What type of adhesive is recommended for gluing metal brackets for a shower curtain rod to ceramic tile. I want to avoid drilling and using fasteners. The rod is an arched type that bows out to make the shower stall a little more roomier. Also, I don't want the ceramic to be damaged if the brackets need to be removed.
For a curved rod, with its substantial torque load (twisting force), not much short of epoxy or urethane will hold reliably. I just wouldn't do it since removing those things from tile would be a chore and may result in surface damage. Wall tile is often soft with a very thin glaze.
One other option might be to mount a bracket or plate above or alongside the tile, lapping it over the tile for mounting of the rod brackets.
I would definitely not even try the adhesive approach for mounting a curved shower curtain rod. I have seen so many of these now popular rods that were so poorly secured that they were sagging a good six to eight inches or about to fall down. Especially seen in motel rooms or b&b type rentals. In almost all cases they are using small mount points similar to these:
The just are not up to the added torque and strain that exists with a curved curtain rod. Add to that the rough treatment that can come from kids or other mishandling and the installation can look like a mess. Even if mounted into a stud or header blocking in the wall these types of mounts are not optimum.
What you should look for are rods that have spreader plates welded to the ends or even double rod units that have an elongated mounting plate offer better mounting options such as like these:
I was in a hotel not so long ago that had stone type tiles on the walls of the shower. Their shower curtain rod was curved out a lot but used welded stainless steel end plates that were in fact bonded to the wall with adhesive. I do not have a picture to show so I cobbled up the example below to show how large the end plates actually were.
None. You need to mechanically bond the shower rod in some way.
Just think about the daily stresses that the shower rod endures of opening, closing, and the occasional, albeit accidental, downward tug.
Any kind of adhesive strong enough to support this abuse for years is one that will likely be unremovable from your tile when you want to update your curtain rod.
Mechanically bond it to the wall or come up with some sort of ceiling-based solution.
Whatever type of adhesive you use will eventually fail and fail miserably for this use case. You will not only have a fallen curtain but you will have a big chunk of your wall torn out with it when it fails. You are in an environment that is hot and cold and steamy and dry, constantly.
You have two options:
If your tile goes to about 6-7' it is simple to just install a rod that uses tension springs. The ends sit above the tile and even if the tension fails a bit the rod just slides to the tile. This is the most common way I have put up curved rods.
You screw the rod cap into the wall. You can either go directly into framing (if you planned well), you can use anchors (least preferred), or if you do not have framing available using either a square molding piece or a shower flange to match the rod.
First cover the area with tape. I prefer duct tape - people disagree with me because of the gummy residue it leaves. Others use painter's tape.
The mark the flange holes on the tape. Note that when doing a curved rod installation there is usually a left and right side. Make sure these are put right and at the right angle that the curved rod needs to be in. For straight rods the only thing that matters with the flanges is allowing the entry to face up (if there is one)
I prefer a predrilling. So find a very thin bit you have and go through the tile. Too thin and your bit may break but just a really thin bit.
This small hole will provide a pilot for a larger bit. Proceed with size you need on non-glass tile. However if you are doing glass I would start with a very small glass bit and work your way up almost by size. For glass I may use 4 bits... yep. You do not do this for other types as a regular bit becomes "stuck" when going up incrementally and puts outward pressure that could cause a chip or crack.
When sizing your hole it should be bigger than your screw. If your screw is being held by the tile the chances are your tile will eventually crack. So you have two options here - you are going into framing (TOO LATE NOW BUT YOU SHOULD ALWAYS ADD EXTRA FRAMING FOR THE OUTSIDE EDGE OF A SHOWER OR BATH - I will often flip a 2x6 on its side to hold a potential glass frame or shower curtain). If you do not have framing you need to epoxy (glue) anchors in. If you do have framing you want to make sure screws will go in at least an inch.
The screws you got with the kit may not be up to snuff. Often I replace these with longer or thicker screws.
So you have your holes, you are going into the framing or using anchors. Put your flanges up. When screwing these in you should not tighten with mechanical drill. Get them 90% screwed in and then use a hand screw driver for the rest. Two reasons here. First if you over tighten you can crack tile. Second when applying a lot of pressure to a hand drill, especially horizontally in a weird space/angle it tends to slip and drill bit can scratch flange or tile.
If something going bad or there is a mess up... You can always buy an oversized flange, like below to cover the area. These often look great and can fix even big mistakes. Note that this area of shower has no "water issues".
You indicated in a comment that this is to install a curved rod. That's a problem because the curve introduces a torque to the brackets on the ends. My answer below assumed the brackets would have an almost straight-down force. Since this is a curved rod, I'm not sure that any "soft" adhesive would be viable. Soft set adhesives are easy to remove, but they won't be strong to a rotating or pulling force.
(written assuming a straight rod)
Based on your requirements, I would try hot glue. Use the stronger kind sold in hardware stores - not the cheap low-temp craft glue. In the future it can be softened with heat to remove.
Here is one example that I use for hanging things outside. Really any name brand should be fine, just avoid stuff that looks like its made for hobbies. Hobby glue tends to feel soft or gummy, is very cheap, and might be a store brand or have branding that makes it obvious that it's not for heavy duty use. The stronger glue feels harder in stick form and might be advertised for use in "heavy duty" or outdoor uses.