I use a karcher vac for con roof inside, only have two per year
That I do but the vac makes it so much easier, you can really
Soak the roof without worrying about water flicking everywhere
When blading as the vac just sucks it all away.
Method
ApplyHot water with a little degreaser or detergent
Leave to soak
Scrub with white non scratch foam scouring pad for really
Dirty areas
Go over again with applicator and hot water same again.
Then vacum with karcher
Tidy edges with clean dry scrim.
Easy
;-)
Hope this helps