Thin Set Epoxy Terrazzo vs. Sand Cushioned Cement
A Features Comparison
| Property | Morricite Epoxy (Thin Set Epoxy) | Sand Cushioned Cement (SCC) | Advantage |
| Thickness | 3/8” | 2 3/4” to 3” | Even |
| Comments: Actual thickness of cement terrazzo is only 1/2” thick installed over a low strength cement bed. Epoxy performance properties exceed cement in every category; both systems are listed by NTMA with a minimum life expectancy of 40 years. | |||
| Weight/SF | 4 1/2 lbs. | 30 lbs. | Epoxy |
| Comments: Heavy dead loads of SCC systems require beefed up structural designs. | |||
| Depressed Structural Slab | No | Yes | Epoxy |
| Comments: Depressed slabs require additional design and detailing to match elevations often requiring leveling beds under other finishes. The additional costs of designing and building depressed slabs is often overlooked in evaluating costs vs. epoxy. | |||
| Slab Flatness/Levelness | 3/8” thickness makes epoxy more sensitive to slab thickness. | Isolation sand and poly in addition to 2” cement under bed give SCC the clear advantage over thin set. | SCC |
| Comments: Thin set systems have more problems with 1/4” thickness. Most decorative epoxy terrazzo is being installed at a minimum of 3/8” thickness. | |||
| Compressive Strength | 12,000 psi - ASTM D695 | Cement 4,800 psi - 7,000 psi Bed 1,800 psi - 3,000 psi |
Epoxy |
| Comments: Variations in cement result from cement type and mix designs. Epoxy is typically 2-3 times the strength of SCC topping and 4-7 times the strength of the SCC underbed. | |||
| Point Loading | Epoxy | ||
| Comments: A chain is as strong as the weakest link, in this case, the cement underbed. Weak underbed in SCC provides lower resistance to point loading when compared to epoxy. | |||
| Tensile Strength | 4,800 psi - ASTM D838 | 400 - 600 psi *Extrapolated from history of cement based topping approx. 10% of compressive strength | Epoxy |
| Comments: Higher tensile strengths will help resist cracking, and provide greater abrasion resistance. | |||
| Volume Change During Curing | 100% solids, minimal shrinkage | Water hydrated cement systems have excess water which causes volume change during cure. | Epoxy |
| Comments: Water hydrated cementitious toppings require additional water beyond the amount necessary to hydrate cement. This excess water leaves the systems initiating volume change that must be designed into the topping. | |||
| Strip Spacing | 15’ to 20’ O.C. or to the spacing of control joints | 4’ O.C. | Epoxy |
| Comments: The strips 4’ O.C. set in the underbed provide control joints to accommodate the volume change in the cementitious terrazzo. | |||
| Strip Geometry | Unlimited in geometric shape of strips. Epoxy binder is 100% solids - the wet volume is the same as the dry volume allowing for uniform cure in any shape without curing related shrinkage cracking. | Squares and Rectangles work best. Irregular shaped panels have greater tendency to crack due to differential cure of cement terrazzo. All strips must interconnect. | Epoxy |
| Comments: Epoxy allows for greater distances between strips and greater flexibility in design should complicated layouts be desired. | |||
| Isolation Membrane | MasterFlexTM Flexible Epoxy Isolation Membrane is bonded to structural concrete slab to accommodate up to 1/8” movement. | Poly and Sand SCC are isolated from the structural concrete. | Even |
| Comments: While isolation of SCC exceeds adhered epoxy systems, the volume change, low tensile strength and lower flexural modulus for cement based systems equalize performance. | |||
| Reflective Cracking | Epoxy systems do not have curing shrinkage and do have much greater tensile strength and modulus of elasticity; however, they are bonded to slab. Flexible epoxy membranes are now available to provide comparable resistance to reflective cracking as the SCC systems. | SCC is isolated from slab with layer of sand and polyethylene film. This in conjunction with mesh reinforced cement bed allows the SCC to act as an independent structural slab. | Even |
| Comments: Epoxy systems have higher performance properties of tensile, modulus of elasticity and volume change; however, SCC systems are totally isolated and reinforced with mesh and strip/control joints. Both systems have performed well in minimizing reflective cracking from slabs. | |||
| Matrix Color Range | Unlimited - Will computer match any paint chip. | Limited to cement pigmentation process. Cement pigments must be mixed in dry and are typically limited to 2 lbs. per bag of cement. They are affected by variations in water/cement ratios. | Epoxy |
| Comments: Morricite epoxy can be formulated in manufacturing controlled environments to meet any color desired. Formulation consistency and factory quality control give epoxy the clear advantage. | |||
| Color Consistency | Epoxy colors are extremely uniform due to batch to batch formula consistency. Formulas are controlled with precision ingredient weighing using load cells and colors are factory verified in QC checks after manufacturing. | Cement based coloring systems are field added and are very dependent on consistency of mix design, temperature, curing conditions, and water cement ratios. | Epoxy |
| Comments: Epoxy color consistency have been demonstrated for years. The color batching has been removed from the field by the mixing mechanic and completed in a laboratory-controlled environment. | |||
| Special Aggregates and Features | Epoxy terrazzo is frequently installed utilizing special aggregates including glass, plastic, mother of pearl and metal. Epoxy also bonds well to various types of metal inserts. | SCC does not accept special aggregates or metal well, due to their dense surface, the lack of bond achieved with cement, and the shrinkage during cure. | Epoxy |
| Comments: Epoxy terrazzo offers the maximum in design flexibility when utilizing special aggregates. | |||
| Pre-Cast | Yes. Epoxy works well in wet environments or where sanitary conditions are important. Can be more easily used in odd shapes, angles and thinner sections. Stair treads and risers are caps, not structural. | Yes. In most tread riser details are structural when made from cement due to the thickness required to precast. | Even |
| Comments: Cement Pre-cast can be used very successfully with epoxy; however, choose the cement precast colors first and match epoxy to cement, not visa versa. | |||
| Installed Cost | While epoxy binder is more expensive than cement counterpart, thickness, production, and logistics when compared to SCC far outweigh higher material costs. | $1.00 to $3.00 /SF more. The cost difference increases in fast track projects or where storage is a problem due to logistics of physically moving tons of chips and cement. | Epoxy |
| Comments: This lower cost of epoxy does not include the additional structural requirements and the additional formwork to build depressed slabs in specific terrazzo sections. | |||
| Maintenance Costs | $.46 /SF | $.58 /SF | Epoxy |
| Comments: Independent maintenance have documented the lower maintenance costs of epoxy vs. cement due to density of the surface, resistance to staining, and the higher strength for resistance to loads and stress at strip locations. | |||
| Preparation Considerations | For slab on grade applications, epoxy terrazzo requires a good vapor barrier under the slab and proper moisture conditions during installation. The substrate must be well prepared prior to installation. | SCC is forgiving to project moisture conditions. Since the system is separated from the substrate with a poly sheet, surface preparation requirements are minimal. | SCC |
| Comments: Like other types of bonded flooring including wood, carpet and vinyl, epoxy terrazzo requires more precise project conditions related to underslab vapor barriers and concrete surface preparation. While SCC will not bubble due to negative side moisture transmission, it is sensitive to color shading and mineral deposits along strips. | |||
| Installation Complexity | Epoxy terrazzo installations are much simpler since they are directly bonded to the slab and cure more easily. | Sand cushioned terrazzo requires a multi-step pouring process which is very labor intensive. In particular, the pulling of the bed and setting of strips requires skilled labor. There are also longer waiting times to grind - the terrazzo contractor requires each area longer. | Epoxy |
| Comments: The preparation and pouring of sand cushioned terrazzo is much more complex and labor intensive than epoxy terrazzo. | |||
| Speed of Construction | Epoxy terrazzo requires less manpower while allowing greater production rates. Epoxy can be ground the next day, if necessary. | SCC usually requires second crew just for screeding and placement of the underbed. Also, must wait 5-7 days prior to grinding cement. First grinding step of cement must be wet ground creating more slop as opposed to epoxy which can be dry ground. | Epoxy |
| Comments: In today’s world of fast track, rapid paced construction, speed of installation is critical. Epoxy systems can be poured and turned over to other trades prior to grinding. Cement systems must be ground and sealed to protect from staining problems with other trades. | |||
| Availability of Skilled Installation Labor | Epoxy terrazzo can be provided in all US geographic markets. Due to the lower installation complexity, it is easier for major contractors to travel to competitively bid large projects. | It has become difficult to get SCC cost effectively installed in several major markets, especially with the retirement of 2nd and 3rd generation skilled Italian labor. | Epoxy |
| Comments: Due to the substantial growth as a percentage of total installations of epoxy terrazzo vs. SCC, and the decline of skilled labor to install the SCC beds and strips, it is much easier to get terrazzo installed in many US markets. | |||
| Storage Space | A truckload of epoxy will cover 14,000-16,000 SF of finished terrazzo flooring. | A truckload of SCC will yield only 1200-1500 SF of finished terrazzo flooring. | Epoxy |
| Comments: Large SCC jobs have 9-12 times the volume of sand cement and marble chips than thin set epoxy. On many sites this will create storage logistical problems for the GC and the owner. | |||