Maintenance of Wood-Based Panels

Appropriate specification of plywood & other panels is the main consideration when using wood-based panels in exterior applications. Maintenance is then restricted to the renewal of surface coatings, the repair of edge sealing, the replacement of sealants and possibly remedial action on fixings.

Maintenance procedures for paint & similar surface coatings are well established and guidance on re-coating should be sought from manufacturers.

Below are a list of points that need to be considered in reference to maintenance for a given installation:

• Exterior coatings & surface treatments generally require redecoration every 3-5 years, depending on the level of exposure and elevation
• Wear and erosion of the surface & subsequent coating is more apparent on south and west facing elevations.
• As there are many different types of coatings available, guidance from the manufacturer should always be followed in order to achieve optimum results.
• The future appearance and durability of coatings will suffer if weathering of the substrate is allowed to progress too far as a result of neglected maintenance.
• Panels which have factory-applied phenolic-resin film, or GRP type coatings can also be repaired with patching compounds.
• Wood-based panels are susceptible to moisture ingress through both faces, and in particular, via the board edges, resulting in an increase in moisture content and consequent swelling of the panel.
• In plywood, exposed end grain and/or wood fibres at the edges facilitates moisture ingress. The presence of core gaps/veneer overlaps can create localised areas of ridging on plywood faces as a result of changes in moisture content. It is, therefore, imperative that all edges of all panels are protected if satisfactory performance is to be achieved.
• Moisture ingress can cause unsightly staining behind a translucent/clear finish.
  If wood-based panels remain wet in service for prolonged periods and without adequate ventilation or the drying effect of wind, fungal decay may lead to severe degradation of the panel.
• Water will penetrate into wood-based panels much more rapidly than it is lost by drying to air under normal conditions. This is particularly the case if its entry is localised, such as through an area of improperly applied edge sealant or large exposed core gap in plywoods. Under these conditions, water can be trapped for long periods behind fairly impermeable finishes, putting considerable demands on the adhesion between the wood substrate and the surface coating or finish.
• Continuous fluctuations in relative humidity can also be problematic, and cause dimensional changes to wood-based panels. Repeated wetting and drying of unfinished plywood panels can result in lathe checks opening up on the face veneer surface.
• UV light and sunlight will also cause a rapid change of colour of unprotected wood-based panels. Prolonged exposure will lead to general lightening/greying of the wood surface and a UV-protective finish is necessary unless a rough, bleached, weathered appearance is acceptable.