ᐅ What materials have you used for permanently sealing patio joints, and what are your experiences?

Hello,

we have a problem where the joints on our terrace were washed out during cleaning with a pressure washer and surface cleaner. We would like to re-grout the joints and want to use something that will last permanently this time.

The grout does not need to be water-permeable since we have a drainage channel at the end of the terrace. We have concrete patio slabs, part of which are laid on gravel and the extension on a sand/cement mix.

What can we use to permanently grout the terrace joints so that the material hardens and stays in place?