This lecture was recorded during a symposium held May 13, 2006 at the Victoria Mansion in Portland Maine.
The Geology of Portland (CT) Brownstone, and Quarry Factors to Consider in Block/Slab Selection for In-Kind Replacement of Portland Brownstone
G. Michael Meehan, president, Portland Brownstone Quarries
First I would like to thank Robert and staff for their hospitality and Dr. Turner for some of the images that I will be using.
In 20 minutes I will cover 200 million years of geologic history and also factors affecting selecting stone at the quarry.
Much of what is fact 200 million years ago when there was one super-continent called Pangea, when all the continents were merged together. At that time they started to do their continental drift- to be pulled apart. The primary focus for our quarry, in Connecticut, Africa was adjacent to us and they started pulling. As it pulled it created rift valleys. In looking at where things were back when, the geologists have a technique of finding and it’s going to touch on a couple other issues we touched on earlier today.
If we were to look at a coastic sandstone, such as ours is, you have feldspar grains, quartz grains, a significant portion of metamorphic rock fragments, various types of cement, you have hematite, you have calcite, you have albite, and various clays and sundry things in there. Most of the grains though, the large grains, the staliptic grains like feldspar and quartz are iron stained, and the hematite has a magnetic orientation to it. When the sediments were put down that was encoded in the coding of the stone, so they would look at, if you look at the earth nearer to the equator the orientation is pretty low level and as you get higher in latitudes the dip increases.
If we go back, this is Africa over on this side of the blue line and this is the US. That’s the Bay of Fundy. That’s the Atlas Mountains over in Morocco and there’s the Hartford Basin. You can see we are at paleo latitude between 10 and 15 degrees, it was pretty tropical and arid.
As the continent pulled apart Connecticut itself got ripped in half, and the eastern and western part of the state got pulled physically apart. In the middle about 17-18 mile wide trough formed and you had to the east highlands, which this is current day so, but we would have mountains here and mountains here consisting mostly of metamorphic rock. We have shifts and ices were a significant portions of the storage rock for our stone.
As this was an uneven dropping, but on the eastern edge where we are the drops are more severe and so you have tremendous sediments rushing into this trough.
Here’s a plan view of the now eastern highlands and us, the western highlands and we are down here around Middletown, very close to this eastern border fault. Longmeadow would be right up in this area, a little further out from the border fault, it has some effect over how well the grains was stored in the Longmeadow.
These are the Longmeadows found, you can see very even grain, no discernible bedding, laying all over our stones, just have layers.
This is a cartoon depiction. This is probably where we kind of our in our current quarry. We have the mountains behind us, we have these big alluvial fans that are getting washed out during dramatic rain events; which basically in arid climates are these floods that just come pouring out and you’d have this tremendous volume of sediment coming out of the valleys and spilling out into this plain and what you wind up with is a real mélange of bedding styles and sediment in our quarry. You have relatively poorly sorted materials because they were kind dumped and the energy would drop quickly as you went further out to the bigger particles would do that that. Unlike a beach sand this material wasn’t washed up and run back, washed up and run back it was buried very quickly, so all the minerals that were in there didn’t get leached out they kind of became part of the cement and the fabric of the stone itself.
A modern day equivalent I’ve been told is in Death Valley where you kind of have a mountain scape up against a plain.
This is a view of the old quarry, and I’m actually in these trees that are no longer there but this is for perspective. The Connecticut River is here, this is 26 acres that were laid bare, which was all quarry. It’s estimated that 10 million cubic yards of material were moved, in this clip right here, which is was actually out along the river bank originally.
Due to, right here, a major joint system that was in the stone, due to the proximity of water, it was easy to quarry, it was easy to transport and it’s a beautiful stone to start with so it was very marketable at that time and that’s why the quarry developed there.
As far as factors to be concerned about in selecting stone from the quarry, this is the current quarry, well actually eight years ago, we’ve chewed through a lot of this now, but we’re on the upper ledges of the main quarry and there’s four primary factors I’m going to talk about. One would be rock size, grain variation, color and stippling.
We’ve quarried by the use of a diamond wire saw. This is a natural joint face, and actually we’re quarrying a rather long block, I’ll show you later. It’s about thirty foot long, part of it’s going to be used for the stair treads at the Victorian Mansion. We normally quarry ten foot lengths by five foot width but we do special cuts every so often so we are starting on this one here. We have a loop of diamond wire going through there cutting out blocks.
Once the blocks have been cut, we cut in one direction and turn to a right angle cut the others. We take an excavator this is about twenty three feet high about ninety tons of stone, and we start prying on it. There’s a half inch saw curve back there that our bucket gets in. It starts pulling it down. As it pulls down, there are bevy joints that start separating, and you can see there’s a little bit of sorting that happens just by the force of the stone falling down like that. Sometimes we have to take these blocks off and then plug them and feather drill them into even smaller sizes.
We then take the blocks, last year we put in a diamond wire saw for slabbing. We put it on a rail car, the blocks squared, sent in under the saw, the wire goes around, comes out makes a slice, we advance the rail car so we can get different slabs of stone in different sizes.
One of the problems we get into is with the dynamic bedding that’s in the stone, everybody once a nice slab, and the geometry of any blade is going to cut in a very linear fashion. Before I quarried this block, we squared it to the beds, but you can see here where’s there actually a seam coming through the other side. So the yield on this block, even though it might start out looking pretty for a piece of stone, you might only get six or seven feet coming across there on the stone in the appropriate thickness.
We then slab the stone and then we finish it. We do some finishing on site. Often we send blocks out to fabricators to slabbed off fabricators depending on the size and the time required on the project. This is a water table going into a home off one of those new McMansions that’s around Hartford.
This is where I hope Robert’s stone is laying, right in there. We’ve got the cut. We were there. We’re now down through it so on Monday, hopefully, we’re going to start pulling this long tower down. This is forty five feet, it’s about thirty feet where his stone’s going to be.
The second thing, the controlled size of the blocks besides what we’ve determined to be, is nature. This is that joint system. This is the joint face here, that’s a vertical joint and you can also see a horizontal joint that just comes up through certain beds. It’s a bit of a culprit when you’re laying out the geometry of your cuts, you need to factor in orientations to maximize the yield.
Here we see, this would be a ten foot length on a block that we had half cut, but there was a joint that intersected and that actually the joint would have started over here and aligned in that direction so we aren’t real happy about joints. We try our best to label them. One time I was stranded in the airport, I was watching security detection devices, so we tried a joint sniffing dog. It failed miserably but I got a good pet out of the deal.
In talking about selecting the stone, you need to determine if you want it naturally bedded, as a piece of veneer like this would be, or face bedded, which the majority of the veneer on the mansion is. In doing that what you’re doing is, we don’t have planar beds so much in our blocks so when you’re cutting flat, although you’re calling it cutting with the bed, you’re actually cutting across many different stratographic layers. It gives it that real pretty wood patterning but it also gives you the chance to get coarse grained blotches coming up, it’s that yield consideration.
I’m trying to show here some of the lateral variation in the stone. That’s a little bit of a channel. Here you can see bedding joints, this particular layer is a conglomerate and you can see how it’s holding moisture in particular. I think it’s cause this moisture intends to hang on, now why it doesn’t get rid of it quicker, I don’t know, but that conglomerate’s always moist. Above it there’s some, you can’t see it, but this is a really, I don’t want to say shale. It’s not a shale, but there’s more clay up in here and it will hold moisture too. We also find that the root zones from old plants you’ll see like, chloride stains from root marks.
This block is upside down. This is an example of a conglomerate scoured into a relatively finer grained piece below. This again controls how much yield you get from the stone because all you can do really, is cut from this level up. This stone in here is really lost. We block our blocks out the best we can, coarser grain, finer grain and again this block had particularly straight graining in it which was pretty good at that time. Frequently the grain will tip around a lot more than that. Here’s a finer sample of someone wanting some sculptural stuff that we’re trying to pull out but you can see this is actually a crack in the stone. The orange is kind of cracked, the blue line is are marked out as coarser grain but they’re actually medium grain but we’re searching for fine grain.
Color is the last of the concerns and here is a new piece we put in. This is years ago at Rhode Island School for Design but against the older stone you can see in passing we have a real variety of colors there.
Here’s Mark and Paul in Charleston, South Carolina where we put new pavers in adjacent to some old pavers they chose to save, with Georgia, that’s a good idea, we could start treating this for color, but this is a problem I’d like to talk about in our round table if you have any ideas. We have a lot of clients that want stone to look old instantaneously and being a geologist, you know, three, four decades isn’t much to me but to most clients that would be acceptable.
We have a carver who works in and out of the quarry from East Germany, and he had some mineral stains that he tried to do different versions of, actually I’ve got to write him about coating the brownstone, but again, maybe at the round table I’d like to hear more about that.
Finally scheduling, to everything there is a season and we quarry up until January and we come back the end of March typically, so that’s a concern when people are planning projects. General times, depending on the scale of the project and the degree of specificity of the grain variation that you can take, we might have great inventory or it might take six, eight, ten weeks for the quarrying process then you have to factor in the fabricating process, what your fabricators lead time is. It’s not uncommon for them to have six, eight, ten weeks depending on the time of the year.
In closing, we spent the day talking about the grand old dame of the Victorian Mansion and we’ve talked about her being nipped and tucked and lifted and I just like to leave you with the appreciation, that Henry often had, of the natural beauty of the stone. Thank you.