Today’s timber claddings are becoming increasingly fashionable in the modern building. Factory finished claddings and protective treatments under controlled conditions can offer significant extensions of maintenance cycles.

The selection of the timber species, design, dimensions and grain orientation of the boards, choice of fixings all play a major part in determining the ultimate service life, whist the quality of the site installation and fitting work is also crucial to the long term success of the project.

This information sheet on coating, installation, maintenance and storage gives key design points and must be read and understood before any installation takes place. All coating systems require maintenance to maintain their decorative appearance, it is therefore vitally important to recognise this when specifying coated cladding.

Opaque finishes have the longest maintenance intervals and are easiest to repair and maintain. Translucent finishes maintain the natural aesthetic appearance of the timber sub straight but allow more UV light to penetrate to the timber surface. This disrupts the surface, increasing stress on the coating film, which results in earlier coating break-down and requires more frequent maintenance.

When applying a coati ng to any timber the sealing of all exposed end grains are critical to prevent moisture ingress. Moisture ingress will result in significantly increased dimensional movement, mould growth, staining of the sub straight and ultimately adhesion failure.

  • internal and external mould details should have a minimum radius of 3mm wherever possible to avoid thinning of the coating on the edges
  • gaps or recesses in the cladding should be sufficiently wide (typically 3mm) to prevent the capillary draw of water
  • installation and building design must allow ventilation off the back of the boards and preclude moisture ingress. Under no circumstances must moisture content of the cladding board exceed 20% at any time.
  • only external grade fixings should be used preferably stainless steel
  • wherever possible, the design should incorporate a secret fixing. Moisture ingress through surface fixings will cause localised saturation and discolouration of the timber sub straight.
  • if nails are to be used large headed nails are more suitable, preventing the fixing pulling through the board in service
  • nail heads should be flush with the surface of the fixed board, if driven below the surface of the board; just apply the coating over the crack to prevent moisture ingress
  • all joints should be fully sealed and protected from moisture ingress particularly through end grain
  • failure to protect any exposed ends without the correct end seal will negate any claims. Most water ingress happens through unprotected board ends
  • any paint damage to the coated board should be repaired by application as per manufactures instruction
  • a ventilation gap should be designed top and bottom of cladding wall
  • if factory finished cladding boards are to be fixed through the face, a final site applied finish is required to ensure the integrity of the coating system
  • when materials arrive on site they must be protected from the elements. Site storage area should be well ventilated and not subject to extremes of temperatures.
  • all air tight packaging must be removed to allow ventilation
  • transported goods are packed into crates to avoid damage, on receipt boards should be re-stacked in a well ventilated area free from direct sun and rain until installation
  • left in original transportation pallets exposed to direct sun and rain could be liable to cross contamination without proper ventilation
  • all components awaiting installation must be stored under cover, preferably inside a ventilated building. Boards must be stored clear of the ground on level bearers, protected against dampness and direct sunlight. There must be space for air to circulate around the component.
Downing College | Cambridge
Westminster Abbey | London | June 2017
York University | York
The Painted Kitchen Ltd | Fife
Jurassic Retreat | Burton Bradstock
Lymm Fire Station | International Timber Ltd