CCA Timber treatment

Permacure CCA (Chromated Copper Arsenate)

CCA is one of the world’s most popular wood preservatives, in use for more than 75 years. A water-borne preservative, it offers timber long-term protection against attack by wood-destroying fungi, insect larvae and termites. It can be used for structural timber, agriculture poles (pine and eucalyptus) and transmission poles.

CCA is the oldest and most widely used wood preservative in the world. Many studies have found it to be the most effective wood preservative. Its broad spectrum of usage and its efficacy makes it a difficult product to replace, and it still offers the best value for money.

It has a service life of up to 25 years, although CCA treated wood can last for 40 years and longer.
CCA treated timber is odourless, safe and easy to handle after treatment, and requires no special equipment during installation.
We have been pressure treating timber to SABS Standards at Somerset Timbers since 1996 and use Permacure CCA treatment chemicals.

Treatment process

CCA is applied by impregnation into the timber by vacuum and pressure at our timber treatment plant. This approximately 2 hour process involves a pressure cylinder where timber undergoes a series of processes involving vacuuming and high pressure. It is a controlled process monitored by the SABS to ensure compliance with the SABS specifications.

Once the process is complete, timber is left slightly damp, but this carrier solvent (water) evaporates after a few days.

Technical details

The active ingredients are chromium (47.5%), arsenic (34.0%) and copper (18.5%). The extraordinary effectiveness of CCA as a wood preservative lies in the combined action of these three elements.

Copper has been known since ancient times and is one the most abundant metals in the earth’s crust.  It inhibits the reproduction of bacteria and also acts as a fungicide, preventing the growth of many fungi, including Lenzites trabea, Poria monticola and Lentinus lepideus.   Copper is used in CCA as a primary fungicide and bacteriostatic agent. It does not directly kill fungicidal or bacterial organisms, but prevents them from using preserved timber as a potential food source. During the preservation process, the bivalent copper ions bond to the cellulose and hemicellulose in wood via a redox reaction.

Chromium (often called chrome, though this is more appropriate when referring to the pure metallic state of chromium) is another abundant metal, known to have been used in ancient China by the Qin dynasty thousands of years ago for decoration and weapons manufacture.

When oxidised it has a bright red colour, which has led to its extensive use as a pigment and dye. It is also used an oxidising agent in many redox reactions and in analytical laboratories, among many other applications.  Chromium is essential to allow CCA to penetrate deeply into the wood, and for the arsenic and copper to form permanent bonds with the wood. The greenish hue of trivalent chromium can be seen in the pale green colour of CCA treated wood.

Arsenic has been known since the 13th century and has many uses as a herbicide, fungicide and insecticide.  Arsenic is used in CCA as a secondary fungicide, making the wood resistant to even copper-resistant fungi. It also functions as an insecticide, leaving wood resistant to attack from xylophagous and detrivorous wood borers.


Ideal for exterior and interior use when a relatively inexpensive treatment is required. It is water based and therefore is not recommended for products with a high tolerance fit e.g.. tongue and groove products. It leaves a greenish tinge to timber and therefore is not advisable for timber where an uncoloured finish is required. We recommend our Vacsol Azure clear treatment for this.

CCA treated timber is treated to H2,H3 or H4 classifications depending on end use. (see below) Different strengths of treatment chemical are impregnated into the timber depending on the end use (classification).

H2 Internal – low hazard:  Timber framing and roof trusses

H3 Exterior above ground – Moderate hazard: Decking, fencing, garden furniture, gates, external cladding

H4 Ground contact – high hazard: Fencing poles, Deck support poles

CCA Treated timber can be painted, although this is not necessary. If you choose to paint this timber, ensure that you use the correct type of paint.