Any suggestions on painting over tar?

It's old thin tar or bitumen on wood. In places it's soaked into the
wood and dried out. Elsewhere there's been repairs with more recent
tar more generously applied. I've scraped it down to wood but it's
still tacky. When I rest my weight on my palm while working here it
comes away with some tar residue which have to use solvent to clean
off.

Is there a hardener or sealant I should use or can I paint right over
tar? I don't think I want to use oil paint as the tar would likely
bleed through. But water based latex paint should not mix with the
tar.

Thanks for any adivce.