Moss growing on walls

[Krypton27]

Our property is a wooden frame covered by roughcast. The roughcast is sound but shows discoloration from seepage. There is some moss growing as well.
It could be cleaned and painted but we have been suggested Protex which is a one-off sealant. Any thoughts?
Thanks

[buildersmate]

I've answered on your other thread (there really is no need to duplicate questions).
When you talk about seepage, do you mean it is showing on the inside?