waterproofing paint?

[solidarityplease]

Teacher here.
I need to repaint a sign painted on wood in the outdoor area of my nursery.
Really haven't got the funds to buy outdoor wood paint in multicolours: Is there a way I could use poster paint and mix it with anything to make it more weatherproof? PVA? Varnish? Or any other ideas?

Thank you in advance.

PVA softens and dissolves in water, so, no.

There is a fair chance, if you ask on Freegle or just around, people will have oddments of part-used paint to give you. Even if it has skinned over, you can often poke through the skin or cut round and lift it out (don't stir skin in) if you just need a small amount to do lettering. Old paint needs to be stirred very well, and may need a little white spirit or water (depending on type) to thin it. Plastic paint tubs seal better than metal tins so are more likely to be useable after being in the shed for a dew years.

How big is this sign, and how much paint do you need?

Thank you so much for your reply.
The sign is lettering, perhaps a foot high, about 10 feet across, not much really.

I'll ask around then, thank you.

Have you got a scrap store near you? They're an initiative where junk from factories etc is recycled (stuff like cardboard tubes rather than plutonium). Ours often has paint