“Tanalised timber” is commonly used to mean pressure-treated timber, but technically the terms are not identical. Tanalised® is a trademark for timber treated with Tanalith® E preservative. Pressure-treated timber is the broader category.
Tanalised® specifically means timber treated with Tanalith® E
Arxada, the manufacturer of Tanalith® E, confirms that timber treated with this preservative is trademarked as Tanalised® timber. The word has become so widely used that customers often use “tanalised” as a generic name for any pressure-treated outdoor softwood.
Pressure-treated timber is the broader buying term
Pressure treatment uses an industrial process to introduce preservative into timber to improve resistance to fungal decay and insect attack. Different treatment systems and specifications exist, so two pieces of treated timber that look similar are not necessarily treated for the same end use.
Green timber does not automatically mean Tanalised® or UC4
A green tint is common on some treated softwoods, but colour alone does not prove the preservative system or Use Class. Genuine Tanalith® E timber can start green and weather towards honey brown and eventually silver grey; that colour change does not by itself mean the preservative protection has disappeared.
The end use matters more than the colour
For outdoor timber, check what the product is intended to do. Timber used above ground and able to dry has a different exposure from timber in permanent ground contact. Read UC3 vs UC4 Treated Timber for the practical difference.
Shop by the job rather than the word “tanalised”
Browse Treated Timber for battens, rails, boards and posts. For joists and load-bearing framing, use the separate Structural Timber range.
Source: Arxada Tanalith® E guidance.
