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.

Scrubble: Carving the Big Tiles

Over the past few days I participated in a wonderful event called StoneFest. The four-day extravaganza brought together stonemasons, sculptors, and letter carvers to share their love for stone. My next few blog posts will focus on what I learned and saw. It was an eye opening experience as I have never worked with stone except to whack off pieces in the field.

Being both a lover of words and rock, my highlight of this year’s StoneFest was the creation of a huge scrabble board, dubbed the Scrubble board by its designer, master letterer Karin Sprague. Each of the 100 tiles was made from a six inch by six inch by two inch block of limestone. The board was a piece of canvas painted to resemble the regular game. It measured about eight feet by eight feet.

Not content with the simple lettering of the normal-sized version, Karin used a 3^rd century Celtic font in what is known as the Uncial style. She then scaled her hand written font up to fit the blocks and traced each letter in red pencil onto the flat face of the tiles. Karin, as well as many of the participants at StoneFest carved each of the tiles. I was surprised how easily we were able to cut the letters.

I don’t mean to belittle what we did; the process went quickly because Karin was a good and patient instructor and because many of those who worked on the letters had extensive experience with stone. We also benefited from the soft, easy-to-cut limestone, as well as the high quality tools we used. It was revelation to me to see how skilled artisans shaped stone, especially the masters who cut with such confidence. You could easily see that every time they hit the chisel with the hammer, the chisel went exactly where it was supposed to go.

After completing our task, we played a round of Scrubble at our celebratory StoneFest feast. About 20 to 25 of us participated. We didn’t keep track of points. We all had fun and I think we all got a good workout hefting the heavy tiles around.

1880 Census Repaired

Earlier this year, on March 6 to be precise, I described a wonderful book that I had been given by my nephew. The book was part of the Census of 1880 and contained a lengthy section devoted to building stones of the United States. The book is still very cool but now it is even better.

What I hadn’t noted before was that the book was in terrible shape. The cover was more wolf-eared than dog-eared it had been so severely damaged, and the main part of the book was barely attached to the spine. Every time I opened it, I thought it was going to fall apart in my hands. In addition, the one large map in the book was ripped almost into two pieces.

So being the diligent book owner and book lover, I decided to get my new, old book fixed and gave it to book conservator, Carolina Veenstra. Four months later the book has returned. The book looks great. It has a new cover, the spine and the pages are attached to each other, and the map has new backing. I can read the book without fear of ending up with two books in my hands. I can linger over the color plates, many of which have a sheet of thin paper protecting the images. I can unfold the map.

In this day of Kindles, ebooks, and Google books, it is even more of a pleasure to own this handsome tome. It pleases me to no end, knowing that I have preserved a 129-year old book, a book that someone will still be able to read in another 129 years, no matter what new technology we develop. That is one of the simple pleasures of these items we call books. Plus this one has that amazing old book aroma, one of the world’s great smells.

As I turn the pages, I like to imagine the previous owners. Were they quarry owners? Were they seeking out rocks for a project? Were they other nutty geogeeks simply interested in the stories that stone tells? I am sure they were all of that and more. I am also sure that this book will provide me with many more years of enjoyment.

Fire and Stone

The recent and tragic fires around Los Angeles have prompted me to write about the connection between fire and stone. Vitruvius was one of the first to consider the connection. In his landmark De Architectura, or The Ten Books of Architecture, written sometime between 31 and 27 BCE, he wrote of travertine blocks. “They cannot be safeguarded against fire. As soon as they make contact with it, they crack apart and fall to pieces.” Instead he recommended the use of tuff.

Like the Greek philosophers Aristotle and Plato, Vitruvius considered that matter consisted of unique combinations of the elements water, earth, air, and fire, which gave an object, such as a stone, unique properties. Too much air and fire, according to Vitruvius, made travertine susceptible to breaking at high temperatures. Modern scientists point to the unequal amounts of extension and contraction along internal crystallographic axes in calcite for travertine’s poor performance in fires. Geologist Marie Jackson has found that tuff survives fire better than travertine because of its porous texture, which allows tuff to expand when heated with far less fracturing than travertine.

The problems caused by fire often drove building practices. In 1680, the General Court in Boston passed a resolution requiring slate roofs, after a fire destroyed 80 buildings and 70 warehouses. Others fire led to cities such as Boston, Seattle, and New York passing laws stipulating that new buildings be built with stone or brick. And James Flood’s brownstone mansion was the only building on Nob Hill to survive the fires that followed the 1907 San Francisco earthquake.

Former James Flood mansion, Nob Hill, San Francisco

The argument has also been made that Chicago’s Great Fire of 1871 helped make the Salem Limestone the most commonly used building stone in the country. Historians and promoters of Salem Limestone have written that the “buildings that suffered least from the fire were of limestone.” Newspaper accounts from the time, however, report that during the fire, limestone “seemed as though [it] actually burned like wood.” Builders were so prejudiced against the local stone, most of which came from nearby Joliet and Lemont, that in the first 30 days after the fire, most ordered brick, from as far away as Philadelphia.

Chicago Auditorium by Sullivan and Adler (copyright from Boston College professor Jeffery Howe)

The true qualities of the Salem—durability, accessibility, and ease of cutting—ultimately proved superior. By the mid 1880s, architects such as the high-profile firm of Sullivan and Adler had begun to use Salem regularly, most prominently on their Chicago Auditorium, built in 1887. Others followed, demand grew, limestone-laden trains bore north, and Salem buildings spread across the Windy City. By the mid-1890s, the Salem limestone was being shipped across the country, en route to staking its “most popular” claim.

The Getty Center (copyright David Williams)

Two months ago, another fire in Los Angeles made it into the news. This one threatened the Getty Museum. If the fire had engulfed the buildings, they would have put Vitruvius to the test. Travertine, and in fact, travertine from the same quarries that supplied Rome in Vitruvius’ time, clads the Getty’s buildings. Fortunately, fire fighters contained the blaze and no stone was harmed. I also suspect that fire fighting has improved a bit in 2,000 years.