When to use Untreated Timber

You love the rustic purity of untreated wood straight from nature, but you also realise that some structures need the protection of treated timber, so that they don’t fall apart and result in expensive repairs. When is it okay to use untreated timber and when is treated wood essential?

There are various factors to think about in terms of safety and practicality. The advantages of using treated wood are mainly that the wood lasts longer, especially when subjected to harsh weather conditions, insects and water logging. However, there are also instances where using untreated timber is definitely more suitable or where either one could work. Untreated timber costs less and is better for use indoors, in more sheltered spots or where people will come into direct contact with the wood.  

When should you NOT use untreated timber?

In the following instances it would be more advisable to use treated timber in terms of safety, longevity of the wood and practicality.

  • Use pressure treated wood in any situation where there is direct contact between the wood and moisture. This obviously includes constructions partially submerged in the water like a jetty on a dam, which would rot very quickly if not built with treated timber. (Saltwater structures need even more protection from the elements.) It also includes posts buried in the ground (like for a fence), or any timber that is heavily exposed to the elements like a carport.
  • When you need protection from insects, treated lumber is also very advantageous. Treated wood is resistant to insects like termites that cause huge amounts of damage, which can be costly to repair.
  • Treated timber can also be fire retardant, taking longer to catch on fire and burning much more slowly when it does. This is another factor to consider when choosing which type of wood to use.

(These types of applications usually fall in the categories H4 to H6 on the South African hazard classification system. Read more about this here.)

When can you use untreated timber?

Untreated timber is cheaper than treated wood, as it has not undergone the pressure treatment process. You may also prefer untreated wood as it is more natural and has not been treated with chemical substances and there is no colouring (like the greenish tinge with CCA) or smell (like with creosote). 

In the following situations untreated timber can be used:

  • For indoor use untreated wood is better as there is no need for protection against harsh weather conditions and the area is completely dry. Mouldings and floorboards don’t require treated wood and are also fairly safe from insects.
  • When people are in direct contact with the wood using untreated wood is better and safer. Use untreated wood for a foldable picnic table for example, where one might eat food that has been placed on the wood directly. Children’s toys or items used for serving food will also use untreated timber.
  • In some cases a combination can work well: For example using treated timber in the beams supporting a deck or for subflooring (which is hidden and covered by other materials), but using untreated wood for the surface area.
  • You can also use untreated timber for playground equipment, patio furniture or benches which are not overly exposed.
  • Untreated timber can also be used for gardening, such as making a raised garden bed, a flowerpot or mulch.

We stock a large variety of untreated and treated timber and can assist you with choosing the right type of wood for your project.

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