i will be installing a shower tray and wonder if it is best to tile to the floor and seal with mastic prior to installing the tray or, installing the tray and tiling up to the shower base leaving say 2mm for mastic between the bottom tile and the tray.
Fit the tray first. Sael wall above to about 500mm with unibond. Seal between wall and tray and then fix tiles. 2-3mm enough to get good seal between tiles and tray. Little extra effort front end will provide good water tight seal for many years. Remember to fix tray well so it does not moveat all and fix it level as it will have falls within the tray. That way the tiles look better and are a lot less hassle to fix.
Some shower base installation instructions specifically state that you should tile behind first and fix the base second. Unless yours says this I would install the tray and tile down to it, grout, and then seal the join with silicone sealer/mastic.
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