New answers tagged waterproofing
You don't have to use a backerboard on shower ceilings - especially if you aren't tiling it. You can drywall it. If you do use a backer board I would suggest Hardieboard. You would then just put a skim coat of joint compound (mud) over and sand.
Soldering is the usual method, but without metal-forming equipment I'd guess you don't have, that's not going to be a likely (or affordable) road to success for someone with no experience, for any value of large. Buy a galvanised washtub or trashcan is the direct, simple route to a watertight circular metal "pot" over a wide range of sizes. Move into ...
I would think that soldering would make a good seal provided you could keep the 2 surfaces tight to one another. Perhaps pop rivet the sides and the bottom together at 2" intervals, and let the solder flow. Yes DO be careful of any fumes may arise, but the galvanized metal may not get that hot enough to fume to get the solder to flow. Still, something to be ...
You can weld it but DO NOT breathe in the poisonous vapors produced when welding galvanized steel.
The easiest thing would be to fill the gap with UV resistant silicone caulk. Before you apply the silicone, make sure the join is very dry.
Top 50 recent answers are included