Month: September 2009

StoneFest: Making Mortar

Several times during the research for my book on building stone, I came across references to making or using mortar. In particular, in my chapter on coquina, I described how the Spanish burned oyster shells to make lime for mortar. I sort of understood the basic process, but again, not until StoneFest, did I get the process of what the Spanish did. One of the first projects at StoneFest this year was to make lime for mortar.

Irish stonemason Patrick McAfee was our teacher. Patrick is the author of two excellent books on masonry, Irish Stone Walls and Stone Building, with over 40 years experience. He lives and works in Ireland, an ideal place to practice his stone masonry. As he said “The land was so poor all you could grow was stone.” And they ended up in the 4,000 castles, 25,000 bridges, and 250,000 miles of stone walls found on the Emerald Isle.

As with letter carving and making windows, the process of making lime was easy in the hands of a master. We began by building the kiln, basically a tower of stacked cement blocks. We enhanced it by cutting holes in the corners, to allow air in, laying a metal screen on the first row of blocks, and by holding it together with steel beams and tape. The gang took about 40 minutes to build the kiln.

Building the kiln.

Raw Texas limestone before being put in the kiln.

We put coal and limestone on the screen and continued to add these two ingredients in about equal parts as the kiln grew. And this was all we needed to make lime. We could also have used wood or peat for fuel and shells or marble for our lime source. Our limestone came from Texas but historically builders would have used the local materials, as the Spanish did when they burned shells collected from middens made by people who had lived in the area more than 5,000 years ago.

Raw coal before putting it in the kiln.

Feeding the kiln with wood. Note the holes in the corners for air intake.

When we opened the kiln the next day, the limestone had been converted to quicklime, white lumps of CaO. The heat had driven off the CO2, changing the calcite (CaCO3) to quicklime, a highly reactive material when mixed with water, a process known as slaking. The reaction produces lime putty, calcium hydroxide (Ca(OH)2). Lime putty can be used by itself or mixed with an aggregate to make mortar. Patrick told us that lime putty gets better with age, as not all of the quick lime hydrates. The Romans waited at least three years to use theirs and Patrick knew of Polish lime putty aged for more than 100 years.

A bucket of quick lime: these pieces resulted from driving the carbon dioxide off of the calcite.

Our final product: slaked lime or lime putty.

In a little over 24 hours we had made one of the key ingredients of construction used for more than two thousand years. Yes, we had cheated a bit some using modern items but this was because we were in a class with a goal of learning how to make the lime. But basically we had performed a task that would not have looked too strange to Roman builders. Patrick said “We are in a parallel universe for the next four days.” He was right. Our universe was one that relied on simple tools, basic, but highly honed skills, local materials, and practical know how to generate beautiful and lasting products. I hope I get to return to StoneFest next year to continue my stone education in this parallel universe.

StoneFest: The Stone Masters

As someone seriously interested in rocks for the past 25 years or so and building stone for the past dozen, I am embarrassingly bereft in my practical knowledge of pounding rock. Yes, I have whacked rock on many an outcrop (and, of course, played numerous rounds of rock hammer golf), but never had I hammered rock with the goal of creating a shape, such as a letter or block, or even watched someone else hammer rock, until StoneFest. As I stated in my previous post, it was a revelation.

Stone and hammer: some of life’s simpler pleasures.

The master stonemasons were a joy to watch. Each time their hammer or mallet struck the chisel, it was done with confidence. The confidence manifest itself in three ways. First, was in having the right tool. Second, was in locating the chisel at the right point to take off the precise piece they needed, and third, was to hit with the right amount of pressure. They were the masters of the rock. But they also knew that stone could be capricious and they did make errors.

Keith Phillips showing the various textures one could apply to stone with a hammer and chisel.

I especially enjoyed watching Keith Phillips, who is the master stone cutter at the Tenino Sandstone quarry, 20 miles or so south of Olympia, Washington; and Nathan Blackwell, 87 years old and still making his own tools and cutting stone. They helped one of the students cut an S-shaped curve called an ogee. Nathan was particularly impressive, getting into a hitting rhythm as he trimmed along the curve, took off surface rock, and began to cut out the shape. It was if the tools were extensions of his hands. Within minutes the block had metamorphosed from a rock to an arch.

Nathan Blackwell at work. An exemplary gentleman who always wears a tie when cutting stone.

Robinson Jeffers once compared stone cutters to poets. Each works precisely, deliberately, and considerably to fashion their particular work of art. He wrote in his poem To the Stone-Cutters:

“Yet stones have stood for a thousand years, and pained thoughts
found
The honey of peace in old poems.”

The final product: an ogee arch cut with a hammer and chisel, the marks of which give the arch its texture.

Keith Phillips said “Oh, some people say, it’s just stone but we are trained to be accurate, to build a building that will last 100 years.” Keith’s comments gets to the heart of the passion I felt at StoneFest. These were people dedicated to making high quality and often beautiful products that would endure. In our modern age of prefabrication and machine made items often put together half way around the world, it was a treat to watch these people work with tools that had basically remained unchanged for centuries. I know that I forget the amazing items that talented people can produce. It was both a revelation and a reaffirmation of the human spirit.