Quick overviewOne of the goals was to provide an understanding of lime's role in building construction applications. Applications discussed included contemporary and historic mortar, plaster, stucco, restoration and limewashing, and many of the lime standards that are used around the world. It was also a goal to show the need for all groups to consider more effective ways of communicating and sharing the knowledge about this wonderful material. Many skills have been lost and forgotten over time, so relearning and revitalizing interest in techniques was a high priority and mentioned often.
The program included 38 presentations that approached the topic from every angle. I must say that the speakers made the programs lively, interesting and worthwhile. Another highlight was the series of three workshops that demonstrated lime-based mortars, fresco painting and limewashing. A diverse group of 120 people were in attendance including university faculty, lime producers, building conservation specialists, architects and many tradespeople from 17 different countries. This was of course the first event of its kind and it was really a rare opportunity to have so many experts on hand speaking on this one topic: limestone.
Workshop #1: Lime Based MortarsJohn Speweik, of U.S. Heritage Group Inc., spoke and performed demonstrations on the topic, "Restoration of Pre-1871 lime-based mortars." Speweik speaks to the audience and shows the characteristics of quick lime. He's showing here how limestone was super heated, turning it into quick lime and the effects when water was added to the rock. In times past, a hole 4 feet by 5 feet, 6 feet deep was dug out and the quick lime was added to water. This mixture was allowed to sit and absorb water for several months or even up to a year. This type of putty did not present problems in times past for ancient groups because they would age it for more than three years so it did not pit and stuck well to the wall. Traditionally, the pit of lime was divided up between trades: The top of the putty (1 to 2 feet thick) was for plasterers and for those doing fine fresco work. The bricklayers would then have the next layer. Speweik then showed how to mix the ratios of sand to lime to make sure a quality mixture was obtained.
TuckpointingOne thing that Speweik emphasized was the fact that keeping water from getting into a building is not possible and should not be the main focus. Releasing water from a building is the key issue. Problems occur when water gets trapped behind hard cement mortars in the joints and doesn't allow moisture to escape. This was not the case in pre-1871 mortars and this brought up an interesting point.
He mentioned that mortars at that time were made from lime and sand. Though we might think of this as weaker than the modern-day Portland cement-based mortars, it actually proved superior.
"When water gets into a building, it eventually comes out," he says. "Lime- and sand-based mortars allow this to happen. And in the winter, when freezing occurs and causes the stone or bricks to expand, the mortar is weaker and takes the pressure, causing it to crumble and take the pressure away from the stone or brick face. This is actually one of the goals of the lime mortar-to fail before the stone or brick fails. Over time, tuckpointing is done and replenishes the joints again."
He then addressed two of the big problems that occur frequently on restoration projects. One is the use of Portland cement and how it's often used for tuck pointing on historic buildings in an attempt to restore them. The concept is, "stronger is better." However, this is causing major problems.
The buildings absorb moisture through the stone or brick. The joint now is stronger than the surrounding brick or stone, being waterproof in effect. Expansion in the winter from freezing of this moisture puts increased pressure on the stone or brick, with the resulting popping of the brick face or cracking of the stone. Another problem is the way joints are opened up and cleaned out. Too often, the stone or brick are damaged by careless use of grinding and chiseling tools. Instead of restoring, they actually end up destroying the work. Speweik's knowledge of this subject was truly appreciated by all and will be put to good use here in the U.S. and abroad.
Workshop #2: Fresco PaintingThis very enjoyable workshop was put on by Tessa Lindsey, who has studied this fine art in Italy. When one thinks of Fresco, probably the most familiar person and place that come to mind are Michelangelo and the Sistine Chapel. Fresco is the art of painting on fresh lime. The color (the pigment) contains no glues or adhesives and is bound to the surface by the carbonization of the lime itself. The layers of plaster are built up over a surface until the final layer (called the Intonaco, which is about 1/8 inch thick) of fresh lime and sand are applied. The painter then has about six to eight hours to complete the painting over the plaster. This is how Michelangelo did his work-he would plaster the area in the morning, then paint that section, adding on to it the next day, eventually covering the entire ceiling!
This workshop proved how much of an art plastering really is, and I think it inspired many people to consider trying their hand at this medium that has been around for hundreds of years!
Workshop #3: LimewashingI must say that Pete Mold put on one of the most interesting workshops I have ever attended. Photo 6 shows him in action as he shares his wealth of knowledge on this topic. Mold pulled out all the stops. With much effort, he brought in these huge concrete slabs to demonstrate the fine art of limewashing. He showed us what limewash is made of, and how it's used to protect and make buildings more durable. He showed how it's applied in thin layers, with the brush marks disappearing after the second layer is put on. With a few layers, it's still quite absorbent but as the layers build up, water actually rolls off of it rather than going straight in. Mold has done limewashing in pretty much every country you can imagine, and the advantages of this type of coating on a building were readily seen by all who were in attendance.
Judging by the success of this first years event, I'm sure some of the speakers and presenters will be back again next year, along with a new series of programs sure to enlighten and delight all who are fortunate enough to attend. Perhaps the next time this symposium comes around in 2006, you will be able to be in attendance. From my perspective, it will be well worth your effort to be there!