I do tend to swerve sealing, this is a good customer though.
I'm sealing a slate patio, brand new. I thinks she's wanting a guarantee for how long it will last, which obviously I can't do. All I can do is offer the manufacturer guarantee that the sealer works, and a guarantee that my workmanship will be of a high standard.
Anything other than that isn't possible. Just wondered what people did when asked this.
It's a fairly straightforward job, with very small joints so should be just like sealing floors we clean inside.