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Lime Kiln Report, May 28/01

by Dave Nielsen <>

(Dave is a first year student in the Heritage Masonry Program at Algonquin College in Perth, Ontario. As a class project, they built a 3 ft diameter beehive shaped lime kiln)

The Lime kiln project began from an idea passed on through the school to our Director Nelson Rogers. Under the direction of Mason and teacher John McDougall; seven students began the process of designing and constructing a conical beehive shaped kiln roughly 8' tall and with an exterior circumference of 4 feet and interior firing chamber of roughly 3 feet.

With research and help from Norbert Senf we came up with a fairly simple design and began the construction for our mobile kiln.
We started in January, and were lucky enough to have space within the school shop so we did not have to set up any heating or outdoor workspace. We started by pouring a concrete pad we could have machinery hook onto and drag the kiln when it was completed to the outside. The kiln slowly but surely rose from the pad with roughly six guaranteed hours a week and anywhere from 2 to 5 students working.

We had cast iron doors donated by a local welder, which were both installed on one face, smaller one as the wood door and the larger for the stone chamber.(We found we needed to leave more room for expansion at the door connections as most of the cracking that occurred radiated from the corners of the doors.)

It took us roughly three months to build while trying to incorporate school and all the other projects and good stuff called life. But just before all the snow melted we finished and had a back hoe make a snow road to pull the kiln to its burn spot. That day we fired her up and reached 800 degrees.

  The second stage was the burns, at which point this article was started. The burns were quite long and required a lot of attention. We burned strictly with white ash although in future we would like to research more about the variety of woods in our area and their affect on costs and putty quality. Each sample of lime stone, which were gathered from six separate locations, were 500 pounds. We found on a rough average that we lost about 150 pounds in the samples mass through the water evaporation and pieces falling into the fire chamber. The good thing was and we don't have exact numbers yet but the expansion rate gained in mass from the quicklime reacting with water into putty form seemed to increase quite a bit.. Each sample had its own reacting time, heat rate, colour, and texture. One of the only common qualities were that they all were an 11 on the Ph scale which is well known to be a high alkaline.

For slaking the samples we were not entirely organized and finding containers and storage was not as complete as should have been, but all the samples were done and placed in large olive containers to rest the summer and mature. We slaked in mortar pans and then screened the putty as it was placed in the storage containers.

Right now we have done our final report and are waiting for the composition tests we were able to have Parks Canada do in their labs.
We are hoping to have this project stay as a long term research opportunity within the school for students to become aware of the importance and use of slaked lime when dealing with heritage or restoration projects.

In the future, we would like to research different kiln designs, grate material (we used cold rolled steel grates and they lasted roughly two burns each; we went through four of them and needless to say we would like to obtain a much more substantial grate.), Quantities and qualities of various woods, the affect of ash in putties, kiln materials, Temperature and time ratios and obviously the structural, practical and applied use of lime putty mortars.

This project is relatively open in that we would love to hear of any interesting ideas to research or try out, questions and inquiries, visits and possibly workshops. I personally, and everyone involved believe that this is an exciting and viable opportunity for the future and hopefully our research will help recover some lost techniques within our fine trade and provide for more accurate and beneficial heritage practices.

March 25/01 report

Kiln update: We have completed two burns, the first burn the temperature got to 1500 deg. F and the second one was up to 1750 degrees.

The first batch of stone ended up being a mixture and did not end up consistent but all pretty much slakeable and I haven't seen the second batch yet. The kiln is holding up, cracking has been fairly surface and mainly I believe due to lack of space and insulation in the front face around the doors. Most of the cracks are radiating from the corners of the doors. The ceramic blanket has been a savior for our doors which turn cherry red without the protection. When the kiln cools the cracks all go to their original positions which we took as a good sign.

We also used a vaccumm cleaner to blow air and improve heat up time and so far a success. Our grate was white and I'm really surprised it lasted the second burn it was falling apart and sagging over an inch. It lost nearly half its thickness and bowed during the first burn so we took it out to flip it over for the second but I think we got lucky. We have another grate cut for the next burn. Tomorrow we are going to check the insides and see what damage has been done and hopefully do some maintenance. I'm hopeful it will last the six burns.

So far we have done eighteen hour burns. Unfortunately, I got the late shift both burns. I was stoking the fire at five in the morning Sunday morning the flames are a deep deep red and fly out the top sometimes three feet, that's why we decided to have someone watch at all times. Inside the fire box last night the embers were a glowing white and all the surface flames were a distinct violet purple, one of the more beautiful things I have ever seen.

We have four more burns to go through so I'm sure lots will be learned in the next week. We also have to come up with a proposal for a new project next year. One like this year's, but with observed improvements and another system where the fire box is outside the kiln and a draft draws the heat into the cooking chamber. We would like to try terracotta or something like specialty bricks such as glazed types. It depends a lot on the interest we'll get to help work but the interest is rising since the firing started.

Update: April 6/01:

We are on our last burn! All our samples so far have been slaked ( Some slower than others) but all eventually became very nice puddy. We have large sealable containers to keep the large part of the samples for the summer.

The temperature reached over two thousand degrees, some sandstone "accidents" were glazed and glassed over with a variety of colours.

The kiln has held up and no more severe cracking. With the doors well insulated the cracks made previously do not open.

I want to send you some photos of the project to put on the web site. We have quite a few although I haven't seen them.

Update: April 11/01


Laying out the base course of firebricks. Kiln is on a concrete skid so that it can be moved outdoors.
This is Algonquin College's masonry shop. Note the limestone carving projects in behind.
John McDougall is to the left.

Top of firing chamber.

Forming the exit of the main chamber.

Reinforcing strapping in place. Brick facing started. Note insulation behind facing.

Completed kiln being skidded outdoors with a backhoe. Bottom door is for firing.
Top door is for limestone.

This page last updated on May 28, 2001

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