Sadly jet washing will never get rid of your Black Spots, Reason? They are a living infection, when you come along and jet wash them, you’ve really only watered them and they love the challenge of gripping on and bedding down further. No sooner have you packed away, they start to reappear. Monty will seek them out and nip them off at the root, we’re not allowed to say “Kill” so we’ve eliminated them. You’ll notice they start to lighten in colour and fade away. The treatment you’ve just done should last 12 – 18 months. In this time, they find it very hard to germinate wherever Monty has been. When they do start to move in again, you’ll know exactly what to do combat the situation and only need a very light coating of Monty to move them out and keep it all fresh and clean.