Slippery Rock Gazette

Bob Murrell 

Stone Restoration

Photos provided by Bob Murrell

The use of terrazzo dates back thousands of years and it is one of the most popular flooring surfaces in the USA today. You’ll find it in schools, hospitals, airports, and even in residential settings.            

Terrazzo originated as a recycling of discarded marble pieces from paying construction projects. Artisans would collect the marble pieces left over, take them home, and then place them in a clay product on terraces around their homes. These surfaces became very popular because of their beauty and durability.

Once the electric motor was in play in the early 1900s, the use of terrazzo really took off. Typical poured cementitious terrazzo was and is a combination of layers consisting of concrete, then sandy concrete, and finally a cement-based layer (matrix) in which the chips are added. The final layer is pressed with a weighted roller. 

Newer polymer-based terrazzos are also very popular as they can be thinner, more resilient to cracking, and less susceptible to penetration or attack from foreign contaminants. There is a wider variety of colors and they can be much more vivid. Modern polymer terrazzo is mostly epoxy based. It does have it’s limitations, such as not being suitable for exterior applications.  

Chips can be the typical marble, quartz, glass, or most any durable yet grindable item the artisan chooses. Cements can be pigmented for a colorful display. Metal divider strips are used to break up the colors and also as joints. Normally zinc (silver colored) and brass (gold colored) strips are used but aluminum and other materials are also used occasionally.

Once cured, terrazzo was originally ground in place using mules to drag large sandstone or similar stone blocks. This would help expose the chips and make for a smoother surface. Today, large industrial multi-headed machines are used to grind the surface smooth and more evenly expose the chips.

The grinding process typically consists of a coarse grinding process starting at about 46 grit, then 70 grit, and finally continues through about 100 grit or so. This can be either a wet grinding process or dry grinding process. Both have their advantages and disadvantages.  

Once the terrazzo has been ground smooth and the chips evenly exposed, a sealer coating of high solid content is normally applied. This gives the terrazzo a shine and some resistance to foreign contaminants. Eventually, when the original coating has begun to wear, floor finish and wax are applied by the building service contractors. At this point the terrazzo is treated like VCT and the strip and coat process becomes ongoing.

New maintenance techniques have been developed to improve the appearance of the terrazzo and lower routine costs. Natural polishing (like marble) of terrazzo is now an accepted procedure in many circumstances. It also reduces the use of harsh chemicals, helping keep the ongoing maintenance more environmentally sound.  

The natural polishing process is actually quite easy. The original grind to about a 100 grit is continued at a 220 grit level and then followed with a 400 grit and an 800 grit for most cementitious terrazzo. Epoxy terrazzo may require honing to a finer level –1800 grit or even higher. Of course, with years of stripping and waxing, the process may require starting at a coarser grit level, so a test area should be submitted for approval before starting the general application. 

Finally, just like when polishing marble, polishing is achieved using stone polishing compound or 5X. This is typically done with slow speed swing machines and a natural hair pad. In some cases optional use of a spray crystallizer and #0 steel wool may be necessary to achieve a higher degree of clarity or reduce what I call alligator graining (where the chip is slightly exposed at a higher level than the matrix).   

Routine maintenance consists of dust moping, damp moping or auto-scrubbing with either a quality stone soap or neutral cleaner, and simply re-polishing the traffic lanes as required (typically quarterly for commercial applications).  

Natural polishing of terrazzo helps the floor look better and healthier and at the same time costs less to maintain. It no longer requires stripping and recoating with harsh chemicals, which reduces labor costs significantly, doesn’t yellow or discolor, and won’t scuff or show heal marks. It is what I call a “duh, no-brainer” system. 

Other more economical methods of achieving a natural look without coatings are available too. Use of the diamond impregnated pads can, in many cases, get a good look and the terrazzo would still require less maintenance than coatings, as would most any honed material.

There are other types of terrazzo flooring, including precast terrazzo tiles, which are very popular. These are typically either honed or polished at the factory and installed by thin set method. With precast terrazzo tiles the installation becomes more like a stone floor in that it will contain grout lines and therefore, lippage. Most of these can be leveled and naturally polished, too.

In some cases a coating may actually be desired on cementitious terrazzo such as a cafeteria serving line or a vinegar and pickle aisle in a grocery store. I find the newer concrete guard products work very well for this application. Also, many contractors advocate the use of lithium densifiers on cement-based terrazzo. This would depend on the actual terrazzo.

By no means have I covered every topic related to terrazzo installations. Do your research and submit a test area for approval on each project. And of course as always, it is best to work with a knowledgeable and qualified distributor of quality products and excellent technical support to help assure your project success. 

Bob Murrell has worked as a supplier of products and technical support to the natural stone industry for over 35 years. He has written numerous articles for various trade publications and has also trained thousands of contractors over the last 25 years.