Lime kiln

Left image
An artist's rendering of lime kiln with smoke.

Right image
Tumacácori's lime kiln

 

• Fire Crackling

  
  

  Lime kilns had to be kept extremely hot for days at a time in order to complete the chemical reaction that turns limestone to quicklime.

  Date created:

  10/14/2020

  Audio Transcript

  fire crackling

 

How It Was

Although the word "adobe" brings to mind "mud," Tumacácori's earthen architecture also relies on limestone. This rock, whose geologic origin stems from an ancient seabed, is used to create plaster, mortar, and whitewash that protects and smooths the finish on adobe walls.

Tp make lime plaster and mortar, imestone had to be transported from the Santa Rita mountains by oxcart. It would then be placed in the lime kiln on a metal grate. A fire was lit under the boulders and burned at high temperatures until the boulders began to swell and break open. At that point they could be hammered into a powder which was then “slaked” by putting it in water for a day or two. Once hydrated, it was turned into a paste, sand was added to make plaster, and it was spread onto adobe walls to dry.

Lime plaster was used on both the exterior and interior walls of buildings. The thickness of the plaster coating was 1/2 inch to 2 inches thick. The walls of the mission church were painted with a double coat of plaster.

Many people in the Tumacácori community spent many hours working at the lime kiln, transporting boulders, pulverizing cooked rock, and mixing lime plaster for all of the walls of this large mission community.

 

How It Is Now

With the invention of cement, concrete, and plastic, lime is no longer the industry powerhouse it was in the 18th and 19th centuries. Lime kilns have become historic structures themselves.

However, limestone plaster remains the single best protector of earthen architecture. Unlike cement or many other plastic or sylicone-based products, lime plaster protects the adobe walls from moisture, while still allowing them to breath and wick out moisture that may travel in the walls from ground water or rain. The walls at Tumacácori are protected with a coat of lime plaster made with the same proportions of dry lime, water, and sand as the original coating – one part slaked lime with four parts of sand.

Lime plaster is effective, but requires frequent maintenance. Even the lime kiln itself is preserved with lime plaster to keep moisture from deteriorating the ruins further.

 

Learn More

Tumacácori Preservation
Tumacácori Preservation Techniques
Technical Preservation Services - Adobe Buildings