Bitumen.

[zabado]

I'm going to paint some black bitumen on lower areas of my shed that's letting damp through, but my shed is painted with grey Cuprinol wood preserver. When the bitumen has dried will the Cuprinol still adhere to the newly painted bitumen.

[The Builder]

Not very clear what you mean, Zab.
I guess you want paint the lower area with bitumen, then overpaint it with the Cuprinol?

The Cuprinol is most likely water-based, so it's not going to be compatible with bitumen.
Bitumen over Cuprinol would probably be Ok, but the final coat of preserver is not going to sit comfortably on the bitumen.
Bitumen by all means, but just leave it uncovered.

[zabado]

Thanks Builder. My plan was to paint cuprinol on top of the bitumen to make all of my shed the same colour (grey), because if I put bitumen on the bits that are damp the shed will end up grey with patches of black bitumen. I think I'll see if they sell grey bitumen. thanks again.

[Stephen_G]

You'll never be able to hide it with the wood preserver. The more coats of wood preserver you go over it with might darken the colour and it would look odd. I would also second what The Builder said.