Tabby, coquina, shellcrete: four names for one surface

If you have been getting quotes for a shell-flecked concrete deck, you have probably been given four different words for what is broadly the same idea. It is genuinely confusing, and the confusion is not accidental — some of it is regional, some of it is historical, and some of it is marketing.

Tabby

The oldest of the four and the only one with a real history behind it. Tabby is a building material used along the Georgia, South Carolina and north Florida coast from the 1500s onward: oyster shell, lime burned from oyster shell, sand and water, poured in lifts into wooden forms. Whole houses and fort walls were built from it, and a number of them are still standing.

Historic tabby used lime, not Portland cement, which had not been invented. So when a modern contractor says "tabby", they mean a surface that references the look. It is not the same material, and anyone claiming to build in authentic tabby is either doing historic restoration or being loose with the word.

Coquina

Coquina is a rock: a soft, porous limestone made of shell fragments naturally cemented together, quarried in Florida — most famously at Anastasia Island, and used to build the Castillo de San Marcos in St. Augustine. It is a natural stone, not a mix.

"Coquina concrete" or "coquina finish" therefore means a concrete made with coquina or shell aggregate. Used carefully it is a useful description. Used loosely it just means "has shell in it".

Washed-shell concrete, or exposed-shell

The plainest and most literal of the four, and the one that describes the technique rather than the look. The surface of a fresh pour is washed or ground back so that the aggregate — here, shell — is exposed rather than buried in cement paste. Any exposed-aggregate concrete works this way; the shell is what makes it a coastal surface rather than a driveway.

This is the term to use if you want a contractor to know exactly what you are asking for.

Shellcrete

A portmanteau — shell plus concrete — that has been in general use in the Florida trade for years. It is a generic industry term, not a brand anybody owns. We should be direct about this because we use the word ourselves and it is on our sign: SRQ Modern filed a federal trademark application for "Shellcrete" in February 2023 (Serial 97794345). That application was never examined and no registration issued. We claim no exclusive right to the word, and other contractors are entitled to use it.

What we do claim is our own mix, our own crews and our own finishing — which is the part that actually differs between two shell decks, and the part nobody can copy by using the same word.

So what should you ask for?

If you want the technique described unambiguously to a contractor, ask for exposed shell aggregate concrete, and say whether you want it as a topping over an existing slab or as a full-depth pour.

Then ask the questions that actually distinguish one job from another:

• What shell are you using, at what size, and where does it come from?
• Is this a topping or a full-depth pour, and how thick?
• How far are you opening the surface up — lightly honed, or ground back to

full exposure?

• What sealer, and on what schedule?

Two contractors using the same word can hand you very different surfaces. The answers to those four questions are what tell them apart.