Soil and Concrete
The steel material of Colorbond fencing materials is not designed for all landscaping purposes. Retaining walls need to shore up earth or concrete, and Colorbond materials are not ideal for that purpose. Soil contains chemical elements that can deteriorate the panels over time, while only galvanized Colorbond brands are suitable for use in concrete, which can also cause corrosion. This means that the timber section of the retaining wall needs to do the support work, while the Colorbond materials stay above as a decorative addition.
Alternative Methods and Supports
Timber is not always an ideal retaining wall material, but it does not corrode like Colorbond fencing. Properly pressure-treated wood can be strong enough to arrange in 1 or 2 feet of retaining wall above the Colorbond wall. This helps level property in low spots, but additional supports are often needed. When building your timber retaining base, use sleeper supports braced against the outside of the boards to keep the soil from eventually damaging the wall.
Retaining Wall Base
Wood is susceptible to moisture damage, so you need to dig a trench at least several inches deep and fill it with loose material such as gravel to provide proper drainage under your wall. The trench provides an easy way to measure for the posts that provide support for the timber wall. Post holes for the Colorbond fencing should be dug between 1 and 3 feet deep. Loose soils require deeper holes. It may help to pour a concrete base and set the Colorbond fence posts before filling the trench in with gravel for drainage and setting up the timber wall.
With the base created, the timber portion of the wall completed, and the Colorbond fence posts in place and level, you can connect the panels above the retaining wall. Three infill panels or sheets are commonly used, and the Colorbond posts and framework come with self-drilling screws and screw placement holes to make connection simple.