The open grain texture of Oak will cause film failure. Varnishes are prone to failure when applied to Oak externally.
It is imperative that the grain is filled with coating before further coats are applied.
Oak is not as resistant to weathering as oily hardwoods and, therefore, needs better
protection when used outdoors. The large open pores make the problem worse providing
a route for water-ingress. Blue-stain mould spores are likely to be present on any piece of
timber and will be activated by moisture. Another problem with Oak is the high tannin
content, if not properly sealed water (rain) can wash the tannin out o
f the wood leaving a patchy colour and staining to the surrounding areas (bricks, patio, etc.).
Pre-conditioning to the correct moisture content is very important. If the Oak is outside
the moisture content range of 12-20% there will be excessive movement as it comes to
equilibrium. The wood can become split, and the coating film may also split exposing
bare wood, providing a route for water-ingress and rapid deterioration of the coating.
If this occurs remedial action must be taken immediately to prevent the wood becoming
weather-stained. Clean the surface and reapply sufficient coats of the same coating
product to fill the cracks/splits.
The coating integrity cannot be guaranteed on green oak.
Intense exposure to sunlight will cause gradual fading of the timber colour. A
pretreatment of Polyvine Wood Colour is recommended in these areas to enhance the
timber colour and prevent fading. Application to softwood, knots and resin pockets will bleed through the coating.
Inspect yearly for signs of wear or damage.
Clean surface thoroughly and wash off all cleaning solution.
A maintenance coat should be applied every 1 / 3 years on exposed areas, 3 / 4 years on
less exposed or sheltered areas.
New and weathered wood
New wood can be contaminated during preparation, or in the machine shop. Weathered
wood can already have contaminants on the surface.
All contaminants and millwork must be removed from the surface by sanding, 80/120 grit
for vertical, 60/80 grit for horizontal surfaces.
Fungus, pollen or spores not removed and trapped below the clear varnish will discolour
the surface of the timber when exposed to moisture. If contamination is suspected treat
timber with a proprietary preservative treatment as recommended by the
Previously painted wood
Completely remove old coating with 60/80 grit sandpaper.
Ensure surface is dry clean and free from dust, follow New and weathered wood