Rotten stuff from the timber and plywood deck of Antares. Scary, isn’t it?
Cornwall shipwright John Owles has issued a stern warning against timber-on-plywood decks: the commonly-used technique of laying timber decks onto a plywood substrate is doomed to failure.
‘Have one or the other type of deck construction but do not mix the two,’ he says to anyone considering a big repair and restoration job.
John makes his point on a web page reporting on restoration work he did on Antares, a 55ft schooner that was in his yard a little while ago. Her decks consisted of teak planking reclaimed from an old steamer laid onto a plywood substrate and payed with a polysulphide rubber – and the result was widespread rot.
The choice is clear, he argues: if you want a traditional-looking deck then lay a proper traditional deck using fully dried timber. Otherwise lay an epoxy-glass sealed plywood deck and paint it with a two-pack polyurethane sprinkled with glass beads for grip.
With timber on ply decks, it is almost impossible to achieve a good seal, even when the substrate is coated with epoxy.
This is particularly true where fastenings pass through the timber planking and plywood: ‘When a hole is cut in plywood it exposes 360 degrees of end grain, so every layer is at risk of absorbing water.
‘When moisture is trapped in these mid-layers where there is no air circulation, it is impossible for it to dry out… creating an ideal climate for any spores to become active and so the risk of rot is ever present.’
In building a deck, try to avoid anything that allows hidden water to hang around, he adds, and keep your vessel very well ventilated, especially when left unattended.
See John’s website here: www.rovcom.co.uk