Raised holes in walls occur in a variety of shapes and sizes, and for various purposes. Simple square and rectangular vertical slits are built in the same way as smoots. Round, triangular and cross-shaped holes are normally for decorative purposes.
Round
Round holes are also known as bull’s eyes, and basically consist of two semi-circular arches. The example here has four large keystones, but only the top one is essential.
To build a bull’s eye:
- Level the wall off to the height of the lowest stone in the bull’s eye, and then build up either side to the mid-point as shown. Place a 2 x 1″ (50 x 25mm) batten across the gap, ensuring it’s level. Pin a thin, pointed length of wood, called a trammel, to the centre point of the circle.
- Extend the wall on either side as shown. The exact size of the hole and the ‘smoothness’ of the finish will depend on the size of stones being used, both for the wall and for the bull’s eye. Small walling stone will give a smoother finish, better suited to using regular shaped, smaller stone for the bull’s eye. Larger walling stones will leave steps, which can be filled using larger and irregular length stones for the bull’s eye.
- Starting at the centre bottom, work out on alternate sides as if you were building an upside-down arch, angling the stones towards the centre of the circle.
- Complete the lower half of the circle. If they are part of the design, set ‘keystones’ at the horizontal, which will act as springers for the upper arch.
- Set up a former for the upper arch. For smaller bull’s eyes this can be supported on a pile of bricks set centrally. For larger bull’s eyes, a length of timber should be wedged in place, carefully set level.
- Complete as for building an arch. As with arches, the stones may span the wall, or a second bull’s eye may need to be built on the other side of the wall.
Triangular
Triangular apertures can quite easily be built using the technique of corbelling, in which successive stones protrude a measured amount beyond the stone below. However, you do need a sufficient supply of long stones.
If enough stones are not available, you can instead construct a triangle using three flat slabs to line the aperture. These should lap onto each other as shown, to give good stone contact. Some trimming may be required.
Take care with placing the first couple of layers, until the triangle is firmly gripped by the stones. Build the wall alongside the slabs as if you were butting up to bedrock, using the longer stones in the style of corbelling, although strict corbelling is not necessary as they will be held in place by the slabs. Finish with a stone sitting on the apex, as with an arch, to help lock the structure.
Whilst it is useful if the side slabs match the batter of the wall on both sides, it’s not essential. As long as the stones alongside the slabs overlap into the wall, all should be secure.
Cross shaped
X shaped crosses cannot be built out of dry stones, but ‘plus signs’ and crucifixes are relatively simple, provided you have plenty of long stones. The major limiting factor on size and shape are the stones available to form the top of the horizontal slits, and the dimensions should be planned with these in mind.
- Build the lower slit to the required dimensions as two mini wall heads. Finish the heads with either a slab or two to three matched stones which are longer than the proposed length of the horizontal slits.
- Build up the two ends of the horizontal slits, preferably ending with a tie rather than a runner.
- Level up the wall, and place the two slabs to form the top of the slit. More than half the length of these slabs, and preferably two-thirds, should sit on the stones below.
- Start the next layer of stones as shown, to anchor the slabs in position, creating a cantilever.
- Construct the heads on the free ends of the slabs, ensuring there is always sufficient weight on the fixed end to counterbalance. This means building the wall and then the head, contrary to normal practice, and a little care is needed to ensure a tight fit.
- Finish the feature with a lintel.
