To Do: Migrate


This project produced a video for training technicians in correct methods for preserving stone walls and rock fences. The video is a primary training resource, providing graphic instruction on how to repair, rebuild and relocate stone walls and rock fences. In addition to providing training to practitioners, the video explains fence and wall construction to archeologists, engineers, preservationists and conservators.

This video was made possible through Grant MT-2255-6-NC-23 from the National Center for Preservation Technology and Training (NCPTT). Download the closed captioned MP4 file below.


Speaker 1:     From New England to Texas stand monuments of scale, 200-year-old structures of rock and stone, the purest forms of craftsmanship laid dry without a drop of mortar. Fences and walls enclose the land. Dams and mills enclose the streams, strong enough to harness their power just from the way the rocks were laid. A single craft shape intricate spring houses and huge stone furnaces, all held together by friction and gravity, cleverly directed by the ingenuity of stone masons. In states such as Kentucky, stone walls trace a well-known signature across the landscape, yet less than 5% of them remain with many in disrepair. The Scottish and Irish migrant masons who brought us these skills are long dead and the craft they left behind almost faded completely with them, but not quite. With your interest and commitment, we can help conserve America’s past and keep alive the mason skill for future generations.

Richard:         I think we ought to start off by getting some of that off on that side and this right here, we can come into the road with it a bit. Do you see what I’m saying?

Speaker 2:     Richard?

Speaker 1:     Humbling stone walls in need of repair, too common a sight across the United States and an urgent priority for anyone with an interest in masonry.

Richard:         This wall here is typical of the type of damage that you can see as you drive around the countryside.

Speaker 1:     Richard Tufnell is a master craftsman and instructor for the Dry Stone Masonry Institute of America, a non-profit corporation dedicate to preserving the craft, its structures and history. He’ll be showing you the principles common to all walls and like you, he too was once a beginner.

Richard:         I certainly wasn’t a natural waller to begin with. I had after all been working in an office for some years, but when I moved to the country and had a house with many walls on it, I found that I had to get them repaired and I didn’t know how to do it. I asked a craftsman to come down and show me which, bless him, he did. After a winter’s practice and a little bit of dedication, I found that I could do a good job as well.

Speaker 2:     Richard, are we going to build this wall exactly like it is here or are we going to build it with a batter?

Richard:         We are going to certainly use the same style and design as these here, although we’re going to slightly improve matters by incorporating in an inward slope or batter to the design. That will make it a more stable structure overall.

Speaker 2:     Do we need to take the wall down below ground level for foundation?

Richard:         Yes. It’s very important to remove all stones as far down as they have penetrated the earth and then we will clear that out, level it and we will have a nice smooth surface to rebuild the new wall on.

Speaker 1:     Because the origins of masonry are as a grassroots craft, there are different approaches wherever you look with similar differences in terminology. Some people say walls while others say fences, both made from what some call rock and others call stone. Here are some variations of common terms. A-frames are the same as batter-frames. For foundation, there are footings or footers. There is packing or hearting, coping, copes and tops while throughs and tie-rocks are interchangeable.

There are common principles for all types of walls and walls that don’t have them are guaranteed to fall down. This cross section of a wall shows the key points. Every structure needs a good foundation and for walls, it is crucial. It’s the flat base that the wall is built on and is wide to spread the load reducing the pressure on the ground. The main body of the wall is built up course by course evenly on both sides. The space in the middle is carefully and tightly packed with smaller stones to create an interlocking network which binds together through frictional resistance. A loosely packed core is a common reason why walls collapse. Each course is set in a little from the one below so that the outer face of the wall slopes in like a narrow pyramid with each stone anchoring the one underneath. This is called the batter and directs the weight inward.

Halfway up, long stones are laid right across the wall and stick out a little on either side. These are called the throughs or tie-rocks because they go right through the wall and tie both courses together. By projecting out, they’ll continue to bind even if they are settling. Above the throughs, the courses continue with careful packing in the middle. The outer faces continue to slope inward to match the batter of the wall. The top course is then leveled off for a row of cover stones. These are a little wider and also tie the outer faces together. The wall is finished off with a heavy row of stones called the coping. They are laid on edge vertically or at an angle.

While it takes very little equipment to build a stone wall, here are some worth having: a three to four-pound masonry hammer, its handle should be one foot long for maximum power; a smaller hammer often used for trimming; a sledge hammer for breaking large rocks; chills, picks, shovels, crowbars and a wheelbarrow; strong string to set the lines of the wall, wooden pegs are the best way of holding the string tightly in rocks or dirt; a level and tape measure for precise measurement; the most important piece of equipment is called the A-frame or batter-frame and you’ll need two. Their profiles match the cross section of the wall and they must have straight edges. Their dimensions vary with the height of the wall.

For one that’s four feet high, the A-frame should approximately be three feet tall. Its base should be about 26 inches wide above the foundation, narrowing to 14 inches just below the cover course. When breaking rocks, flying fragments can damage your eyes. You can use your hand as a visor, turn your head away or best of all wear goggles, but whatever you do, you must protect your eyes. Think also about your colleague’s safety. Finally, protect your toes with boots with steel toecaps. Move heavy rocks carefully. When lifting a heavy rock, push your hips up against it so that the hips take the weight, then turn your whole body away. When picking up from the ground, keep your back straight, bend your knees and squat down before lifting.

Richard:         The way you dismantle an existing wall is very important. The coping stones as you see here are placed and taken separately and placed to the rear of the working area. The face stones are dismantled and placed on either side of the proposed line of working. It’s very important to break out the center of the existing wall so that the same amount of material is on both sides. You don’t want to have two-thirds of the material on one side and one-third of the stone on the other.

Speaker 1:     All stones should be carefully sorted into the different types needed for each stage of the wall and laid in rows close by. Set aside those that are more than two feet long as these are often hard to find and are needed as the throughs or tie-rocks and the covers.

Richard:         This rock here is actually long enough to be a tie-rock. Do you see how long it is? We’ll be needing one of these every yard.

Speaker 2:     We need something like 28 plus.

Richard:         About 28 to 30 inches would do. What we do with these is we lift them carefully and then we’ll just place them back out of harm’s way because the temptation is to shape those or use them as face stones when we need them to tie across the fence to bind the pieces together.

Speaker 2:     Will do.

Speaker 1:     Loose rocks and vegetation should be removed from the site of the new wall and the top soil skinned off until the ground is level and firm. If possible, tree roots should be taken out or they’ll undermine the foundations as they continue to grow.

Speaker 3:     Here it goes.

Speaker 1:     A deep footing is unnecessary. Just stamping down the earth in a level shallow trench will create a surface that is firm enough to lay the foundation. Using the pegs and string, mark out the site for the wall’s foundation course. This course is important because it distributes the weight of the wall over a wider area of ground. It’s also able to accommodate the slight movement of earth especially with freezing and thawing in winter. As the stones will be laid very close to the strings, the string height should be majored and set very carefully. The height of the strings above the ground is the thickness of the foundation stones. Try and gauge the average thickness of the foundation stones you have available. This will probably be between three and five inches. At last, we’re ready to start laying stones.

Richard:         The foundation course is crucial to prevent settling and therefore, we don’t want to use a mass of little stones at the base of the wall. We want to use big, flat, heavy stones that will be able to secure any weight that we place upon it. You want to also choose stones that are more or less the same height from the ground to the string. In other words, we more or less match the string. What we want to make sure is that we don’t in any sense touch the string, but we work very, very closely to it approximately 1/16th of an inch. If you touch the string at all, you’ll have this effect. It will bow out and the whole line of the wall will be thrown out. If it’s too far in, then the next course above will overhang and that won’t work either. Here, you want to match it exactly.

We take flat wedged stones and we feed them carefully underneath and make sure that we work all the way around, checking as we go, that there are no gaps whatsoever. Even on this side, you just break little pieces of waste and tuck them home so that by the time you finished, you should be able to stand on that stone and there is no movement on it whatsoever.

Speaker 1:     The long side of the stones must run into the wall and be long enough so that more than half will be covered by the course laid on top. The upper surface might be laid horizontally to create a flat and level base for the wall above. The stones used for pinning should be flat and wedge shaped for the greatest area of contact with the ground. This evens out any settlement by spreading the load. You must avoid leaving holes. They will create pressure points on the ground and also puts stress on the foundation stones. Lay the foundation stones side by side, touching each other in an unbroken row. Never leave any gaps between them. When both sides have been laid, pack the center, filling the space completely.

Richard:         We then need to pack the center to make it absolutely solid and completely resistant to settlement. You do that by choosing the largest possible stone first that will fit the space and then you fill in with smaller stones until it’s more or less solid. If we take some of these pieces here, you will see that we can … We fit them in and we keep on taking pieces and working them in as large as possible to start with.

Speaker 3:     We could go down to smaller and smaller and smaller?

Richard:         Exactly. It’s terribly important that each stone is manipulated in to the tightest possible fit with those that are beside it. Never ever throw them in. They’re always placed and twisted and manipulated and squeezed until they get in …

Speaker 3:     These bigger stones inside, do they need to be pinned just like these?

Richard:         Only if there’s a big hallow on them. Yes, sometimes with a very big piece of packing, you need to put a further piece of pinning underneath it. But otherwise, just work down in size, twist, push, keep filling these little holes up. I cannot over emphasize the importance of packing well because the …

Speaker 3:     Locked together?

Richard:         It’s all locked together that the whole weight of the wall goes down on this and it is absolutely vital. You don’t stop. It takes probably longer to pack the middle than it does to find and lay the face stones well.

Speaker 1:     When finished, a good foundation will look like a well laid path. Now we set up the A-frames. They ensure that the sides of the wall slope correctly and must be set level. One alternative to A-frames is to hammer metal bars into the ground at correctly set angles for the slope of the wall. However, they’re a little more difficult to set accurately. Once level, tie the frame securely to rebar driven into the ground so that they cannot slip out of alignment during building. Set the strings for the first course of face stones. Tie them to each A-frame by winding them around the upright, five to six inches above the foundation and be sure to pull them tight once they’re in position.

If a wall is to be well built, preparation is all important. Never skip this in your enthusiasm to lay rock. The strings are now set and we’re ready to start building the first of the lower courses. But if you’re building into an existing wall, only one A-frame is needed. At the existing wall, set the strings at the correct height by pegging them directly into a sound part of the wall. Lay the largest stones first, keeping them level by packing underneath.

Richard:         I’ll tell you what Jaime, there’s an interesting point here. Remember that the wall slopes inwards. It batters inwards. It’s quite important the face of the stone, that is the one that is facing the string, actually also slopes in. If you notice here, you see it has a shape there?

Jaime:            Oh okay.

Richard:         What we need to do is to turn it over and place it along like that and that then follows the natural inward slope of the wall and that’s perfect. You had the right stone, but it was upside down.

Jaime:            Okay.

Speaker 1:     No matter what size wall you build, keep the batter constant, one inch inward for every six inches of height will give the correct angle of slope. This is common in well-built walls all around the wall. Again, lay the longest side of each stone into the wall.

Richard:         What we have here is a stone which we really need to turn so that it runs along way in.

Speaker 4:     Okay. Are we willing to sacrifice the antique outside for structural integrity? How much depth can we stand to sacrifice?

Richard:         I think that you need not worry over much about the weathering because the stones will weather down naturally and it is therefore much better to concentrate on the structural reasons for laying these stones in. If you lay them in that way, they tie and bind into the packing in the middle of the wall very much better than if they’re turned long ways. You can see that if you take a stone like this, if it’s long and narrow, it’s relevantly easy to tilt out. If it’s turned that way, it’s much more difficult. It requires a great deal more force.

Speaker 4:     The way that the rock above it holds the back end of the rock in instead of trying to pull it out.

Richard:         Exactly. It’s catching it and it’s gripping it with great friction and force and there’s no way that stone can move.

Speaker 4:     I see.

Speaker 1:     Lay the face stones touching each other and parallel to the strings, but note that it is not necessary to build level to the strings at this stage. Only lay one layer at a time on each side and always pack the core before you move on up to the next layer of face stones.

Richard:         There’s an old saying, each stone should do its duty by its neighbor. By that, they mean take a stone and set it down so it’s as tightly secured against all the other stones around it as possible. We take them one by one slowly and welt them down until you can’t move them into a better position so that they all settle down and they all interlock. Although there’s a little bit of movement, by the time you’re packing them all together, they’re locked up tight. That way, you will have a really strong wall.

Speaker 1:     The first course is now finished and the strings are raised another five or six inches. Continue building up the courses by repeating this process until half of the face courses have been built. The end of the wall is built up layer by layer at the same time as the courses, but as it requires extra stability, it needs some special attention. Its foundation projects out at the end of the wall also in order to reduce outward settlement. Alternate courses are set in line with the face stones and then across the wall so that they interlace in a dove tail arrangement. These stones are larger and have a more regular shape than those used in the rest of the wall. It means they’re hard to find and even harder to lay.

Speaker 2:     Does this look okay?

Richard:         Yeah, it looks fine. Did you have any special difficulties or …

Speaker 2:     Matching two stones on either side of the wall, yup.

Richard:         Right, right. It is very important though. You have to keep a nice level.

Speaker 2:     I’m trying to keep it level.

Richard:         The reason that it’s not battered and why we have a vertical wall here is a) it looks better and b) they’re very often set next to gate posts and so on so you have to have it … If it is vertical, you need to compensate with even extra strength and even extra care. This is principle of running back and forth is absolutely vital. I think we’re in a position now where you can try a single stone now to bridge all that into one.

Speaker 2:     I cut this and sized this. Finally one worked.

Richard:         That’s just great. What we need to do is we need to check first of all accurately that it’s centered. Richard, you give us a line on that. Let Danny know if it’s out of alignment in any way.

Richard 2:      No, that looks good. Maybe just [crosstalk 00:23:33] really not much at all.

Richard:         Get the level. You’ll appreciate of course with a wall head because of the slight irregularities of the stones. You can throw yourself off with the level. You take your average and as long as you get that right, it will look about fine.

Richard 2:      The level is on there. It looks good.

Richard:         It’s fine. It’s not twisted. It needs to come out a little bit. That’s it, that’s it.

Richard 2:      That’s fine.

Richard:         Okay. Now the way to continue, there are two ways you can continue here. Basically you can find another stone, again a single stone that runs along the front …

Richard 2:      Or two to go …

Richard:         Or two that run quite a long way in. You’re looking at this business of dove tailing it in. That’s absolutely vital. Do that and that will be great. Fantastic.

Speaker 3:     We don’t have a thatcher on the end so we need to do that.

Richard:         Sure, sure. Great. Absolutely fantastic. We’ll just fill that in and then work on the tie-rocks.

Speaker 1:     Lay the throughs or tie-rocks once the wall has been leveled off as close as possible to the strings. The height here is half the distance between the top of the foundation course and the bottom of the coping.

Richard:         We’ll just lift that into position, pop it down there. We try and cover our joints if we can. Then what we need to do, you can see that it overlaps well, what we need to do is to pack very carefully underneath so that the tie-rock itself is bound to the core.

Speaker 1:     The tie-rocks protrude by two to four inches on both sides and are a key design element that gives the wall strength. They’re placed three feet apart covering the joints between face stones wherever possible. As you work, pack each one underneath so that they are completely stable.

Richard:         Slide those into place. That’s excellent. They’re fitting nicely. Getting the wedges in. That’s it. We might have to trim that a little bit so we can put another face stone on. There we go. Now what we need to do is to just check, fairly firm pressure all the way around. That’s bedded beautifully.

Speaker 5:     Richard, does the tie-rock absolutely have to extend past the wall?

Richard:         It is traditional in some areas to lay in tie-rocks but to flash them off one face and have them extending the other, but that’s not the correct principle. The reason is that walls do tend to settle a little bit over time. It’s inevitable. In over 100 years, they will go down a little bit. If they move down, the tendency is for the two wall pieces to spread out a little bit. What happens then is that if these are laid and they project over on either side, they will continue to bind the wall together and it will last many tens of years longer. I’ve seen them tilted at angles of up to 40 degrees, but they’ve been saved from total collapse purely and because they’ve had really well laid projecting tie-rocks.

Speaker 1:     Raise the strings and fill the gaps between the tie-rocks with courses and packing. As more courses are added, the tie rocks will become firmly embedded in the wall. Continue building up the courses, raising the strings one more time. As the wall narrows in, smaller face stones will be needed which was why it was important to use the largest ones at the bottom. Be absolutely sure the joints are staggered. At all times avoid laying stones that touch each other directly above the joint between the two stones below. This is called breaking the joints.

Richard:         An unbroken joint basically is a line of weakness. You see how these stones here, the joints run all the way up, each of the stones is joined in together over the same spot whereas what we’re trying to do is each separate layer is to try and get a stone to break over the top of it. Where these stones are joined, we’re looking always to bridge over them with a single stone. It’s as simple as that. That way, we’ll avoid these running joints, these lines of weakness that run through the wall and obviously weaken it. Don’t put them in at all.

Speaker 1:     The wall head has been built up at the same rate as the wall and is now ready for its top end stone.

Richard 2:      Do you want to turn it? The other way.

Speaker 1:     This should be specially selected out and be a heavy cube so that it will sit securely anchoring the end. The face courses are now finished and the sloping batter can be clearly seen. Level off the wall exactly to the line of the strings before continuing on to the covers and the coping. It’s at this stage that there are the greatest number of style variations. Try to match the style of the existing walls in your region. If a wall is of particular historic importance, then you should try to maintain archaeological authenticity. Next, lay a course of cover stones. They’re laid in a row side by side and are wider than the course on which they rest. The cover stones tie the two faces together just like the tie-rocks below. Like the tie-rocks, pack each one carefully underneath before you lay the next.

When you press them, they should not move at all. If they do, they need more packing. The cover stones are quick to lay, faster than a layer of face stones. They also give a more stable base for the coping that will be stood on top and are recommended wherever possible. The coping is a row of stones that are laid on edge. The style can be a single row or pairs that overlap. Both can stand vertically or slope at an angle usually downhill. This is a type of single coping which is leveled off to the string. Lay a stone at each end so that the string can be set tightly at the required height usually about 11 inches.

The copes are then laid with their top edge as close to the string as possible, but not going above it. Any stones that are too low are raised by pinning with wedges on either side. These pins should not be too big or they will interfere with the next cope to be laid nor should they be too small or they could easily fall out in the future. Those that are too big, have their edges trimmed off so that when the wall is finished, the top of the cope stones will have a clean and accurate line. Lay vertical copes in a similar manner. Trim those edges that stick above the string and use wedges to pin and raise up those that are too short.

In both cases, the top edge of the cope stones should be close to the string. Whatever the style of coping, the stones must be locked off so that there is no sideways movement when the copes are shaken. This is done by hammering thin wedge shaped stones into the gaps at the top between the copes, but the coping must not move out of alignment. Because here we are rebuilding a section of existing wall, the top must be finished in the same style. This coping is double coping and slopes at 40 degrees, but there is no row of cover stones. For double coping, pairs of wide and narrow stones are laid in an overlapping pattern. Every three feet, a single cope stone is laid like a tie-rock to help tie the structure together.

Richard:         You see the principle here, it’s going to go right across. Now that’s a little bit high. Although it’s a random cope, it’s high enough to catch the eye. If we’ve got a fairly decent sized hammer … Have we got a cutting hammer? We’ll just take it off and I’ll try … hang on a minute … and then we shape it and slide it under the string carefully and that’s great. To make it of even height, we’ll just put another pin under there. That’s it.

Speaker 1:     Finally, the cope should be locked up tight with wedge shaped pins and then the wall will be finished.

Richard:         The principle of locking up is simply to brace each stone against itself so tightly that it won’t move and we do this by driving small wedges down in between the stones. But when you have many stones together like this in a double form of cope, then you must put them in at regular intervals and then tuck them in one at a time. If you try and put one in like that, you’ll force them apart. What you want to do is to put a line of these wedges in every so often, tuck them in gently one at a time and then start from the beginning and work again.

Richard:         What do you think?

Speaker 2:     It looks beautiful.

Richard:         It blends in really well. I can only see one fault to this wall.

Speaker 2:     What’s that?

Richard:         It’s not on my farm. Any questions on what we’ve done?

Speaker 5:     What’s for lunch tomorrow?

Richard:         Yeah, exactly. (Laughter)

Speaker 5:     Yeah, it looks good.

Richard:         Now the wall is finished, let us go through the key parts again. First of all, you lay a good level foundation, pack it carefully in the middle so that it is absolutely strong enough to be able to take this weight of the wall that is built upon it. From there, you lay the face stones layer by layer, course by course, carefully, carefully packing as you go. Halfway up the wall, you level it off and you put in the tie-rocks. These are to bind the two faces of the wall together. These are the 36-inch centers and stick out approximately two to four inches from the face. Make sure that you leave no unbroken or running joints. The wall is then continued on until it is leveled off at the desired height.

The style that follows depends on your area. There may or may not be a cover course, but whichever style is appropriate, lay the copes and make sure they are well locked. By remembering these key points, you too can get started. Remember, each stone has a specific job to do so think carefully every time you lay a stone. Good luck.

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