What Is Shellcrete?
The complete guide to shell-aggregate concrete — composition, names, benefits, and specs.
Defining Shellcrete
Shellcrete is a decorative concrete material incorporating crushed shell aggregate into the mix. It is known by several names:
- Shell Tabby — the historic colonial American term
- Tabby — shortened version used in the American Southeast
- Coquina Concrete — referencing coquina limestone of coastal Florida
- Washed Shell Concrete — a modern descriptor based on the finishing process
Shellcrete is installed using white Portland cement, fine sand, and locally sourced crushed shell aggregate. The finished surface evokes walking on the beach without sharp shells underfoot.
Durable
Shell aggregate enhances resistance to wear, cracking, and erosion. Strength improves after curing.
Slip Resistant
Natural shell texture provides traction — ideal for wet pool decks, walkways, and coastal entry points.
Eco-Friendly
Repurposes shell byproducts from seafood industries, reducing landfill waste and demand for mined aggregate.
Heat Reflective
Reflects sunlight and absorbs less heat than standard concrete — keeping surfaces cooler underfoot.
Coastal Aesthetic
Unique shell patterns create a one-of-a-kind surface complementing any coastal environment.
Low Maintenance
Resistant to stains, mold, and mildew. Seal once a year. Pressure washing keeps it looking new.
Mix Composition
- Base: White Portland Cement (Type I/II)
- Aggregate: Crushed local shell (oyster, clam, or mussel)
- Sand: Fine-grade clean sand
- Optional: Integral pigment admixtures for custom color
Installation Specs
- Thickness: 5/8 to 3/4 inch standard topping
- Minimum pitch: 1-1/2 inch per 10 feet
- Sealer: Applied after cure; annual resealing recommended
- Control joints: Saw-cut per industry standards
Substrate Requirements
- Existing slab must be structurally sound and crack-free
- Surface scarified to minimum 1/16 inch average depth
- Clean, dry, and free of oils or contaminants
- Control joints aligned with existing substrate
Best Applications
- Pool decks and pool surrounds
- Residential and commercial driveways
- Patios, lanais, and outdoor living areas
- Walkways, paths, and entry areas
- Formed stairs, planters, and fire features
Frequently Asked Questions
Is Shellcrete the same as coquina?
Coquina is a naturally occurring limestone made of compressed shell and sand. Shellcrete is man-made concrete incorporating crushed shell aggregate into a Portland cement mix. While similar visually and regionally, they are distinct materials.
How durable is Shellcrete compared to regular concrete?
Shellcrete is generally more durable for outdoor surface applications. Shell aggregate creates strong adhesion with cement paste, and tensile and flexural strength continue improving over time, particularly after 90 days of curing.
Can Shellcrete be installed over existing concrete?
Yes. If the existing slab is structurally sound, Shellcrete can be applied as a topping at 5/8 to 3/4 inch thickness. The surface must first be scarified to a minimum 1/16 inch depth to ensure proper adhesion.
What maintenance does Shellcrete require?
Shellcrete is low-maintenance. Annual cleaning and resealing is recommended to preserve color, texture, and surface protection. Pressure washing is safe and will not damage the finished surface.
Is Shellcrete LEED eligible?
Yes. Through its use of local reclaimed shell aggregate, low-VOC finishes, and high material durability, Shellcrete can support LEED certification goals. Consult your project LEED certifier for specific point eligibility.
What types of shells are used?
The most common shells are oyster, clam, and mussel. Oyster shells produce ivory and cream tones, clam shells produce warm beige and tan, and mussel shells create cool blue-gray finishes. Mixed blends are also available.
Can Shellcrete be used indoors?
Yes. Shellcrete works well for interior flooring and feature surfaces in coastal-style interiors. Proper sealing is important to protect against moisture and staining indoors.
How long does Shellcrete last?
With proper installation and annual sealing, Shellcrete surfaces typically last 20 to 30 or more years. The material is highly resistant to heat, humidity, salt air, and UV exposure.