Types of wood treatment

Why do we use treated timber?

Wood is a wonderful material to use for all kinds of structures. Warm, natural, durable and versatile. However, there are a few elements that can affect the durability of wood, especially if exposed to the forces of nature. The main factors causing wood to deteriorate are:

• different types of fungi
• insects, such as wood borers, termites and even
  marine borers and molluscs if the wood is submerged in water
• fire
• weathering

Because of these threats, it is important to protect wood from being damaged and to choose a suitable type of treatment process that will be ideal for your purposes.

Types of treatments used:

When it comes to wood preservation there are 3 groups of preservatives commonly used:

1. water-borne preservatives such as CCA (fixed) or borate (non-fixed)
2. oil-borne substances such as creosote
3. light organic solvent-borne preservatives

At die Pale Depot we mainly supply CCA-treated timber. However, boron- or creosote-treated timber is available on request. We also offer untreated wood. What do each of these types of treatments entail and what applications are they suitable for?

CCA-treated timber

CCA stands for copper-chrome-arsenic, which are all heavy duty wood preservatives. Copper is a fungicide and arsenic is an insecticide and additional fungicide. The chrome component acts as a fixing agent. CCA is applied to the wood by vacuum pressure impregnation. CCA-treated timber has a light greenish tint of colour, is totally odourless (unlike for example creosote) and the final product can be easily painted. CCA-treated timber makes use of dangerous chemicals during the process of treatment, but once these are absorbed into the wood they are no longer toxic, unless burnt. CCA-treated timber is ideal for applications such as roof structures, fences, gardening structures or wooden screens.

Boron-treated timber

Borates and boron compounds can be applied by using a dip diffusion treatment to green (freshly felled) wood or as a vacuum pressure process to dry wood. There is no colouring like with other types of treatment and the wood can be painted, glued or stained when dry. Boron treatment is environmentally safe, protects against insects and fungus and acts as a flame retardant. The chemicals used in the process remain water-soluble though, so this type of timber should mostly be used indoors. If used outdoors it should be in a place where the wood is not touching the ground and not going to get very wet.

Creosote-treated timber

In South Africa creosote and mixtures of creosote and coal tar solutions are used. Creosote is an oil-borne preservative which is applied in hot and cold open baths or in vacuum pressure impregnation plants at high temperatures. Creosote a very strong chemical which is toxic to fungi and insects and also highly water-repellent. Creosote-treated wood is very durable and weather resistant and can be used outdoors and in water even. The treated wood has a characteristic smell and a thick black or dark brown colour. Creosote is great for heavy duty applications such as electricity/ telephone poles, railway sleepers, bridges or wooden jetties, but should definitely never be used indoors.

Untreated timber

Of course there is also the option of not treating the timber at all. In many cases you might not require treated wood, because the place where you plan to use it does not require a weather- or insect-proof product. Or you could be planning to put a simple varnish or paint on the timber yourself. Untreated timber of course has no chemical smell or new colouration and is not toxic at all, but if placed outside will decay over time.

Choosing the right type of treatment for your needs:

In South Africa, the amount of exposure, which the wood will be subjected to, gets classified into different “hazard” categories. These help determine which type of wood treatment should be used:

• H0-I INTERIOR: Interior use only, for example mouldings or floorboards. Minimal insect and fungal protection needed.
• H1: Not applicable in South Africa, but applies to other countries which have no termites.
• H2 INTERNAL (LOW HAZARD): Also interior only for things like roof trusses and window frames. CCA and boron treatments can be used here.
• H3 EXTERIOR ABOVE GROUND (MODERATE HAZARD): For example outdoor decking, balustrades and garden furniture. Mostly CCA and creosote used here.
• H4 GROUND CONTACT (HIGH HAZARD): Fencing, pergolas or carports where the wood needs more protection as it goes into the groundand can rot more easily.
• H5 FRESHWATER (HIGH HAZARD): Exposed to freshwater consistently, such as jetties or walkways.
• H6 MARINE (HIGH HAZARD): Same as H5, but with saltwater.Only CCA together with creosote treatments will protect against marine borers and keep the wood from being destroyed.

In general, when deciding on what type of timber treatment you need it is important to consider the following:

• how much weathering will the wood be exposed to (which hazard level)
• how exposed will the wood be to pests
• how dangerous for humans and animals are the chemicals used
• what is the function of the timber

At die Pale Depot we focus mainly on CCA-treated and untreated timber products for the types of applications our customers are interested in. We are also able to supply boron-treated and creosote-treated wood on request. Our team is always available to discuss what type of wood product and what type of treatment you require for your specific project and we’d love to offer you our expert advice.