What is Shellcrete? Seashell concrete in Florida

Shell concrete, tabby, coquina: one idea, four names

Several Florida contractors use the word “shellcrete,” and the same broad idea also goes by shell concrete, tabby, coquina concrete or washed-shell concrete. Tabby is the historic coastal concrete of shell and lime; coquina is the shell-limestone itself. We are not going to pretend we invented shell in concrete — people have been doing it on this coast for centuries. What we control is how it is placed and finished, and the crews who do it. Tabby, coquina and Shellcrete sets out where each name comes from.

How it is poured and finished

On a resurfacing job the existing slab is cleaned and prepared, the cracks are dealt with, and the new surface is placed as a topping of roughly one and a half to two inches, bonded to the concrete underneath. Everything that decides how it looks and feels happens in the hours after it is placed.

The joints are planned before anything is placed, so the surface cracks where it is told to rather than wherever it likes. On a driveway that can mean timber formwork laid out as a grid across the whole frontage first, so the joint pattern is part of the design; on a deck the lines are cut on a planned spacing, and where a topping goes over an old slab, the old slab’s joints are carried up through the new surface in the same places.

Then the finish. Exposed shell leaves the aggregate standing at the surface, the most textured of the three and the one with the most grip. Honed grinds it back to a soft, flat matte that takes furniture without a rock. Polished goes further, to a sheen best kept under cover. The surface is sealed with a penetrating, matte sealer and resealed as it needs it.

The shell is the material, not a coating. That distinction matters: a spray-on texture sits on top of your slab and wears through, whereas this is a placed topping with the aggregate running through it. Whether your slab can take one is a question for someone standing on it: hairline cracks are ordinary, but a crack with one side higher than the other, or a slab that is moving, has to be dealt with first, because a topping follows whatever is underneath it.

Where it works

Most of it goes on pool decks, often with the patios and walkways run out from them in the same finish. It also goes on driveways, lanais, entry steps and outdoor kitchens, and at a larger scale on resort and commercial decks and walkways.

What it costs

Shellcrete sits at the premium end of decorative concrete, because it is a placed, hand-finished surface rather than a coating and the finishing is skilled labour that cannot be sped up. The number moves with the condition of the existing slab, site access, the finish, and how much prep the deck needs before anything is placed — which is why every job is quoted after a site visit. The one published figure, and what moves a quote from it, is in the pool deck resurfacing cost guide; past that, book a site visit.

Florida code and coastal exposure

Pool decks in Florida have to be non-absorbent with a slip-resistant finish, and sloped away from the water so it drains off rather than back in. Within roughly three thousand feet of saltwater, unsealed concrete also spalls faster as salt reaches the reinforcement. Both facts shape which finish is right for a given deck, and how often it should be resealed.