Timber with low moisture content, where only the surface of the panel is affected, can often be dried passively by exposing it to air. This method is cost effective and does not require specialised equipment, but it is slow. Alternatively, active drying, where heated, desiccated air is blown onto the panel surfaces, is a faster and more commonly used method. However, it must be done carefully as forced drying too quickly can lead to further damage, such as cupping and gaps opening up between boards as the timber shrinks. Depending on the location, level of decay, and drying method, drying timber can take several months, as noted in the drying table by BMTRADA & Stora Enso 13 . After drying, shear tests should be conducted on small samples to ensure the panels retain their structural performance. If cracks have formed from moisture induced swelling or shrinking, repairs may be needed. Long-term exposure to moisture can lead to serious issues such as fungal decay and may require more complex and costly remediation. Four repair options are available – Dryout the affected area. – Replace one or more lamellas in a structural component. – Local repair where a localised section of a CLT structural component is removed and replaced. – Partial repair, where a structural component, such as a CLT floor or wall panel, is partially removed and replaced. – Full scale repair, where the affected component is completely removed and replaced. The approach needed will depend on the location and extent of the damage, as well as the type and orientation of affected structural components. A structural engineer should be consulted to assess the impact on structural performance, the design requirements for the connections and the need for any temporary works and propping. The repair strategy must address structural, fire, and acoustic performance requirements. For local and partial repairs to horizontal elements, the process typically involves removing the damaged CLT lamellas or sections, installing replacement lamellas, which are likely to be LVL or CLT sections, and then reinstalling any coverings or finishes. For vertical elements,
water damage typically occurs at the base where the wall is working in bearing. Repairs usually require cutting off the wall base (minimum 150mm) and forming a concrete or steel upstand to replace it. For full scale repairs of horizontal timber elements, ensuring proper access for the installation and manoeuvrability of new slab sections is key. This often involves temporarily removing glazing or façade panels to facilitate site access. To improve flexibility, it is recommended to use smaller CLT sections, such as 1-meter-wide strips. If a vertical element is extensively damaged and the damage is widespread, a full replacement of wall sections is necessary. Temporary propping will likely be required to support the structure during the repair.
DRYING OUT
LAMELLA REPAIR
LOCAL REPAIR
PARTIAL REPAIR
FULL REPAIR
Figure: Repair strategies for moisture contaminated timber
DURABILITY
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