Timber posts are essential components of decks, pergolas and fences. What can you do to keep them from rotting away?
Rot is simply caused by fungi that see your timber structure as food. These fungi attach themselves to the timber and proceed to make a meal out of it. It gets even worse when the timber is damaged or cracked, as these hostile organisms find their way into the structure and cause more damage. Very soon the timber decays as it is consumed by the fungi.
Posts also bear a lot of weight due to the function they serve and the stress of carrying heavy loads can accelerate their deterioration. When you build your outdoor living extension in very moist areas or places close to water then you have the perfect recipe for rot — moisture, oxygen and food for fungi in the form of your timber materials.
There are some species of timber that are naturally resistant to rot-causing fungi, such as Ironbark, Tallowwood and Yellow Cedar. But the performance of these resistant species may be variable, depending on whether they are obtained from heartwood (which is quite durable) or from sapwood (which will not be as durable).
Your best bet then, to prolonging the life of your timber posts is to use treated timber. When properly treated, even the non-resistant varieties such as Radiata Pine and Mountain Ash can serve you well for as long as 50 years.
Timber must be treated to its optimum retention level and maximum penetration — the treatment needs to be fully absorbed by the timber deep into its structure. Otherwise, if the treatment stays only on the surface and the timber gets cracked or damaged, moisture and eventually fungi can get into it and cause it to rot anyway.
These references on the Softwoods website will help you learn more about timber treatments and the proper applications of treated timber.
There are a couple more techniques you can use to ensure the longevity of your timber posts. Using post shoes elevates the posts above ground and clear of any water. This is a surefire way of avoiding deterioration.
Setting the post into concrete also seems to help with its longevity. Concrete limits shifting, settling and lateral movements of the posts and may provide protection from moisture and shielding against harmful fungi.
When used with correct timber treatment, these methods can help keep away rot from your timber posts.