In which the author tries to make concrete from oyster shells.
I’m beginning my second decade handling shells: I sort them, clean them, coddle them, then take them into the city for harvest. Working in the intertidal zone, my feet are wet nine months out of the year. Oysters have consumed my life and ruined my early retirement. Simultaneously, I have developed a profound respect for the little bivalve. I now believe they are the bedrock of civilization. Indeed they are nature’s masons and have carried mankind on their calcified backs for millennia.
The calcium in seashells has been mined since the dawn of civilization for the binding element in all non-wooden construction. Early American colonists subsisted on oyster meat and built their most lasting structures from tabby, a concrete made from roasted oyster shells.
As anyone who has spent time along the bays and inlets can surmise, primitive man spent many a repast consuming oysters. Archaeologists have been known to search oyster middens to ascertain various facts about our preliterate ancestors.
The next leap, from refuse pile to foundation, is a little more abstract. But as all coastal residents know, high ground is a prized possession. Oyster mounds, after a few generations of accumulation, naturally became the highest ground along any oyster-eating shore. The Doge’s Palace in Venice is built on an oyster mound, as is downtown Boston.
What is more surprising is the link between these mounds of spent shells and the Egyptian pyramids and ancient Roman construction.
Oyster shells are a three-layer ply of calcium carbonate. Known as lime, this compound is the binding element in cement, concrete and some types of bricks. And lime can only be procured from either recently shucked shells or limestone—fossilized shells pressed into rock over timeless eons. Cement is a mixture of lime and clay. Romans perfected concrete, adding aggregate and sand to cement.
The oyster, or any shellfish, extracts lime from the seawater, adds a small dose of protein and extrudes its shell. Then it stacks atop its parents in numberless generations to provide mankind with concrete.
Over the last decade of oyster farming, I’ve killed millions of oysters. I have used their shells for walkways and paths, hoarding them in piles for some later use; I had to take that extra step and—with the help of Google—make tabby concrete.
I have to be honest and record that all three attempts so far have been either partial or total failures. So much for the vast store of data, I needed the tutelage of an illiterate, computerless ancient man.
I thought it would be easy. After all, it only took me a decade to master the art of programming a computer. Within a decade, I had written the one piece of software most widely used worldwide in the securitization of mortgages. Surely, with that kind of alchemy in my background, I could turn humble shells into stone. Hey, the foundation of Trinity Church on Wall Street is made of tabby. It was right up my skill set, I assumed.
But oh no, nature, as I have learned on multiple occasions over the last decade, is much less forgiving and more secretive than any computer. I aspired to mold enough tabby bricks to build a small out-dwelling where I could shelter myself while bagging oysters from the bite of the east wind that hounds me all fall and winter. Sadly, after three failed attempts at conjuring tabby stone from my shell-pile, I confided to my wife I would be happy with just one lousy brick with which I would erect an altar to the Buddha and Baby Jesus.
This summer, I first tried, by massing oyster shells in a galvanized steel bucket and setting that atop a burning pile of driftwood. An hour later, I slaked the shells with water and stirred with my rake. Nothing happened. My worker, an immigrant from Guatemala, noted my defeat and attempted to rescue the moment by pouring a bag of cement into the bucket. “There,” he boasted, “good concrete.”
What he had done was make pseudo-tabby, which is widely used today as a decorative type of concrete, especially around pools and patios. But, it was not true tabby. Later that month, my wife and teenage son returned from Lowe’s with a fire pit: a ring of steel and a mass of concrete bricks that my son fashioned into a circle in less than an hour. He filled it halfway with sand and that night we built a huge, smoky fire to watch the summer moon rise full and beguiling over Shelter Island. Over many loud protests from my son, I covered the bonfire and fire-pit with spent oyster shells, assured that this time, I would convert base shells into blessed concrete. Then a summer storm drove us all indoors; I was certain this was the proper slaking of my tabby. Awaking early, I found my son somberly cleaning out his fire-pit. My shells had done nothing but foul up his sand and cause a dangerous spitting when they burst in the fire.
I checked the Historic Williamsburg website about tabby and the early colonists. They had waited until the dry season, as the roasting shells, when giving up their four atoms of carbon, would search out the humidity and pull the two hydrogens before stabilizing as calcium oxide, the so-called quicklime that I desire. So this very dry November weekend, I invited over friends, roasted a pair of Miloski ducks on the barbecue and fueled up a rick of wood in the fire pit, putting my shells into the galvanized bucket to avoid my son’s opprobrium. We roasted the shells, ate the ducks, drank a pair of North Fork merlots, enjoyed the duck livers simmered in their own duck fat over crisp fall apples, had a delightful squash and pureed oyster soup, drank some dessert rieslings and raked our bonfire well into the night. My wife accused me of early slaking, but the steel bucket was glowing red. My shells had to be ready to turn into mythic mortar.
I stared in dismay at the gray shells that had not turned to stone. Next time, I’ll grind them into a fine powder before I try to roast them. That must be the trick that the ancients have been concealing from me.