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  • Writer's picturebradhedges

Terrazzo Overlays Over Existing Flooring

Updated: Sep 29, 2020

In today's post we are going to discuss the ability to overlay an existing floor finish with epoxy terrazzo. A flooring upgrate is one of the main areas owners consider when renovating their spaces. It's amazing to see the difference a floor can make.

One of the many benefits of specifying epoxy terrazzo is the ability to overlay certain existing hard surface flooring. We want to avoid fragile tiles such as ceramic or porcelain, along with any other soft flooring that would need to be removed along with any setting material or adhesive. Good candidates to consider a terrazzo overlay would be existing terrazzo, a natural stone floor or even quarry tile. The next step is to get your local terrazzo representative or contractor to visit the project to inspect the existing floor for soundness to ensure the existing flooring will be an acceptable substrate to go over. If any unsound areas are located these areas should be removed full depth and filled with an appropriate fill material, such as epoxy and sand.

Moisture Testing

Many of the acceptable flooring finishes are set using a mortar bed. These mortar beds can retain a lot of moisture. It is imperative that moisture tests be performed. We recommend ASTM-2170 in situ probe test. If readings are below 80% relative humidity no moisture vapor control system is necessary, however, if readings are 80% or greater a moisture vapor control system such as Terroxy Moisture Vapor Treatment should be applied after surface preparation.


The preparation of the floor requires removal of all foreign matter such as coatings, waxes and sealers. This should be done by terrazzo grinding machines abrading the existing surface or by shot blasting. Next if you are going over a natural stone tile the grout joints should be filled with epoxy.

Flexible Crack Membrane

Once the floor is cleaned and any moisture issues are dealt with it is essential to use a liquid applied membrane such as Terroxy Iso-Crack Membrane. The membrane prevents any existing divider strips or cracks from mirroring or cracking the new terrazzo. Any cracks in the existing floor should be stabilized with rigid epoxy prior to applying the crack membrane.

If the existing strip pattern is used in the new terrazzo, a crack membrane over these strips may not be required.

Flooring Transitions

Since we are putting a new floor finish over top of an existing floor there will be some transition areas that will need to be addressed. These are primarily at door thresholds and elevators. The new thin-set epoxy terrazzo has a total finished thickness of just ⅜” or even as thin as ¼”. The additional height elevation in these areas can be problematic. However, there is a simple fix. We simply remove the existing flooring approx 2-3 feet back from the transition area. Then infill the area while creating a slight slope down to ⅜” below the original transition height.

This allows the terrazzo contractor to install a flush transition at the original transition height permitting for proper functioning of doors. The mild slope is nothing to be concerned with; it is hardly noticeable with the finished product.

Time and Money

The biggest advantage of a terrazzo overlay is the time and money saved. Typically, removal of the existing flooring is a costly, time consuming and disruptive process. Save weeks of time in the construction schedule and keep money in the owners pocket or allow them to use those resources for other important features in the project. At Charleston International Airport, some 90,000 square feet of epoxy terrazzo was installed successfully directly over brick pavers. The savings for leaving in the old floor was estimated at over $1 million, according to John Wingo, senior project manager with the David Allen Company of Raleigh, NC. Not to mention all the material that is diverted from going into a land fill.


Owners will need to consider the best phasing for their project and budget. Some owners will close off the entire area to be renovated permitting access to the full space. This is a great option if your facility permits. However, that is not always feasible for building owners renovating an occupied space. In these cases, the project will be sectioned off and phased. The downside is this hinders the terrazzo installers production and will result in a more costly and longer installation duration. We are happy to connect you with a qualified terrazzo installer that has experience with terrazzo overlays to assist with phasing recommendations.

Other Considerations

It can be helpful to take a core test to determine the thickness of the existing floor substrate. We always recommend an independent certified third party to perform moisture testing.

We hope this helps you better understand the terrazzo overlay process.

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