What happens if timber gets wet on site?

Brief wetting (rain shower, quickly dried) is generally acceptable — timber can tolerate short-term moisture exposure without permanent damage. However, prolonged wetting (days/weeks) causes: moisture content to rise above 20% (decay risk threshold); blue stain fungal colonisation (cosmetic, not structural); dimensional swelling followed by shrinkage on drying (distortion risk); and potential for incipient decay if MC remains above 20% for extended periods.

Brief wetting (rain shower, quickly dried) is generally acceptable — timber can tolerate short-term moisture exposure without permanent damage. However, prolonged wetting (days/weeks) causes: moisture content to rise above 20% (decay risk threshold); blue stain fungal colonisation (cosmetic, not structural); dimensional swelling followed by shrinkage on drying (distortion risk); and potential for incipient decay if MC remains above 20% for extended periods. If timber gets wet: unstack and re-stack with spacers to allow air circulation; cover from further rain; monitor MC until it returns below 18%; reject any pieces showing decay or excessive distortion.

Why this matters

This question relates to Timber Storage on Construction Sites: Best Practice Guide, which covers the broader topic in detail. Understanding this specific aspect helps architects, builders, and timber dealers make informed specification decisions.

For full context and additional technical detail, see our comprehensive guide:

→ Timber Storage on Construction Sites: Best Practice Guide

Related questions

• How should structural timber be stored on a construction site?
• How long can timber be stored on site before use?
• Do I need to cover timber with the sides open or closed?

About this answer

This answer is part of the PuurModulair Knowledge Base — comprehensive timber specification guidance for architects, builders, and dealers across the UK, EU, and Scandinavia.