Tech memo - ELT protection and finishing systems

04 Sep 2026

Engineered laminated timber (ELT) – such as glulam and cross-laminated timber – was a major step forward for the building industry. Comparable to structural steel, but with the added bonus of significant environmental benefits, it also allowed greater design flexibility.

However, like all other timber-based products it is susceptible to damage caused by water, UV light and mould if left unprotected. If closed in within a few weeks then the risk of damage is minimal, but, if longer-term exposure to the elements is expected, a temporary protectant should be used.

There are a variety of different technologies available for such protectants and these should be selected with the finishing system in mind – as well as a supplier’s guarantee that the protectant used will be compatible with the intended finishing system. It can be extremely expensive to remove a deeply penetrated incompatible coating – assuming it is technically possible.

During the evolution of wood stains, there was a period when such products were designed to form a film on top of the wood to protect it from the elements. However, the high-level maintenance needs of such systems were often overlooked by homeowners resulting in unsightly and catastrophic failures as the coatings flaked off. As a result, the paint industry pivoted from products that merely formed a surface film to those that penetrated into the timber.

However, not all penetrating products are created equal. For example, mineral oil, also known as paraffin oil in America and Canada, is both penetrative and water resistant, however, nothing will stick to it and it can only be overcoated by itself. Once used, it is almost impossible to remove.

As a result, the wider paint industry does not recommend the use of mineral oils, or products predominantly based on this technology, as short- or medium-term protective coatings for ELT products. Likewise, Resene will not guarantee any of our standard systems over such mineral oil-based protectants.

Instead of using mineral oil, either unmodified or hybridised, we recommend:

• Following the specific recommendations from the manufacture of the Engineered timber
  
  
• Using plastic or reusable covers for short-term protection during transport and on-site to help protect ELT products during the prebuild stage
  
  
• Treating ELT products in the same manner as other timbers or plywoods: thorough sanding (the degree required will be dependent on the time exposed to the elements) and staining with a product like Resene Natural Wood Oil Stain (ideal for beams that extend through to an exterior exposure) or staining and polyurethaning with Resene Colorwood followed by a Resene Polyurethane (which should be preferred for ground level contact areas).

Yellow Post was named the Resene Landscape Tone-e Award Winner at the 2026 Resene Total Colour Awards. Project by: Elliot Western, Oliver Prisk, Andre Vachias, Henry Mabin and George Culling. Photography by: Sam Hartnett.

Published: 04 Sep 2026