‘Throughs’ or ‘throughstones’ straddle the wall, connecting one face with the other. They help keep the wall from bulging outward as it settles by tying the two faces together into a single unit. This maintains the wall’s equilibrium by distributing the weight of upper layers equally onto both faces below.
The number and spacing of throughs shown in these diagrams ensure a very strong wall. Generally it is recommended to have a maximum of 30″ (750mm) between rows, and a maximum of 39″ (1m) centres between the throughs in any row. However, it is worth using throughs even if they have to be 6-10′ (2-3m) apart or more.
The patterns of throughstones vary considerably from area to area, and across stone types. See chapter 11 – Variations in walling for further details.
When placing a through, keep the following points in mind:
- Be especially careful when lifting and placing throughs. Your back and fingers are at risk.
- Use the longest and heaviest throughs for the lowest row.
- Before placing the throughs, bring the layer below level with the guideline, ensuring that the wall is the same level on both sides. If the through is sloping across the wall, the next layer will tend to slide off.
- Fill the layer well to make a secure bed.
- Place each throughstone with its flattest side down. Don’t wedge it, but shift it as necessary or adjust the filling if it doesn’t sit securely at first. The through’s weight must rest as much on the face stones on both sides, as on the filling between. Some wallers drop the throughs onto the wall from a height of about 2-3″ (50-75mm), to ensure they bed well. Care has to be taken to avoid trapping fingers and to drop it level so that the weight of the stone does not bear down on one side of the wall, possibly displacing it. This method is not recommended for large, heavy throughs, as it is likely to pose a personal risk, and is also likely to damage the wall.
- It’s important to ensure that the through crosses the joints on both sides of the wall.
- After placing the throughs at the correct spacing along the entire section, build up the wall between them with face stones and fillings. Choose stones that fit around the throughs, rather then shifting the throughs to fit the face stones. Continue to add succeeding layers in the usual way, using the tops of the throughs as beds for the stones above.
- If a second row of throughs is to be put in, level off the layer as before, and place the throughs so that they are staggered with the ones below.
Three-quarter throughs
Where throughs are scarce, it is advisable to use a pair of three-quarter stones as a substitute for a single stone. There are two alternative methods for setting three-quarter throughs, by placing the stones either adjacently or overlapping.
In the adjacent method, you carry out points 3-5 as for standard throughs, ensuring that each stone crosses the joints on its side of the wall. It is also important that you select a pair of stones which fit together well along their inside faces.
Some wallers place a third building stone, rather than hearting, over the joint between the throughs. It is thought that this distributes weight from above across both the stones, helping them to act as a single unit. If you do this, be careful to leave enough space on either side to place face stones which are sufficiently large to maintain the integrity of the wall.
In the overlapping method, you place one three-quarter through, following points 3-6 as for standard throughs. Then:
- Add another layer to the wall immediately opposite the first three-quarter through. This layer must be built to the same height as the three-quarter through, with the face stone touching the three-quarter through inside the wall. Build it in such a way that you avoid creating a joint when you place the next three-quarter through.
- If there are any small gaps between the second face and the three-quarter through, fill them with hearting.
- Place the next three-quarter through so that it crosses any joints and sits firmly on top of the first three-quarter through, with good contact along the length of its base.
Regardless of which method you employ, you must remember that three-quarter throughs are precisely that. If they are longer than three-quarters, then the stone used to build opposite will be too small. If they are shorter, then they are nothing more than a couple of good building stones, and will not bind properly.
Finally remember that three-quarter throughs are always used in pairs. Used singly, a three-quarter is merely a long building stone, and does little to bind the two sides of the wall.
