Winter Issues for Timber Decking

Iron Staining, Moisture Movement & Other Problems

Winter is a tough time for timber decking. Moisture, temperature changes, and poor installation practices can lead to issues including iron staining, moisture movement, gapping and coating problems. In this blog, we discuss some common issues we see in the wetter months and how to avoid them.

Moisture Movement and Decking Gaps

Timber decking expands as it absorbs moisture. A 140mm-wide decking board can expand by around 0.5mm for every 1% increase in moisture content. By the end of winter, it’s not uncommon for boards to swell by 4–5%, or up to 2–3mm in width. If boards are laid with only a 3–4mm gap, they can close up entirely—causing cupping, surface damage, and long-term performance issues.

To reduce the risk, follow our decking installation guidelines provided with every timber decking purchase and allow for adequate spacing, especially in winter.

What is Iron Staining?

Iron staining—also known as iron oxide staining—occurs when metal filings or particles react with moisture and tannins in the timber. This creates dark, unsightly marks on the surface of your decking. We’ve seen this happen when metal grinding or cutting is carried out directly on the deck.

Avoid using power tools on or near the timber decking during construction. If metal filings do land on the boards, a timber cleaning agent should be used to remove any residue before applying a finish. If staining occurs after finishing, the boards may need to be cleaned back to raw timber and recoated.

Factory-Finished Timber Decking for Best Results

Pre-coating decking boards in a controlled environment like a factory, ensures an even finish and better protection. Applying a high-quality timber coating before installation helps seal the timber against moisture and improves long-term stability. Don’t forget to seal all cut ends on site as well.

Bowens offers pre-coating services for timber decking and cladding, providing the following;

• Protection on all 4 sides for added durability
• Minimises moisture absorption much more effectively
• Improves the dimensional stability
• Reduces onsite labour costs and speeds up project completion
• Reduces impact due to weather delays.

Timber Maturity and Stability

Today’s timber isn’t as mature or stable as it once was. Take the time to protect it properly, especially during winter. For more expert advice, visit our website for decking installation guides and recommended timber coatings.