This lecture is part of the 2009 Nationwide Cemetery Preservation Summit
Performance-based Evaluation of Materials & Methods for Monument Conservation by Norman R. Weiss and Irving Salvid
Norman: You’ve heard the title of the lecture, let me give you an idea of what it’s going to be about using this opening slide. This is a place that even most Londoners have never seen. It’s a building in London that amazingly enough survives to the present time. Built in 1874, it is as far as we know, the oldest testing laboratory in the world. Doing things the way we do things today. In the history of engineering, there are very few things as important as this building. It is the Curcoli Experimental and Testing Works. It still has in the building a machine that was so big when it was constructed that it’s too big to take out of the building. It is a 48 foot long screw press for testing full building assemblies with loads up to 300 tons. 1874. Relatively few laboratories had that in the 1974. It’s an important place. What is really exciting here, and I hope you will agree, is that this is what’s over the entrance of the building. In a way, this has guided not only the development of today’s electric but has guided of lot of things that Irving and I have done at MCC Materials for the last 14 years now since we established that firm.
My computer’s not behaving itself at all for some strange reason. So again be patient. Let’s talk about this for a moment. What we like to present to you here is a range of ways in which we prove, disprove, in some cases even try to predict the issues that are really important to us in historic cemeteries. And as you’ll see I think through the presentation, sometimes our questions are really what are the important issues? What is it that we’re trying to look at? What is it that we are trying to understand through testing? The important thing at least at the outset here is for you to recognize that what we are saying is that there is a range of testing options and a range of testing procedures.
From some things like this scanning electron microscopy. We’ve just seen a presentation that had a partial reliance on scanning electron microscopy, at the sophisticated end to some very, very simple low tech things. There is, just as scientists have said, there is no one particular treatment to deal with the issues of stone conservation, there is really not one particular assessment method, analytic method, testing method, imaging method, that really makes sense for all the kinds of problems that we deal with. But on the high tech end, we have things like this, that’s Jamie Martin at SEM in the lower right, here actually is an image of a partial treatment with ACT, as you just heard, on a calcite cleavage . This is what it actually looks like under a microscope.
Sometimes you need to take instrumentation into the field. That’s easy if the instrumentation is small and portable. It gets more and more complicated as the instrumentation is more sophisticated. Yes, that’s me right on the left. Yes, surprisingly enough that’s Jason on the right without hair, without that much hair at all. But the issue of portability. When we get to that idea that we want to perform some tests incito on our monuments. I will kind of bounce back and forth between monuments and buildings in the presentation, but when we want to do both laboratory and field studies to determine or predict effectiveness, which is what this really about, then we need to have instruments that are affordable. Sometimes affordable instruments are packaged in ways that make them look relatively small, but they are, trust me, surprisingly expensive.
There are other approaches. Among those other approaches are the relatively inexpensive, affordable instruments each of which has its limitations but each of which does a service for us. Now we are much over in the realm of buildings and engineers structures, and as you’ll see I think through the presentation, there’s a lot of back and forth between these two realms. Cemeteries on one side and buildings on the other. On the left is what’s called the Schmidt Pendulum Hammer, it’s used in the concrete industry. We’ve made a lot use out of it for stone testing as well. It’s a very interesting, relatively easy to use device for determining strength, at least surface strength, indirectly in the field. Some of you might recognize on the right hand side, a relent tube, which is used in water absorption studies in the field directly on the building or monument.
Here, oddly enough, as we get lower and lower and lower in the technology, we become more and more relevant as we’re able to actually study the things that we have treated or are considering treating. At the far low end of the technology, we actually find that we’re spending a great deal of our time trying to develop and improve method like this. What you’re looking at here is a very fragile French limestone that is used throughout France and Belgium and the Netherlands, and the test here is the tape adhesion test. And yes these tests are incorporated into some of the ASCM standard tests that are part of the engineering world. Tape is applied, pulled off, I call it the Brazilian bikini wax test for stone consolidation because you kind of jerk that thing along and hope that the stone doesn’t experience too much distress.
The two tapes that you’re seeing here, the one at the top was done before any kind of treatment. The one below it, in a nearby area, you can’t take it on the same place obviously twice, but a nearby area after treatment. It’s a relatively simple assessment of the cohesion of grains on the surface. Surprisingly enough, no matter how much money you are willing to spend, there really is no instrument out there that can do it as well as this test which takes I supposed roughly 3 cents worth of painters blue tape or electrical tape or some other standardized tape material to actually perform it. We’ve performed over the large areas, can be performed easily and very quickly on large numbers of monuments. We are getting more and more interested in the low tech end of assessment.
That brings me to the kind of core concept. I supposed the core concepts of what we do should be obvious, but since not all of you are involved in the technology end of conservation, let me just quickly zip through the basics, the conservation 101 basics of what we do. This is actually some hands-on inspection of the Omaha, Nebraska workshop that NCPTT did in 2005 as part of the whole workshop series. The basics are essentially this. Determining through the hands-on inspection, out in the field, real world circumstance, determining what the composition and condition the monument really is. That’s the first step.
Second step, establishing conservation needs and what the priorities are. Sometimes those needs are pretty drastic. This is a follow-up photograph after the tornado that hit the Great Barrington Cemetery in 1995. This is actually a little bit later on, but the destruction to trees and then in turn to the monuments that were hit by large limbs and toppling trees, plus those monuments that were literally sucked up in the air and then tossed, sometimes long distances as a result of this tornado, pretty staggered. So to go through here and establish needs and prioritize the needs is a difficult process, perhaps more difficult than some of the sites that you have. Then finally of this basic package, identifying a range of what I would call potentially useful treatments. Things that you believe from what you know and what you can read in the literature have some potential to be really handy.
The question then is, well how do we narrow down that range? How do we close in on specific materials and methods? How does the conservator do that? The answer is that there is once again, a kind of litany, a simple litany of what conservators do in making those choices and our point in the presentation here is that we think we can make that better. One of the things that we talk about all of the time is ease of use. The ease of use is an important issue. Sometimes that’s really literally just suitability to the conditions that you have on site at the cemetery. You’re going to see much more about this. This is our field laboratory at a site, I won’t tell you any more about it, you’re going to hear from Irving and from Martin Johnson about it tomorrow morning. I will just say 2 words of explanation: Survivor Samoa.
The question here is do you have treatment techniques that seem to suite the on-sight conditions, which are never the same conditions as the conservator doing treatment in the workshop/laboratory circumstance. Finally, there’s an issue of personal experience with the products and a kind of level of comfort of working with the products. The comfort can include self and hate, that’s interesting, self and hathy issues. That’s health and safety issues. Apparently inverted.
What else goes into this blend to determine whether a particular product is chosen? Well, manufacturers’ recommendations and sometimes information that manufacturers give us, which includes legal issues of whether the product is available to be sold in a certain part of the country, which typically these days in the United States means compliance with VOC regulations. So here’s the VOC map, and as you see, most of the country is not regulated. But then where are the historic buildings, and historic cemeteries that most of us work on, an awful lot of it is in those darker colored states plus the state of California. No problem, your grey ones from Oklahoma or North Dakota, but we have a lot more monuments and cemeteries in other areas, so VOC issues are starting to become extremely important and they become part of the decision making process along with other obvious things like product costs. Many of us instinctively do not want to use very expensive products. We just feel somehow that that’s a bit odd. We’ll come back to that.
Now, we put all of this together, we make the materials, methods and decision and then how do we judge our success? What I’m talking about is effectiveness, we judge our success some times in the wrong ways. One of the ways that we judge them is the appearance upon completion of the work. Well, there are a couple of areas in which that might be significant. Sometimes when we do replica mortars for patching of stone, we know an awful lot about success and failure on a visual way based on what we see. What we see in the lab, what we see in the field after finishing the surface. Sometimes that’s reasonable. We haven’t made major mistakes at least, but what we’re trying to do here … this is a circumstance that many of you have been involved with and still might see. Trying to do aggregate matching to minimize the discrepancy between the short-term appearance and the long-term appearance. That’s great but that’s still appearance upon completion and it doesn’t really address this bigger issue of effectiveness.
Sometimes there’s the question of short-term behavior without obvious failures. Just after a relatively short period of time, it seems to work. Here’s a project that we worked on a number of years ago with Ava heritage this is Winchester Palace in London in Suffeck. I’m not too happy, I was about to walk away from this one. It turns out it actually did work reasonably well but you’re out there, you’re trying to judge just a few days later what’s going on. If you’re lucky, sometimes you have a chance to do mock-ups like this and even review them after a few days, after a few weeks, sometimes even after a few months.
Now here’s one step further, being able to go back after a year and take a look at your work. That is the condition before. This is a sort of aggregate filled surface there to do this repair, to make it look right. A year later it still seems to be looking pretty good. That’s the kind of thing that really matures the process. To be able to go back not just a week later, but a year later and say, “Well I think we’re still doing really, really well and the aggregates we have are are co-stable materials.” They still look good examined with a hand lens. The materials that we used we can look at again in the laboratory, but here’s a year of field exposure. So that’s the idea of reviewing full-scale work. To be able to say, “I’m still comfortable.”
There are some dilemmas here that we need to get through quickly. One of them is the basic dilemma of testing. Laboratory testing first and then we’ll talk about field work. The basic dilemma for me as a scientist is that I have to remember that the standardized test methods that architects and engineers specify, these things are mostly about quality control and not so much about performance, and we need to remember that. Some of them are really problematic because they demand very large samples. Here is a flexible strength test used in the marble industry. If you were selecting new marble or if you were trying to see if your marble monument was as still strong as it should be based on some ASTM standard which is C503, you go ahead and perform the C880 test except what do you need? That piece of stone that has just been broken in our machine is 15 inches in length. You need to break at least 3 of them and if the marble has any significant figure, you need to break 3 more with a figure oriented 90 degrees to it. Where are you going to get 6 15 inch pallets of stone out of that wonderful headstone that you are just about to conserve.
These tests don’t really work for us because of size of specimen and the number of specimens doesn’t make sense. So we turn away from that at times and we say, “Let’s get new stone. Let’s test our stone treatments on new stone.” The particular project here, what did we do? We went to the [inaudible 00:13:36] mine, which is really a mine rather than a quarry, we said, “Let’s match the appearance of the grades of [inaudible 00:13:43] that are sold today with the stuff that we actually had in the field on this building. We got samples of those, we ran the tests, but then, it’s fresh material. That is the ultimate dilema. You’re testing fresh material, trying to see if it can be upgraded with a conservation treatment it generally can’t. You can’t improve something that is currently at the top of its form. If you are going to see differences, they are very, very small subtle differences. They may not make a lot of sense but they don’t present the condition that you are trying to study.
As we saw a moment ago, sometimes better samples are real world samples. Here’s pics a gravestone. This makes perfect sense. You see 2 weathering zones there, that’s a real thing. Or we can go to buildings where we can get large samples of weathered material but the problem is, although there are scores of larger specimens, they are so heterogeneous in their condition that they don’t really work for testing. Because instead of just testing Product A versus Product B, you may be testing the outside, the inside and so on as you begin to cut up the samples. So instead of a testing program with a single variable which is telling which is better A or B, you now have at least 2 variables, maybe even 3 variables as a function of some other aspect. This whole approach again is flawed in one way or another.
We found that we have to turn to smaller and smaller samples because they can generate significant number of them and because we can accept or reject them based on the appearance of the sample. It seems to be without flaws, it seems to be without a crust or a soiling area, or a stain, and so these are, it’s hard to tell without a scale, but these cores for example over here are about this big. They’re 14 mm cores, so they’re about the size of my pinkie. The cubes are 1”, so 2.5 cm cubes. The discs are really quite thin, I think they are about 8 or 9 mm in thickness and so on. The slices up top, even thinner. Quite fantastic. We’ve turned in that direction and I want to show you just a few examples of what these things are all about.
We’ve used them to do water uptake experiments. Capillary suction you’re seeing, or look at contact manual beating with products, some of which are supposed to be water repellent and some of which are to. We’ve looked at capillary suction, in this particular case, at an adhesive that was supposed to be permeable to water vapor and liquid water. As you can see after 4 minutes the liquid has risen to the joint that we glued and 3 hours later, the water still hasn’t moved any where. So much for the concept of liquid permeability. It isn’t there, it may be claimed, but it’s not really there. And so on.
We looked at strength and these are similar to the things we’ve just been talking about with respect to the previous lecture. This is one of those tiny, tiny cores, so you’re looking at a close-up in a machine of breaking strength. This is chisel splitting as a method of, it’s referred to as something like rock quarry index, I’ve forgotten what it’s called, strength index. Here another example of it in micro-abrasion. We just saw some micro-abrasion done. And here we’re looking at the same sort of thing, losses in the control being greater than losses in the treated material.
These are all laboratory techniques. All lab techniques and they’re terrific because you can fine tune them and get them to work. Pulse velocity ultrasound for example, and you see one of those cores in the jade right over there we’re measuring. We can do that in the field as well with portable instruments. But if we focus on the laboratory stuff, the real problem is that we’re still not looking at performance. And here if we make a single measurement immediately after treatment, we’re not looking at performance, because performance is long-term behavior in service. And the bad news is that we can only judge this by monitor.
Here’s the good news. We wait till the ending. The good news is that cemeteries because they’re arrays of typically stone and some other material outdoors, they lend themselves to monitoring by periodic inspection. Because they’re often in simple rows, we can number them or identify them through name, we could go back to them relatively easily. Another piece of good news is that if we do that we create a substantial amount of data on long-term product performance. At least we could if we all shared the information. And how can we share such information? By coming together again the way we are here today as a kind of a community.
Let me end on 3 problems, however, in the goal of this. Here is Hartford, the ancient burying ground in 1900. It’s all about performance and it’s nice to have documentation that goes back this far. It’s one of the most studied cemeteries that is here in the United States. Let me just use it as a way of identifying these 3 problems that I see.
First is how many of us do in fact return with some frequency to re-examine the work we’ve done? Here’s Irving and myself back in Hartford. Recent work in Hartford began in the early to mid 1980’s. We’ve been back in the ’90’s and again in the ’00’s, and again, as relevantly frequently. So we’re back there all the time to look at our work and to re-examine the work of others which is documented. But how often do we all do that?
Second question, or problem, and I’ll take responsibility for this. This is threaded nylon. I was very keen on the use of threaded nylon in the late 1970’s until they all began failing in the early 1980’s. I probably trained those people who chose to use threaded nylon. So question number 2 is, how many of us are willing to discuss our failures as openly as our successes? The Danish physicist Niels Bohr once said that an expert is someone who’s made all the mistakes that can be made in a very narrow field. I supposed by that token, I am an expert in the failure of threaded nylon. But most people do not want to get out and candidly talk about things that didn’t work well. Until we’re prepared to do that, we can’t have these kinds of reviews.
And then finally of these 3 questions, how many of us actually have the time to sit around and review years of data before we make up our mind? Before we make the materials and methods choice. Often we need to make that choice within a matter of weeks after we begin the project. Especially if it is a survey followed immediately by treatment. Sometimes we cannot sit around to do that. So I’ll show you what I … can I steal 2 minutes? I’ll show you just a whole sequence of that kind of thing as we attempted to do it.
Here’s a stone in Colebrook, Connecticut in 1998. It was then cleaned with 2 different cleaners, just in small areas, upper right, upper left. So that’s 1998. Look particularly at the area at the upper right. 1999 now on the right hand side. What’s interesting is the area below apparently getting a kind of wash-down from the [inaudible 00:20:44] is that the biological soil now is again dying, the miter is becoming progressively cleaner, so that’s in 1999. Here it is in 2000 where we’re getting re-soil in the clean area in the upper left, but no re-soiling the upper right. By 2001, we starting to see a little bit of re-soiling in the upper right. Nothing lasts forever, and the way the treatment which is biocidal and claiming to bio-static. This is all good news. The bad news is that later that year the town people responsible for the cemetery said they cleaned everything and the obliterated the test literally. So the test is gone.
I’m going to zip through some things just to talk about the kind of laboratory tests that we do, acid rain simulations, looking here at the effects of protected treatments. This is what the ACP treatment looks like on a particular English limestone, on the right hand side not treated, on the left side treated. Magnifications very considerable here. Fresco, you just heard a little bit about fresco with various stones and I just want to pause on this one for a second. Look at the sign on the left-hand side which is an English stone called reigate. A very misbehaving, odd kind of a stone. Not really a limestone, not really a sandstone, it’s a very peculiar hybrid material and the cube in the front that is so badly deteriorated has gone through freeze-thaw. The larger sample in the back is what you actually see in the buildings. So in this particular case by verifying that the same result is achieved with a laboratory simulation, you begin to say, “Well perhaps there are times when accelerated weathering works.”
I’m going to just show you a couple of these of some of the current work we’re doing with different kinds of methods of repair looking at issues of slate and slate temperature and fills. I’ll end on this one. This is in a cemetery in Scotland. It’s an amazing slide and I can only say, paraphrasing a television commercial, that is you have an erection that lasts … you should thank a limestone conservator. Thank you.
This paper discusses laboratory and field studies undertaken by the authors to determine and/or predict the effectiveness of a range of stone conservation treatments used in historic cemeteries. The techniques utilized to evaluate treatment efficacy range from laboratory instrumentation to inexpensive, low-tech procedures (such as tape testing) that are suited to being performed on site.
The choice of particular materials and methods involves a surprising variety of parameters, including ease of use, which is often related to the conservator’s level of skill. Manufacturers’ recommendations and product cost also play significant roles in the selection process. In most situations, the decision to accept a treatment (and to use it extensively) is only based on an initial sense of success, related to appearance upon completion of the remedial work, or to short-term behavior without obvious failure.
When systematic testing is done prior to product selection, another problem is encountered: the lack of deteriorated stone from which to produce specimens for comparative laboratory assessment. The authors will discuss the use of small specimens (derived from weathered building materials) in their work, presenting information on breaking strength and ultrasound measurement.
Ultimately, however, the key issue is that of performance, that is, long-term behavior in service. Most experts agree that the best approach to studying performance is periodic inspection. Cemeteries, essentially arrays of stone outdoors, lend themselves to this concept, if stone conservation efforts are thoroughly and systematically documented, and if we come together as a community to share information on product performance.
But even experienced practitioners seldom return to re-examine their work years later, nor do most of us have the patience to wait for such long periods of time to fine-tune our conservator’s bag of tricks. Accelerated weathering tests (such as freeze/thaw and acid rain simulation) will be reviewed in this presentation, and compared with observations.