How to Build a Garden Wall
Unfortunately, there are no hard and fast instructions applicable to all types of walls. Much depends on whether your wall is to be free standing or retaining, the type ofon which the wall is built, the height and length of the wall, and the materials which compose it. Lastly, you should have a clear idea of what your wall is meant to do. If it is privacy you are after, there is no point in having a wall less than 1.5 m (5’) high, or the neighbours will still have perfect views into your garden. Although retaining walls (ie, walls that are built into the soil as part of formalized level changes) can look nice when quite small, say 30 cm (1’) upwards, dwarf free-standing walls serve very little purpose, either from the point of view of screening or , and they are still expensive and time consuming to build.
Free-standing walls should normally not be less than 75 cm (2’6”) high. The taller the wall, the more protection and privacy, but on the other hand, the more expense. It is very unlikely that you will need a wall 1.8 m (6’) or more high; walls of this height should not be attempted without professional advice.
The foundation depth varies from about 30-90 cm (1-3’) or more, according to the soil type and size of wall. Some soils, such as clay, present problems and require deep foundations. This is because the clay tends to swell in wet winters, and shrink or crack in dry summers, causing the foundations to shift and crack. Sandy soils tend to be less problematical, and the foundations can be relatively shallow.
Basically, foundations must be built on firm ground, and deep enough to escape damage from ground frost. If you are building a wall on disturbed soil, the foundations have to be deeper. If, while you are digging the foundation trench, you come across an area of old rubble or, dig it out until firm soil is reached and then bring it back to level with well compacted subsoil or foundation material. No matter how deep or shallow the foundation, never attempt to build it on topsoil, as this contains humus and other decomposing material and is bound to cause trouble; inert subsoil is a much safer foundation.
Brick and stone are the most common materials used for free-standing walls; although initially expensive, a well built wall will last almost indefinitely. Try to use local material, as this will be less expensive and also in keeping with the character of the area. If you are inexperienced, it is much easier to build a successful brick wall than a stone one, as the art of laying good stone walls requires much skill and experience.
Free-standing walls are best built 22 cm (9”) thick, 11 cm (4-1/2”) walls are sometimes built, but unless skilfully designed, they can be structurally weak and visually unappealing. If the wall is longer than 1.8 m (6’) piers should be built in at regular intervals for additional support. These piers, which are pillars of solid masonry built into the wall, are also necessary where the wall ends, say, where the gate occurs. Walls are usually finished with coping, such as slate, stone, special dense coping bricks, or pre-cast concrete units. Besides being attractive, they protect the top of the wall from rain. Make sure you select a frost-proof brick for outdoor wall building, as some bricks are too soft to be exposed to weather, and will crack if frosted.
It is important not to use cement mortar (mortar composed of a straight mix of sand and cement). The most common mistake of the do-it-yourself builder is to use a mortar which is stronger than the walling material. The wall is then too rigid to settle easily, but will instead develop large, ugly cracks. Pre-mixed mortar can be bought from ironmongers or building suppliers. If you mix mortar yourself, a good general mix is one part cement to one part sand to six parts lime (1:1:6).
Unless you are experienced at wall building, it is a good idea to consult your local building inspector prior to beginning construction; his advice may save you unnecessary time and expense, and ensure that the wall you build will be a sound one.