Table of Contents
i Quick Answer
LOSP and CCA are different treated pine treatment processes. LOSP uses a solvent-based carrier and is commonly used for above-ground applications, while CCA is a pressure treatment widely used for outdoor timber. The treatment name alone does not determine suitability; the hazard class, such as H3 for above-ground exposure or H4 for ground contact, along with the full product specification, determines the right timber for each application.
✓ Key Takeaways
- LOSP and CCA are different treatment processes. LOSP uses an organic solvent carrier, while CCA is a pressure treatment using copper, chromium and arsenic.
- LOSP treated pine is commonly used for above-ground applications, depending on the specified hazard class and product requirements.
- CCA treated pine has been widely used for outdoor timber applications, but certain high-contact uses have specific restrictions.
- The treatment type alone does not confirm suitability. The correct hazard class, such as H3 for above-ground exposure or H4 for ground contact, must match the project conditions.
- Timber appearance is not a reliable indicator of treatment suitability. Colour can vary, so always check the product label and specification.
- Cut or machined ends may require resealing because cutting can expose areas that are not protected like the original treated surface.
- Before purchasing treated pine, confirm the required hazard class, treatment type, structural grade, dimensions and relevant project requirements.
- There is no single better option between LOSP and CCA. The correct choice depends on the application, exposure conditions and product specification.
LOSP and CCA are two different preservative treatments used on pine timber in Australia.
Both help protect timber from biological threats such as fungal decay and insect attack, but they work differently and are intended for different exposure conditions. The right treated pine depends on the required hazard class, project specifications and applicable regulations.
This is where the comparison often gets confusing. Treatment type alone does not tell the full story. A product’s hazard class is just as important when deciding if it meets the requirements of a particular project.
What makes LOSP and CCA different?
The simplest difference is the treatment process and preservative used.
LOSP stands for Light Organic Solvent Preservative. It uses an organic solvent to carry preservative chemicals into the timber. LOSP-treated pine is commonly used for products intended for above-ground exposure, subject to the product’s specified hazard class.
CCA stands for Chromated Copper Arsenate. It is a pressure treatment containing copper, chromium and arsenic. The process forces the preservative into the timber, helping protect it from decay and insect attack.
Both are established timber treatment methods. Neither name, on its own, tells a buyer that a product is suitable for a particular structure.
That decision comes down to the complete specification.
How does LOSP-treated pine work?
LOSP treatment uses a solvent to carry preservatives into the timber. The treatment process is carried out under controlled conditions and is commonly used for above-ground timber products.
One noticeable feature of LOSP-treated pine can be its relatively natural appearance. The treatment process can also leave the timber with lower moisture content than some water-based treatment methods.
But there is a common trap here. Seeing “LOSP treated” on a product does not mean that it can be used anywhere outdoors.
The hazard class still needs to be checked.
LOSP-treated products are commonly associated with above-ground applications, with the exact suitability depending on the product specification. Where timber is cut or machined on site, the manufacturer’s instructions should also be followed for protecting exposed areas.
What does CCA treatment involve?
CCA treatment uses a combination of copper, chromium and arsenic to protect timber from biological deterioration. It is applied using a pressure treatment process that allows the preservative to penetrate the timber.
CCA-treated pine is often recognisable by its green appearance. Colour can vary, though, so it should not be used as a substitute for checking the product label and treatment details.
CCA has been used extensively in outdoor timber products in Australia. However, regulations place restrictions on certain applications involving frequent and intimate human contact.
This point matters for projects such as outdoor structures and areas where people regularly handle the timber. The applicable requirements need to be checked before selecting or installing a CCA-treated product.
Why is the hazard class so important?
The hazard class tells more about the intended exposure conditions than the treatment name alone.
Australian treated timber is assigned hazard classes based on the biological hazards and exposure it is expected to face. H3 is generally associated with above-ground outdoor exposure, while H4 is generally associated with outdoor ground contact.
That does not mean every H3 or H4 product is interchangeable. The complete product specification still needs to be checked.
This is the biggest mistake buyers can make when comparing treated pine. They see two products labelled with different treatments and try to decide which one is “better”. The more useful question is whether the product meets the hazard class and other requirements of the project.
Treatment and hazard class work together.
Does LOSP or CCA matter for decking?
Yes, but the answer cannot be reduced to choosing one treatment over the other.
Decking is exposed to weather, moisture and regular use, so the treatment and hazard class need to correspond with the conditions specified for the project. Different parts of an outdoor structure can also face different exposure conditions.
Human contact is another consideration. Australian restrictions apply to certain uses of CCA-treated timber where frequent and intimate contact is expected.
The timber specification should be checked before purchasing decking materials. If a builder, engineer or other qualified professional has specified a particular hazard class or product requirement, that specification should be followed.
What about treated pine for landscaping?
Landscaping projects can involve very different timber conditions. Some timber remains above the soil, while other components can be exposed to direct ground contact or prolonged moisture.
That difference affects the required hazard class.
A treated timber product should not be selected simply because it is commonly seen in gardens or outdoor projects. The exposure conditions need to be considered alongside the product’s treatment and hazard class.
This is particularly relevant for timber used around garden beds, fencing, outdoor structures and other landscaping applications.
The project requirements come first.
Does treated pine need to be sealed?
Cutting treated timber can expose areas that were not protected in the same way as the original treated surface.
For that reason, exposed cuts and ends may require an appropriate treatment or resealing product. The exact procedure depends on the timber and treatment. Manufacturer instructions should always be followed.
A separate coating or sealer may also be applied to treated pine to help protect the surface and maintain its appearance. It does not change the timber’s hazard class. This detail is easy to miss during installation, especially when timber needs to be cut to different lengths on site.
Can LOSP and CCA timber look different?
They can.
LOSP-treated pine can retain a more natural timber appearance, depending on the product and treatment process. CCA-treated pine is commonly associated with a green colour caused by the treatment.
Colour, however, should not be used to determine the timber’s suitability.
Two pieces of timber can look similar and still have different treatments, hazard classes or structural grades. Checking the product information is far more reliable than judging the timber by appearance.
What should be checked before buying treated pine?
A few details deserve attention before placing an order.
First, check the required hazard class for the exposure conditions.
Then confirm the treatment, structural grade, dimensions and any other requirements set out in the project specification.
For projects involving regulated applications, the relevant Australian requirements also need to be considered.
This approach avoids one of the most common errors in treated timber selection: treating the preservative name as the complete specification.
It is not.
Which treated pine should be used?
There is no universal answer to LOSP versus CCA.
The required timber should be determined by the applicable regulations, Australian Standards, project specifications and exposure conditions. The treatment method is one consideration within that process.
For a specified building or landscaping project, the timber should match the requirements provided by the relevant builder, engineer or other qualified professional.
For general purchasing, checking the product’s treatment and hazard class before ordering can prevent an expensive mistake later.
Need treated pine for a Melbourne project?
Timber Central supplies treated pine in a range of sizes, grades and treatment options for Melbourne building, fencing, decking and landscaping projects. The right place to start is with the required specification.
Once the treatment, hazard class, grade and dimensions are known, Timber Central can help identify the available products that match those requirements.
