A Primer (probably not a Latin one though).

Quid et demonstrandum.

Okay, that's enough Latin.

Bones, thanks very much indeed for your lovely comment on the post 'Paint'.

What a relief! I re-read it and thought 'oo-er, that might be considered a bit patronising.'

I know from your writings in "Canal Boat" that you are a skilled DIY-er, so if I do stray inadvertantly into "I knew that" territory, then please forgive me..

Primer is the first coat you put on. Water-based, or acrylic, primer is formulated to be thin and has very good penetrative qualities, so it gets into the grain really well. However, it will warp MDF and plywood like nobody's business if only applied to one side, as the paint tightens the flexible board down one side as it dries.

It is quite safe to use a water-based primer on wood and then over-paint with oil-based under and topcoats. The water-based primers soak into wood much better than oil primers. This only works on wood though. You MUST use an oil-based primer if painting steel, and mixing oil and water-based paints willy-nilly on any surface will cause all kinds of trouble, so Bill Rodgers comment is quite right.

Undercoat is formulated to provide a good surface for the top-coat to stick to.

Under-coat is a solid-rich paint, unlike topcoat which is lots of varnish with a bit of pigment in it.

A good undercoat, then, is essential to provide 'body' to the final top coat.

It sticks really well to the primer, and if the correct shade is chosen, provides not only a stable foundation for the top-coat, but also contributes to the way light reflects off the topcoat, giving you the desired shine (matt, semi-matt or gloss).

I'm not sure where you are with the panels on The Good Ship.

If you've already put on a few coats of Crayola Paint and hate it, you can either sand it all back to nearly bare wood and start again, (which would be dispiriting and dull), or try Dulux Diamond-Hard Acrylic Eggshell.

This stuff may be the way forward.

It's not gloss. It's semi-matt in the way oil-eggshell is. But you can paint it over existing water-based colour coats with no fear. (It will need a 100 grit rub down to give it a good key, though.)

It is water-washable (unlike emulsion which is rubbish on boats), and is actually quite nice to apply. (Inhaling oil eggshell fumes in a confined space can give you bad headaches and weird dreams.....).

Your Dulux mixer shop will be able to mix Dulux Diamond-Hard Acrylic Eggshell to whatever colour you require.

As I say, this may be the way ahead. It's water-based, but it's so-oooo not Crayola!

Please let me know how you get on.

Cheers,

John.