Cleaning old tiles for reuse

[Andy Unique]

With these panel systems, if you use the sealing strip at the bottom where the panel meets the tray, what do you do at the point where you meet the shower screen? On a tiled shower the tiles/grout and bead of sealant between tiles and tray runs all the way behind the U section that connects the shower enclosure to the wall, where it meets with the vertical sealant between the U section and the wall tiles, but I don't see that that's possible using the trim.

Do you cut the trim to stop at the U section and just have a bead of sealant between the panel and the tray from there on out?

Sorry, I've watched quite a few installation videos but they all seem to end before installing a shower enclosure so they haven't provided any answer to this.