I would rather not use the SV7 for this. I don't think the steam nozzle will get the moss out of the joints. (And if it does, it will probably do so at a laborious minimum speed). I would rather use a traditional high-pressure cleaner than hot steam (with correspondingly less pressure). The SV7 is practical for tiles, windows, etc.. But for outdoor use, it probably just doesn't have enough pressure. Greetings Oli