How to make outdoor walls last longer

Outdoor walls are typically built to last for many decades. But that doesn't mean you can ignore them. Here's how to keep them in tip-top condition.

Timber retaining walls are an attractive way to terrace a hill to create level gardens. Whether you are building one yourself or having it built for you, here are some guidelines to make sure your wall will hold up for the long haul:

• Install deadmen or tiebacks to make sure that the wall will stay in place. These anchors, with a short perpendicular section fastened to one end, help to prevent water and freeze-thaw pressures in soil from pushing the timbers out of position. Use large spikes to fasten the base of the T-shaped anchors to the wall in the third or fourth course at 2.5 metre (eight foot) intervals.

• For walls taller than 1.2 metres (four feet), install a second row of deadmen, six or seven courses from the base. Also be sure to slant the wall back into the hillside, about six millimetres (.25 inch) for each course.

• Backfill against the wall with gravel to facilitate drainage. There's enough space for water to seep between timbers so you don't need to provide weep holes as you would for a masonry wall.

Poor drainage behind stone and masonry retaining walls can allow water to build up immense amounts of pressure. If the saturated soil then freezes, the pressure will be enough to move or crack almost any wall.

Avoid this by installing drains in walls (perforated PVC drainpipes work well) and keeping them clear of debris and silt. Here are some other essentials to look for in a well-built masonry retaining wall:

• Provide a footing (a stable bed of tamped gravel, stone or concrete) for your wall. In areas where the ground freezes, the footing should be to the frost line — the lowest point to which the earth freezes in your locale.

• Lean walls 2.5 centimetres (one inch) for every half-metre (one foot) toward the soil you wish to retain.

• Use gravel as fill behind the wall so water can drain away and won't collect there.

• Keep the gravel and drainpipes from becoming clogged with soil and silt by using water-permeable landscape fabric between the gravel and soil (three sides, but not between the wall and gravel).

• Stone walls can last for centuries, surviving wind and storm. But it's often something as simple as a sapling that will bring them down.
• Don't allow plants, especially trees and vigorous vines, to get a foothold between the stones. It's easiest to pull them out when young; otherwise use your lopper.

• When building a traditional stone wall, either dry-stacked or mortared, don't forget to begin with a solid footing (tamped gravel to frost-line depth).
• Then start building with a large base, and taper the sides slowly inward as the height increases.
• Cap the walls with flat stones to help prevent damage from water infiltration and freezing.

• Stone walls, even those with mortar, are subject to the domino effect: Lose one or two stones because a car hits the wall or there is a freeze, and more stones will soon loosen.
• Replace a fallen stone as soon as possible to prevent a much bigger job later.