How do I know if my timber is treated?

Determining whether timber has been treated can be important for a number of reasons. Treated timber has undergone a chemical treatment process to help protect it from rot, fungal decay, and insect attack. This makes it suitable for certain outdoor applications or for use in areas with excess moisture. Untreated timber does not have this added protection, so it is more prone to deterioration when used outside or in wet areas. Knowing if your timber is treated or not can help you assess its quality, durability, and suitability for different uses. This article provides guidance on the various ways to identify treated timber.

Look for stamps, brands, or tags

One of the easiest ways to determine if timber has been treated is to check for any stamps, brands, or tags that indicate treatment. Reputable timber suppliers will mark treated wood with information about the type of treatment applied. Here are some things to look for:

• Chemical brand names like “Tanalised” or “Wolmanized” stamped into the wood. These indicate pressure treatment with chemicals like copper azole or chromated copper arsenate (CCA).
• “Treated” or “Pressure Treated with…” stamps showing the wood has undergone pressure impregnation with preservatives.
• Colored plastic tags stapled to boards stating the treatment type and chemical used.
• Grade stamps with the letters “T”, “PT”, or “TRT” denoting different levels of treatment.
• Permanent ink stamps noting conformance to treatment standards like “AWPA U1” or “EN351-1”.

If you don’t see any obvious stamps or tags on the timber, it may be untreated. However, some treated products won’t be marked, so additional checks will be needed.

Look for a colored tint

Many chemical treatments impart a colored tint to the wood that can indicate treatment. Here are some common tint colors and what they mean:

• Greenish tint – CCA and other copper-based preservatives often cause timber to take on a greenish hue.
• Red/pink tint – Treatment with copper azole can give the wood a reddish or pinkish appearance.
• Blue tint – Micronized copper treatments result in a blue/grey tint.
• Yellowish tint – Treatment with borate preservatives may give the wood a yellow or honey-brown hue.

Keep in mind that some treated wood may retain its natural color. Newer micronized copper and organic treatments especially may not alter the appearance significantly. Don’t assume untreated wood based on color alone.

Check for perforations or incisions

Another sign of treatment is the presence of small perforations or incisions in the wood surface. These are caused by the pressure injection process forcing chemicals deep into the wood cellular structure. Look for evenly spaced holes or slits along the faces and ends of boards. The more holes, the deeper the chemical penetration. Perforations are a clear indicator the wood has undergone pressure treatment.

Assess weight and density

The chemicals used for treatment generally increase the weight and density of wood. Treated boards may feel noticeably heavier when hoisted. They are also harder to cut and drill compared to untreated wood. Weight and density can vary considerably though, depending on wood species, moisture content, and other factors. So while a hefty, stiff board is a good sign of treatment, it’s not fully reliable on its own.

Look for end grain penetration

Checking the end grain of a timber board is one of the most reliable ways to verify treatment. Turn boards on end and examine the exposed end grain closely. Properly treated wood will show colored treatment chemicals penetrated all the way to the center of the wood. Look for discoloration or dark streaks deep within the end grain. Full penetration to the core indicates thorough pressure treatment. If the end grain looks the same color throughout, the wood is likely untreated.

Try a chemical test kit

Simple test kits are available to check for certain wood treatments. These involve applying a chemical reagent to the wood surface and looking for a color change reaction. Test kits can detect copper, chromium, arsenic, and other active ingredients in common preservatives. While convenient, test kit results may not be completely conclusive. Surface chemicals can produce a reaction even if core penetration is poor. But used along with other indicators, they can help confirm treatment.

Ask your supplier

One of the simplest ways to verify if timber has been treated is to check with your supplier or place of purchase. Reputable dealers should have records of any treatment for the lumber they sell. Most will openly share this information if asked. For professional builders and contractors purchasing large quantities of timber, treatment documentation should automatically be provided. Getting confirmation directly from the source gives you definitive proof about treatment. Make sure to retain purchase paperwork showing treatment details.

Why is treated timber used?

Now that we’ve covered the main ways to identify treated wood, it helps to understand why treatment is applied in the first place. Here are the key benefits:

• Decay resistance – Treatment protects against rot fungi and mold growth that can destroy untreated wood over time.
• Insect resistance – Chemicals create a toxicity that deters termites, carpenter ants, wood boring beetles, and other pests.
• Moisture resistance – Treatment reduces swelling and structural damage to wood in wet environments.
• Longer service life – Treatment greatly extends the usable lifespan of wood exposed to weather, soil contact, or dampness.

These enhanced properties make treated timber well-suited for exterior applications like:

• Decks, porches, and pergolas
• Retaining walls and raised beds
• Fencing and outdoor structures
• Landscape projects

Treatment also helps protect wood used in high-moisture interior settings like bathrooms, basements, or laundries. Choosing the right treated timber helps construct durable projects that will stand up to the elements.

What chemicals are used for treatment?

Timber is treated using a range of different wood preservative chemicals and processes. Some common options include:

Copper azole (CA)

This is a mix of copper and tebuconazole fungicide dissolved in water. It is then pressure injected into the wood. CA treatment is effective, low-odor, and allows tinted or natural wood finishes.

Micronized copper (MCQ)

Tiny copper particles suspended in liquid are forced into the wood cells. MCQ treatment is cleaner, lighter-colored, and suitable for staining.

Alkaline copper quaternary (ACQ)

Combines copper and quaternary ammonium compound in a waterborne treatment. ACQ is widely used for residential lumber due to its efficacy and low toxicity.

Copper chromium arsenate (CCA)

CCA treatment uses a mix of copper, chromium, and arsenic oxides dissolved in water. While very effective, CCA use is being phased out over toxicity concerns.

Creosote

An oil-based preservative made from coal tar distillates. Creosote provides excellent decay protection but can leach toxins. Its use is restricted in many areas.

Borate treatment

Borates dissolved in water provide insect and fungus resistance. Borate treatments are low-toxicity and work for dry wood applications.

Knowing the different treatment options helps determine which is best for your needs while also considering potential health and environmental impacts. Work only with certified treated timber from reputable suppliers.

Is treated timber safe to use?

Wood preservatives guard against decay and insects, but some also contain metal pesticides and other chemicals that may raise safety questions. Here are some things to keep in mind regarding treated timber:

• Modern treated wood uses much lower chemical concentrations and less-toxic formulations than in the past.
• Leaching potential is reduced as treatments bond tightly within wood fibers.
• Taking precautions when cutting, sanding, or disposing of treated timber helps limit exposure.
• Use gloves and dust masks when machining treated wood to avoid inhaling particles.
• Wash hands after handling treated timber and before eating.
• Avoid using treated wood for cutting boards, countertops, animal bedding, compost, or mulch.
• When disposed, treated wood should be sent to approved landfills or recycling centers per local regulations.

While some people may still have concerns about chemicals leaching from treated timber, modern wood treatments are considered quite safe when used appropriately. Always check country regulations and follow manufacturer guidelines regarding handling and usage. Also look for timber treated with low-toxicity alternatives when possible. With proper precautions, treated wood poses minimal risks.

How long does treatment last?

Another common question regarding treated timber is how long the added protection lasts. There are several factors affecting treatment lifespan:

• Treatment chemicals – Some ingredients are more durable and resistant to leaching than others.
• Retention levels – The amount of preservative absorbed into the wood.
• Wood species – Less permeable woods like cedars take treatment less deeply.
• Use conditions – Constant dampness depletes treatments faster than dry environments.
• Sunlight exposure – UV rays gradually break down wood preservatives over time.

Under typical conditions, current pressure treatments last 15-25 years before chemical levels drop low enough to affect performance. Some treated wood remains protected for 30 years or longer. Periodic reapplication can refresh protection after the initial treatment expires. With proper maintenance, treated timber may only need replacing once or twice over the lifetime of a building or structure.

Conclusion

Identifying treated timber is relatively straightforward once you know what markings, signs, and properties to look for. This allows you to choose treated wood when you need enhanced rot, insect, and moisture resistance for building projects. While taking basic safety precautions when handling treated timber, you can feel confident using it thanks to modern wood preservative technologies that pose minimal risks when used as directed. Just be sure to source any treated wood from reputable suppliers who can verify the details of the treatment process and chemicals utilized. With quality treated timber and proper installation, your constructed outdoor projects will endure for many years to come.