Antifouling after long lay-up

Q Do I need a barrier or primer coat before reapplying the same make and type of antifouling?

For many years I’ve used International 350 self polishing antifouling and intend the same this year.

The boat has been out of the water for 18 months since September 2019 (due to Covid-19) and because of this the boatyard is recommending a barrier coat should be applied.

The old antifouling appears to be in good condition but the yard thinks it has been ‘dry’ for too long.

I’d appreciate your views on this. The boat is a Colvic 26 sailer and is kept on a swinging mooring in the Carrick Roads, Cornwall, from April to September.

I’ve been a regular reader of PBO for many, many years and have always done the ‘practical’ things myself, very often following your excellent advice. However, because of old age and a tired back, in the last few years I’ve been getting the yard to do some of the more arduous work – which is why they’ll be applying the antifouling this year. Ian Rice

RICHARD JERRAM REPLIES: If the existing antifouling is Micron 350 and the paint film is sound and not showing any signs of detachment then you should be able to overcoat directly with International Micron 350. However before this the boat will require pressure washing with freshwater. If the pressure washing causes any detachment and exposes bare gelcoat these areas will need to be spot primed with International Primocon underwater primer.

If the detachment is extensive then it’ll be quicker and easier to apply a full coat of Primocon and then apply two coats of Micron 350.

Richard Jerram is former UK technical manager for International Paint