxy’s moisture mitigation system works very well and has a substantial record of successful installations to the tune of 20 million sf!

Terroxy Primer

Next the terrazzo contractor will apply terroxy terroxy primer. The product is designed to enhance the bond to the concrete slab by providing excellent filling and sealing of concrete. Like Terroxy Moisture Vapor Treatment, Terroxy Primer is quickly applied using a roller.

Terroxy Iso-Crack Membrane

Flexible Epoxy Crack Membranes are another important component of the epoxy terrazzo system. These membranes are designed to suppress reflective cracking in terrazzo topping. As a specifier you have two options for specifying this product.

Pre-fill Crack with Rigid Epoxy then Cover with Flexible Crack Membrane. Isolated Coverage Shown
Terrazzo Crack Detail Isolated Coverage

Option 1: Membrane application for Isolated cracking. Contractors will only address cracks that show in the substrate after surface preparation. When specifying it is important to outline an approximate coverage, typically this is between 5-10% of the total terrazzo square footage in lineal feet. For example, if you have a 10,000 sf terrazzo project the contractor would allow for between 500-1000 linear feet of crack detailing.

Pre-fill Crack with Rigid Epoxy then Cover with Flexible Crack Membrane. Full Coverage Shown
Terrazzo Crack Detail Full Coverage

Option 2: Membrane application for extensive cracking or crack prevention. In this case, the crack membrane will be applied beneath all terrazzo surfaces. Typically, option 1 is specified unless you have light weight concrete or may be doing a terrazzo overlay over an existing flooring. When applied using option 2, Iso-Crack membrane will also act as a positive side waterproofing membrane.

Regardless of the specified option, the crack detail will be the same. Cracks are stabilized using rigid epoxy then the flexible crack membrane is applied overtop at 40 mils thickness.

Architectural Enlarged Detail Terrazzo Crack Treatment
Terrazzo Crack Detail Isolated Coverage

Architectural Enlarged Detail of Terrazzo Crack Treatment
Terrazzo Crack Detail Full Coverage

Optional Acoustical Membrane

When working with hard surfaces some clients may be concerned about sound transmission between floor to floor. If your client is concerned about this Terroxy Acoustical Membrane is a great option. Terroxy Acoustical Membrane utilized the Terroxy Iso-Crack Membrane as a binding agent along with a mixture of ground up recycled rubber sized to about 1/8" granule size. This mixture is then trowel applied to the substrate to provide an acoustical membrane and will reduce the IIC rating by a delta of 13 while adding an additional 40% of recycled content to the system.

Divider Strips

The divider strips are then placed according to the specified patterning. The strips are set with epoxy rather than mechanically attached. There are multiple materials and thickness gauges to select from. More on terrazzo divider strips in this blog post. It is also important that any concrete joints are properly addressed at this point. We recommend following NTMA Technical Bulletin T24. Feel free to contact us for assistance with this technical topic.

Terrazzo Topping

After all the proper preparation has been completed the terrazzo contractor is ready to pour the terrazzo topping. Here the Terroxy Epoxy Matrix is used as the binding agent to bind the aggregates together and also bond the system to the substrate.

Resin Mixing Terrazzo
Adding Resin

This is a 5:1 mix two component mix. 5 gallons of resin to 1 gallon of hardener and typically contains 180-200 lbs of aggregate.

Mixing Terrazzo Chips
Adding Aggregate

Once thoroughly mixed the terrazzo contractor will hand trowel the terrazzo mix in place, hence the name poured in place terrazzo or cast in place terrazzo.

The epoxy terrazzo topping will be troweled to a total system thickness of ⅜”.

Hand Trowel Poured in Place Cast In Place Terrazzo
Hand Troweled in Place Terrazzo Flooring

Once the epoxy terrazzo mix has been placed it will typically cure within 1-4 hrs depending on temperature and relative humidity. Curing can be accelerated or retarded using different hardening agents.

Grind and Polishing

After the terrazzo has cured, the terrazzo contractor will start the grinding and polishing process. This consists of a rough, medium and fine grind.

Ground and Polished Terrazzo Image
Unground Terrazzo on Right. Rough Ground Terrazzo On Left

For a standard finish terrazzo 120 grit is the level of final polish. More on understanding the grinding and polishing process in this post. At this point the terrazzo system will also be grouted using the epoxy matrix to fill any voids or fissures exposed during the grinding process.

Application of Topical Sealer

After the grinding and polishing process is completed and the floor has been thoroughly cleaned and dried the terrazzo contractor will apply 2 coats of a topical sealer. The sealer is multipurpose in providing a protective coating to seal any porous aggregates and also provides the final finish of the terrazzo floor. You can specify matte, satin, gloss or high gloss sealers depending on your finish preference.

Gloss Terrazzo Finish
Gloss Terrazzo Finish

We hope this helps you have a better understanding of the epoxy terrazzo system. As always, please feel free to contact us if you have any questions. Thanks for reading.

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