Re-prime previously painted plywood hull?

I’ve recently bought a 1978 mirror in pretty tidy condition, a few little bits to sort, but mainly it just needs some paint and varnish.

The paint which is currently covering the hull has a few small bubbles, and seems as though it’ll peel and scrape away fairly easily, which is handy for me to take it off, but does this indicate that I should re-prime the plywood?

There seems to be nothing wrong with any of the wood, as far as I can see there is no damp or softness, and where I did peel a bubble away the plywood had clearly been primed, I’m just not sure if there is a shelf life for the primer nor when this ply was primed.

Am I best playing it safe, or can I save my time and money?

If it’s best to re-prime, should I remove the old primer or go over the top?

Sorry, lots of questions, but be gentle, it’s my first time.

PuffinInTegel's picture

If the hull plywood is sound, you can simply prime the sections where the paint has peeled, sand them down to the level of the old paint and then apply a new finishing coat. Depending on your expectations on the finish, you may have to do a lot of sanding or not.
There are sections of my boat'shull where the primer I applied years ago comes off very easily. The original primer has a silvery-grey colour and other paints don't seem to adhere to it very well. All the same, my paint jobs have held for between 7 and 10 years at a go. I'm no perfectionist and don't mind odd unevenness where old paint has not come off completely, my reasoning being that if it didn't come off, it's protecting the wood underneath.
Effectively sealing scratches that go right down into the wood is far more important and this may leave a surface bump which is difficult to fair without sanding into the wood again. But ensuring that water cannot soak into the wood is more important than having a faired, baby-bottom-smooth surface.
If you plan to keep the boat for longer, completely taking the paint down to primer level every 5-10 years and re-doing the complete job is advisable, if only to ensure that you have no bits of rot hiding under 3-4 layers of paint.
Cheers,
Gernot H.