The wallhead and the curve are two of the most demanding single elements in stone work. Demanding both in terms of the building requirements as well as the work they do. While the middle section of a straight freestanding wall is relatively static , the curve and wallhead both work a little harder in their lives. The wallhead “holds back ” the wall from the forces of lateral thrust trying to push and overturn it parallel to the length of the building line.
The outside of the curve is subject to being “squeezed” or bulging outwardly. To counteract this natural tendency, in addition to proper building technique, tiestones or throughstones are a solidifying element to employ.
The curve may be laid out on the ground with rope, garden hose or PVC tubing. Fasten down both sides of the chosen material by pinning it into the earth with opposing spikes. This is the building line. Make sure than the building line of the wall is of uniform width along it’s length by tape measuring across.
One technique for finding the vertical line along the curve is with frames. Pairs of rebar aka “rerod” are driven into the earth opposite each other at the chosen batter ( slope of wall face). At the top of finish build, the rebar should be clamped firmly across the top with 2″x4″ or 2″ x6″. A total of 4 carriage bolts w/ washers and nuts – 2 on the inside and 2 outside spaced appropriately will squeeze the wood into the rebar.
In place of string line there are several choices for material to run between frames. One may use CPVC ( similar to PVC ) , rebar ( # 3 is 3/8 ” thick ) or the fiberglass / aluminum rods used by chimney sweeps. With the CVPC it is possible to use a piece of wooden dowel ( whittled down some ) as an insert to connect the sections.
Another technique for finding the vertical line is to fasten a wedge of wood cut at the appropriate angle to the level. Take your time and carefully lay out this “wedge” of wood. As well, the more accurate the wedge is – and the longer the level , so will increase the potential accuracy of the vertical.
One nice aspect of this technique is the wide open space to maneuver , versus working around the obstacle of frames and lateral connectors. The stone should be set just shy of the wedge when the level bubble shows plumb. This is the same idea as is expressed when one says the string line should “dance” – when used along a straight section. The string should be tight and always clear away from the stone.
The 1/16 ” or less distance away allows for the string line to be free to dance. Abiding with this discipline of the string line or wedge will result in a visually pleasing form all along the wall.
The builder may set the stone just shy of the wooden wedge on small faces. On larger wider faces it is possible to obtain 2 points of virtual contact ( almost) by moving or shaping the stone. Trimming the corners of wide stone employed on the outside portion of the curve will sweeten the overall line.
The last technique for finding the vertical is with an inclinometer. This is a level with an adjustable dial that measures slope and can also be adjusted for the desired batter of wall. This tool is convenient in that it is quick to set, is lightweight and is adjustable to your chosen angle. No wooden wedge is needed. The cost starts from about $ 60 dollars on upwards.
Written by Michael Murphy. Images by Brian Post.