Updated: Apr 7, 2020
In our last blog, we discussed Terrazzo Divider Strips. In this post, we’ll do a comprehensive analysis of the different binder materials epoxy vs cement terrazzo and compare the different systems.
Different Cement Terrazzo Systems There are 5 different cement terrazzo systems:
Sand Cushioned Terrazzo
We’ll break each of them down for your here:
This system is a ½” cement terrazzo topping bonded directly to the slab. If you live in the Southeast United States you are likely familiar with the Publix grocery chain. All their slab on grade stores are using Monolithic terrazzo. Each store is approx 35,000 sf, one color, which typically installs for approx $8 per sf. This is the most economical terrazzo system available. However, there are some downsides. Monolithic Terrazzo is dependent on the quality of concrete substrate for cracking and flatness. If the concrete cracks it will crack the terrazzo topping. Further, all concrete joints must be honored up through the terrazzo topping. This system may only be specified for on grade or below grade applications, no elevated slab.
This system is very similar to the Monolithic system with the addition of a sand cement underbed, similar to a mud bed you’d use when setting natural stone. The underbed absorbs flatness variation in the concrete slab so it creates less dependance on the concrete slab for flatness when compared to the monolithic system. The underbed has a thickness of 1-¼” - 1-¾” and is then topped with the same ½” cement terrazzo topping so total system thickness will be 1-¾” - 2-¼” and will require the structural slab to be recessed. If the slab or underbed crack the topping will crack. All concrete joints must be honored up through the terrazzo topping. Sand Cushion Terrazzo
Sand Cushion Terrazzo is also similar to the bonded terrazzo system. This system was designed the industry's first attempt to minimize cracking and provide a very flat terrazzo floor. Sand Cushioned Terrazzo uses a light dusting of sand and an isolation membrane, typically 15 lb felt paper or polyethylene sheeting, to break the bond between the structural slab and the underbed. This way if the structural slab cracked in the horizontal plane, it was isolated and did not reflect through the system. Further design included a thicker underbed and more divider strips to relieve the terrazzo system. Cement matrix topping underbed with wire reinforcing, isolation sheet, and sand layer system for interior floor use. This is the best cement system. Epoxy Terrazzo A nominal ⅜” thick epoxy resin matrix veneer placed upon a level concrete slab. It can be specified with glass, plastic or granite aggregate in lieu of marble to provide vivid color and optimal chemical resistance. This is the best thin-set system.
Epoxy vs Cement Terrazzo Systems Now that we’ve defined Epoxy Terrazzo and Cement Systems let’s start differentiating them. Below are the 10 key points:
Strip Spacing & Geometry
Speed of Construction
Color Range and Consistency
Moisture and Breathability
Interior vs Exterior
Epoxy is a much stronger and ultimately more durable material than cement. Below are specifics on Physical Properties. Regardless of the cement system epoxy is far superior.
Epoxy Terrazzo will have a Compressive Strength of nearly 14,000psi. Thus allowing epoxy terrazzo to be subjected to heavy loads. Whereas the cement terrazzo only achieves 3-4000psi. Epoxy is known to be three times stronger than cement. According to the National Terrazzo & Mosaic Association, Epoxy is the most versatile, the strongest and the least susceptible to scratching, fading, cracking or staining.
How long does it take to break? Well, for epoxy it is 10x stronger than cement. At 4800 psi, the terrazzo is now resistant to abrasions and cracking. Whereas cement terrazzo will only achieve 480 psi. How awesome is that?
Flexural Strength Lastly, epoxy terrazzo has a much greater flexural strength than cement terrazzo. Epoxy terrazzo flexural strength calcs out at an impressive 4500 psi. This allows it to be used in multi-store applications and absorb movement that would crack a cement terrazzo system. Cement terrazzo flexural strength is around 400 psi. Therefore we never recommend using cement on elevated slab applications.
Epoxy terrazzo wins here again as all cement systems use a porous binder. Cement is a porous material thus making the material very susceptible to staining. Whereas the epoxy is an impervious material and has excellent stain resistance. This is one of the main reasons you see epoxy terrazzo used so frequently in medical applications. The impervious nature of the material offers optimal sanitary conditions.
Strip Spacing & Geometry
According to ™ Supply, epoxy is unlimited in geometric shapes of strips. For cementitious systems, squares and rectangles work best. Cementitious terrazzo with irregular shapes be problematic since it has a tendency to crack due to differential cure of cement terrazzo. Epoxy terrazzo requires fewer control joints offering more design flexibility. Cement terrazzo will also have more frequent joint spacing because we must honor any concrete joints with a divider strip. Epoxy terrazzo has the ability to use a crack membrane to span some concrete joints thus allowing for larger panel sizes than any of the cementitious terrazzo systems.
With Epoxy terrazzo you can use any special aggregates, such as glass, mother of pearl, shell, metals, plastic or natural stone. On the other hand, cement terrazzo systems do not accept special aggregates well due to their dense surface and curing shrinkage. If these special aggregates are used they are likely to be problematic and dislodge from the system. Some cement additives do exist to help with bonding and can permit some of the specialty aggregates. Furthermore, cement systems should avoid smaller size aggregates as they can easily dislodge or compromise the structural integrity of the system. Whereas the epoxy binder has a tenacious bond allowing it to any size aggregate.
Volume Change and Shrinkage It’s common during cement terrazzo installation for cracking to occur due to the volume change that occurs from curing. All cement systems are water hydrated so they must have excess water because shrinkage occurs mostly due to the evaporation of the mixing capillary water. Whereas Epoxy terrazzo is 100% solids, with that we assure you that it has no volume change and thus is more crack resistant. Speed of Construction In construction, we all know that speed is one of our main priorities. Epoxy terrazzo has a faster cure time compared to cement. Epoxy can cure as quickly as 90 minutes. This allows epoxy terrazzo systems to be poured and turned over to other trades prior to grinding. On the other hand, cement terrazzo systems take 3-4 days to cure before grinding. Then must be polished and sealed to protect from staining problems with other trades. Epoxy terrazzo requires less manpower while allowing greater production rates and construction flexibility. Cement terrazzo systems with underbeds add additional cure time and material logistics of handling extra sand and cement.
Color Range & Consistency
Let’s talk about the color range. With cement-based coloring systems, consistency is key. Mix design, temperature, curing conditions, and water-cement ratios must be consistent. Below we’re showing you some of the colors that can be achieved with Cement terrazzo as well as what happens with an inconsistent mix.
So how about Epoxy terrazzo? According to ™ supply “Epoxy colors are extremely uniform due to batch to batch formula consistency. Formulas are controlled with precision ingredient weighing using load cells. All colors are factory verified and QC checks are performed after manufacturing. No longer do we mix batch to batch in the field, mass batches are created and completed in a laboratory-controlled environment. Thus arriving at beautiful, consistent and constant resin colors.” Epoxy also permits for more vivid colors and can be easily matched to any paint or pantone color.
Maintenance Costs Independent maintenance studies published by the NTMA documented the lower maintenance costs of epoxy vs. cement due to the density of the surface. Epoxy is 20% less compared to Cement terrazzo maintenance costs. Bacteria growth and staining are not an option to epoxy since it is impervious. Further, epoxy terrazzo is much more durable than cement terrazzo. Cement is porous so you can expect to perform more maintenance. Installed Costs Epoxy terrazzo installed costs are 20% more than monolithic cement terrazzo. However, epoxy terrazzo can be installed for equal to or less than any other cement terrazzo systems. Why is that? ™ supply said “Thickness, production, and logistics of cement terrazzo far outweigh the higher epoxy material costs. Cement systems using under beds cost increases with the size of projects due to the logistics of moving/handling tons of additional material.”
Labor Considerations Cement terrazzo is a more technical installation. Cement terrazzo may be restricted in certain regions due to the limited availability of skilled labor required for installation. Regardless of terrazzo system we recommend using an NTMA Contractor for best results.Further, cement terrazzo typically ties up a jobsite longer for other trades. The majority of terrazzo contractors today prefer to install and are more familiar with epoxy terrazzo.
Moisture and Breathability All cement terrazzo systems have the leg up here. It's a porous material so it will let moisture breath through the system. However, excessive moisture can show itself at divider strips causing them to darken. Epoxy terrazzo is an impervious material so it does not breath. This is problematic if the concrete presents high moisture content, 80% Relative Humidity or 4 or higher with a Calcium Chloride test. If it is applied without a moisture mitigation system it will fail causing the floor to blister or bubble and will delaminate as shown in images below. Don’t worry simply specify Terroxy Moisture Vapor Transmission and be covered up to 99% RH.
Interior vs Exterior Epoxy terrazzo is intended for interior applications only. Whereas cement terrazzo can be used in either application.
Hopefully, this was helpful. So what do you think is best for your project? If you have more questions, feel free to send us a message. We’re excited to serve you! Please do check out our other blog entries! Read more: Poured-in-Place Terrazzo vs Tile Terrazzo Terrazzo: The Beginning