best prep for dirty masonry paint

[mattyfoo]

i've got masonry paint on pebbledash to paint. it's in pretty rough shape, could be worse, but loads of filthy bits and the odd spot of algae. i have a mate i can borrow a pressure washer off of. thought i'd pressure wash it (perhaps with bleach on the algae or algaecide) -- should I add in sugar soap and then go back and rinse? does the paint need to come completely clean or can i get away with just washed well? will it require hand scrubbing? hope not as it's a big house...

also, i've been told i might need to brush it with a stiff brush -- is this only if the surface is powdery? If i'm pressure washing do i need to brush, too? i have a stiff garden broom -- is that good

 

[JohnD]

If you spray the mildew with dilute bleach (a garden spayer will do it) a week beforehand, the mildew will be killed and will clean off easier when dead and dry

 

[Robbie uk]

No need to use sugar soap outside. Usually a good stiff brushing is all thats needed. Treat the algae with a algae soulution or neat bleech. If the surface is powdery then use a stabilising solution to bind the surface back.