I had terrible mould problems with a shower. The worst bit was the sealant around the shower tray which was mostly that tell-tale orange colour, and black in places. I have spent ages scrubbing with a toothbrush and neat bleach, which worked on the tile grouting, but didn't touch the sealant. I had to give up as I was going to spoil the seal eventually, and was resigned to replacing the sealant, and having to do it again every year or so. Then I read some good reviews for this stuff, and thought I would give it one last go. I am amazed - I have clean, bright, white sealant - and the whole shower looks like it's just been fitted. It was so easy as well - spray on, walk away for 30 minutes, come back, fall over with the shock of getting a brand new shower, pick yourself up and rinse it off. Absolutely no elbow grease whatever. It's now a real pleasure to get in there for the first time ever, as this problem existed when we moved to this house. It also worked wonders on a ceiling where we had a damp problem a while ago - black mould also vanished after leaving it for 30 minutes. 6 weeks later - no sign of it in either place. No doubt it will come back in the shower eventually, but I'm not bothered, because a quick blast with this stuff will shift it before it gets nasty. Yes it is strong stuff - but not so that you feel it's doing you harm. Open the window and walk away for frequent breaks if you have a large area to do like I did. I found it safe to use on the ceiling by standing on a chair and spraying at an angle so that it wasn't directly above me and couldn't possibly drip onto me. It wasn't dripping by the way, but you do need to be careful. Strongly recommended.