We have hardwood grooved decking that was treated with Osmo UV decking oil. This year the decking has large patches of grey (particularly those areas in the sun) – if I chip this grey off with my finger nail it comes off and the underlying wood is shown. I have tried Osmo wood revival to try and get rid of it but it is hard to come off. I have also tried weak paint stripper but it still won’t come off. I have tried pressure washing and it comes off with some real effort but not in the grooves. Can anyone recommended a substance suitable to remove this grey stuff?