Lime Burn

Though it's been two weeks, we wanted to provide some more information about the recent lime burn at the Colonial Williamsburg Brickyard. Joshua Graml, an apprentice with Historic Masonry Trades, volunteered to explain the process:

The Colonial Williamsburg Brickyard successfully built and burned a lime rick recently. Lime was an important product in the 18th century building trades, being the key ingredient in both mortar and plaster. The week of February 9-13 was spent constructing the rick, which consisted of a wide circular platform of firewood about four feet tall, topped with a large mound of oyster shells. On Saturday, 14 February, the central chimney was lit and acted like a fuse to ignite the firewood, and over the course of the day, burned the oyster shells. The wood burned down, and on the morning of Sunday, 15 February, the Brickyard staff was left with a large, still-warm pile of burned shell. Chemically, burned oyster shells are quick lime. Sunday found us "slaking" the lime by shoveling the burned shells into tubs and gently pouring warm water over them. An exothermic reaction takes place, breaking the burned shells down into what the 18th century lime burner would have termed "slaked lime": a white, caustic substance that looks and feels kind of like ricotta cheese.

The slaked lime was separated from the ash and the non-reactive leftovers of the burned shell on a large mesh screen, and stored in a pit in the ground. These lime pits filled rapidly over the course of the following days. Any impurities in the lime will sink to the bottom of the pit, leaving us with good, usable lime for plastering the Charleton Coffeehouse this summer. In the pits, the lime is covered with water, which will keep the lime from absorbing carbon dioxide and hardening. Differing amounts of sand are added to lime to make mortar for laying bricks, or in this case, for plaster to plaster interior walls.

Lime ricks are burned every couple of years by Brickyard staff, on an as-needed basis. The design of this rick was different from ones burned in the past; it is based on Jamaican style oyster ricks. Colonial Williamsburg architectural conservator Matt Webster suggested the design, and helped the Brickyard staff construct it. By the way, the term "rick" is an old English word meaning a stack, usually referring to hay or cord wood.

We'd like to thank Joshua Graml for sharing information on the burn. For anyone who might be intersted, here is a brief summary of the chemical processes involved:

Common Name Chemical Formula
Calcium Carbonate
(often seashells or limestone)
is heated to approximately 750-900° C
releasing Carbon Dioxide - CO2
and leaving Lime
(Calcium Oxide)
= CaO
adding Water + H2O
creates Slaked Lime
(Calcium Hydroxide)
= Ca(OH)2 + significant heat energy
exposing it to Carbon Dioxide + CO2
releases Water - H20
leaving Calcium Carbonate once again
(in this case, dried mortar/plaster)
= CaCO3

Chemical Elements: Ca - Calcium, C - Carbon, H - Hydrogen, O - Oxygen

Photos by Jessica Krop and Peter Inker

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Rick Brouse's Gravatar

Hmmmmm.....There is a Town in Pa. callled "Limerick, Pa." Wikapedia tells me that it was named after a fella who came from "Limerick, Ireland". there a connection to "Lime-rick, Ireland" and what they may have been done there? Were they burning oysters shells in a "LIME RICK" perhaps?!
OK,"Limerick Ireland" next google!

Posted By Rick Brouse | 3/4/09 2:52 PM
CWFan's Gravatar

Many thanks for posting the chemical process! How far back does slaking lime go? I think I remember one of the interpreters mentioning that Greeks or Romans were very familiar with making mortar and plaster, so much so they knew how to create a mortar that would set underwater! The depth of knowledge tradespeople like Josh and Jason have in their field is astounding.

Posted By CWFan | 3/4/09 11:14 PM
Joshua Muse's Gravatar

While this USGS article focuses on contemporary statistics, it opens with a short paragraph on the history of lime use. The author points out that lime was used by Greek, Roman, Chinese, Egyptian, and Tibetan civilizations, and that it may have been used as early as eight to fourteen thousand years ago.

Posted By Joshua Muse | 3/5/09 11:24 AM
John Peebles's Gravatar

It would be interesting to see the process of creating "tabby" detailed as well as this lime burning was. Thank you.

Posted By John Peebles | 8/6/10 7:53 PM
Joshua Muse's Gravatar

For those who aren't familiar with Tabby (I admit I fall into that group), here's a link with a bit of information:

Posted By Joshua Muse | 8/11/10 10:43 AM