Timber walls where generally constructed in Australia around 1970’s & 1980’s originally from old railway sleepers. These were generally class 1 hardwood slabs, that were previously laid below railroad tracks.
Once they were removed from the railway tracks they would be on sold as landscaping timbers. We have found walls made of these type of timbers to generally last around twenty years. This type of timber has been getting harder to source in recent years, but is a very strong good quality timber when good sleepers can be sourced.
Then around 1990’s C.C.A. treated hardwood timber became more popular as a lot of people who had the old railway sleepers as retaining walls discovered that eventually termites would destroy the old railway sleeper retaining walls. People were commonly told by whoever was constructing the new wall or selling the timbers, that termites could not eat the C.C.A. H4 treated hardwood timber sleepers. We find C.C.A. H4 treated hardwood timber sleepers to generally last around 10 years in the ground.
Once timber wall owners began to find that termites do in fact destroy the treated hardwood sleepers, a new option was put forward by builders and landscape timber suppliers. CCA H4 treated pine sleepers. The biggest problem we have witnessed in recent years, is the use of timbers that are simply not thick enough for the job at hand. A lot of people in recent years have fallen into the trap of taking the cheapest price timbers they can find. Resulting in a lot of these new walls failing in a few short years.
When having a timber retaining wall built. You should expect to get what you pay for. If you are chasing the cheapest wall you can. Do not expect it to last as long as a well built and designed wall.