How to clean a house exterior before painting

[Pineman]

I have to paint the outside walls of a house once the weather improves. It's been painted before and the walls are some sort of rough texture. The walls are in reasonable condition but the north-facing wall is covered in some sort of reddish algae or lichen. What I'm wondering is how to go about cleaning this off prior to painting.

The same stuff grows on the patio below and this can be pressure-washed off. This isn't really feasible for the wall though as it's huge, probably 30 feet high, and the algae is growing most of the way up.

Is there something I can put on to clean/kill it before painting. Also, what brands of masonry paint are recommended. It's on the west coast of Scotland and gets a bit of a battering.

 

[Alison556]

I used stuff that I got in Wickes when I did the outside of the house - I can't remember what it was though but some kind of fungicidal wash.

It was a slow process though. I'd get the wet weather gear on and pressure wash it - it's going to be easier to blast it with a pressure washer than it will be to try and wash it down with a cleaner (though I'd probably hit it with some fungicidal stuff as well to make sure there's nothing left to grow back)!!

 

[dcdec]

It has to be killed off. A bleach solution will do this but you have to ensure it doesn't get into the surrounding environment. It may be tyrolene (spelling) and a tint was added to it prior to application, its a real pig to paint and i won't do them anymore. If its your house you have no choice but if its a customer i'd walk away because if you don't kill the growth it will re-appear rapidly and you will get moaned at.

Bedec masonary paint is superb