A grab bar is only as strong as the material it is fixed into. The bar itself can be well made and still pull loose from a wall that was never built to take a load at that spot. Before you choose between doing the job and paying for it, find out what is behind the wall.
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Know what the wall is made of
Look at the surface where the bar will go. Tile over a backer board, a fiberglass tub surround, painted drywall, plaster, and brick each take different fasteners, and some cannot take the fasteners the bar comes with. Tap the wall to hear whether it is solid or hollow, and use a stud finder to look for framing or blocking behind the mounting spot. Find the framing before you drill, and mark it.
Read the rating and the fasteners on the bar
The packaging or instructions name a load rating and the fasteners the bar requires. Use those fasteners and no others. A bar rated for one mounting method is not rated for another, and a substitute screw or a plastic anchor that was not named in the instructions changes the rating even if it looks right. If the instructions say the bar must go into framing, a spot without framing is not a spot for that bar.
When doing it yourself makes sense
Do it yourself when you can find framing or blocking where the bar must go, the wall is solid at that spot, the instructions can be followed step by step, and you have the tools to seal the holes in a wet room. Seal the holes before the next shower, not after.
When to hire it out
Hire it out when the spot you need has tile that would have to be cut or moved, when a fiberglass surround has no framing where the bar must sit, or when you cannot find framing and the instructions require it. Ask the installer where they will mount the bar, what they will do with the tile, who patches any holes, and whether they will write down the fasteners they used. A written note of the fasteners is the record you will want if the bar is ever moved.
Set a check and name who does it
Each week, someone should press the bar by hand with a steady, careful push, not a hard pull, and look for movement, cracking at the wall, or a loose screw. Name the person who does this check, and name what they do if the bar moves: stop using it, tell the person who installed it, and do not rely on it until it is fixed.