Exterior Finishing
All fully exposed plywoods must be surface finished to prevent mechanical surface breakdown, known as surface checking or crazing, caused by the absorption and desorption of moisture through the surface veneer.
In addition it must be stressed that all plywood used in externally exposed conditions must be Type A bonded and preservative treated to ensure long term durability and performance.
Semi-exposed (outdoor living)
For ceiling linings of balconies or alfresco dining areas, clear finishing or staining is the desired choice. A good quality polyurethane finish has shown good results, bringing out the Hoop pine colour and grain. The plywood sheets should be properly sealed before exposure to the elements. The face, back and edges should have two coats before installation, with the face to have an additional finishing coat after installation.
Oil based finishes should not be used - the oil raises the grain, darkens any roughness and highlights swirls in the face veneer, leaving an aesthetically displeasing face. Visit the EWPAA website for a warning on oil based finishes.
Fully exposed (external cladding)
Smooth faced plywood is not recommended for external cladding, where the walls are fully exposed. Mechanical surface breakdown (known as surface checking or crazing) will appear, caused by the absorption and desorption of moisture through the surface veneer. A textured plywood face disguises these cracks giving a more desirable effect.
Exterior Paint Systems
The EWPAA has shown through full exterior exposure trials that 100 percent acrylic latex paint systems perform best on plywood. The satisfactory acrylic latex paint system for plywood comprises: 1 coat 100 percent acrylic stain blocking primer; 2 coats acrylic latex exterior top coat.
Rigid paint systems including oil based and alkyd enamel paint systems, are not recommended for use on plywood in weather exposed applications. Rigid paint systems form a hard brittle coat which is susceptible to checking from any movement of the plywood due to moisture or temperature.
For further information on exterior finishing, visit the EWPAA website.
Printable version of this page