When it comes to protecting and beautifying the exterior timber of our homes or outdoor structures, paint seems like an obvious choice for many. Gloss paint, in particular, is favored for its shiny finish and apparent durability. However, the interaction between gloss paint and timber isn't as straightforward as one might hope. In this post, we'll explore the implications of using gloss or other waterproof paints on external timber surfaces.

Understanding the Nature of Timber

Timber is a natural, living material that reacts to its environment. Even after being cut and processed, wood continues to 'breathe,' absorbing moisture from the air during damp conditions and releasing it when the air is dry. This ability to adjust moisture content is crucial to the timber's longevity, helping it to resist cracking, warping, and other forms of damage.

The Effect of Gloss Paint on Timber

Gloss paint, renowned for its waterproof and durable qualities, seems like it could extend the life of timber by shielding it from the elements. At first glance, this assumption holds true. Gloss paint can indeed prevent water from penetrating the timber, shielding it from rain, snow, and ambient moisture. However, this benefit comes with a significant downside.

The very property that makes gloss paint effective at repelling water also traps moisture within the timber. If moisture finds its way into the wood through uncoated edges or via diffusion through the paint itself, it becomes trapped. Unlike breathable finishes that allow moisture to evaporate back into the air, waterproof paints create a barrier that moisture cannot easily pass through.

The Consequences of Trapped Moisture

When moisture becomes trapped within timber, it sets the stage for various problems. Here are a few potential outcomes of applying gloss paint to external timber:

  • Rot: Moisture is a critical factor in the development of wood rot. Trapped moisture creates an optimal environment for the fungi that cause wood to decay, leading to structural integrity issues.
  • Peeling and Blistering: As trapped moisture seeks to escape, it can lead to the paint film lifting off the wood surface. This results in unsightly peeling and blistering, which compromises the protective coat and necessitates frequent maintenance.
  • Swelling and Warping: Moisture alters the dimensions of timber, causing it to swell. Since gloss paint restricts the timber's natural expansion and contraction, this can lead to warping and distortion of the timber, affecting both appearance and function.

Alternatives for Protecting Exterior Timber

Given these issues, it's clear that while gloss paint can offer short-term protection and aesthetic appeal, it might not be the best choice for the health and longevity of external timber installations. Here are a few alternatives:

  • Microporous Paints and Stains: These products are designed to protect timber while allowing it to breathe. They enable moisture trapped within the wood to escape, reducing the risk of rot and paint failure.
  • Oil and Wax-Based Treatments: Natural oil and wax treatments penetrate the timber, providing protection and enhancing its natural beauty. These treatments need more frequent application but offer a healthier choice for the wood.
  • Regular Maintenance: Whichever treatment you choose, regular inspection and maintenance are vital. Ensuring that the timber can dry out after exposure to moisture will help to prolong its life and maintain its appearance.


While gloss paint may offer an attractive and seemingly durable finish for external timber, its use can lead to unintended consequences due to trapped moisture. By choosing breathable finishes and committing to regular maintenance, homeowners can protect their timber installations in a way that respects the natural properties of the wood. It's always best to consult with a professional when selecting products for your specific climate and timber type to ensure the best outcome for your project.