My father-in-law leaned on the towel bar to rise from the toilet, which ripped both sides out of the wall. The holes are pretty large, almost an inch on one side, and this is the second time it's been repaired (originally with mesh tape on the right side, and I think spackle on the left, the side with the larger hole. What would be the best way to mend this?
Towel bars are always reached-for and therefore always vulnerable. My approach is to make all towel bars capable of resisting the inevitable grabs and pulls.
In my house, the towel bars are all ADA-compliant grab bars, like this, mounted with wood screws into studs.
image from Google Images
Some are horizontal; these hold towels:
Some are vertical: no towels, but very useful for steadying and assistance when rising from the toilet. Vertical mounting sometimes permits placement on walls otherwise unusable for horizontal bars.
In addition, there are two vertical bars at the end of the tub/shower, so the user can move safely hand-over-hand from the green-towel bar into the shower.
The bars and mounts are sturdy. These have been in place without any issues for more than two decades.
The best option is to put backing blocks in the wall prior to drywall/ wall finish when building or remodeling a house. Of course, this is not always possible in existing houses.
Another option is to mount the towel bar to a 1x4 (or 1 x 6) piece of nice wood that you either stain or paint. Make sure you put good fastening for the wood piece into any studs you can find. The beauty of this is that if you make your wood piece big enough it will cover right up those ugly holes in the drywall and save you some time.
Prevention usually being better than cure, could the rail be put somewhere else - you admit it's for towels, not hauling yourself off the loo!
That solves one problem, but creates another - how does dad-in-law rise safely?
Need to open up the stud wall round the damaged area, to reveal a couple of strong uprights. Fix battens between them, in line with a proper grab handle - such as found in disabled public toilets - maybe two battens would be better. Then fix in a new piece of drywall to level the wall, keeping notes of exactly where the strengthened parts are - or use a wood finder, to establish where the handle can securely be fixed.
If that's the only towel place, the same idea will work - with the knowledge that towel rails are not generally designed to be grab handles.
The wall's already repaired once. I'd suggest cutting into the drywall and completely remove that whole area, including the previous patch. If you can remove the dado / wooden trim rails visible above, that will help cover the joints later. Or you might be able to sneak in there and cut it off, if that's not already a join between panels.
Once you have a good access hole, add extra framing in the back to support a good grab handle at both ends. You might choose to add additional 4x2 framing nods/dwangs firmly nailed to the existing studs, or a vertical backing board that spans a larger area and also secures to the studs on both side.
Remember this handle could be required to hold a hundred kilograms / 200 lbs of weight, so don't underdo it. Take a photo of the framing before you cover it up - can be helpful later.
Once the framing is done, resurface this area with a fresh piece of drywall and tape+plaster the joints. Topcoat the plaster, and sand to a good smooth finish.
Tape off the corners/edges and undercoat with a sealant suitable for a bathroom, then light sand and topcoat again with bathroom-compatible paint.
If you removed dado, then reinstall after painting.
Lastly, fit your new beefy-grade handles with enough stainless-steel screws to keep them secure under load. You might choose to use the handle as a towel rail, or separate the functions.
I kind-of like dual duty because the sides of the towel are apart so it will stay drier longer and saves space.
You can still use the room while this repair is in progress, so it doesn't all have to be done in a day.
This is a supplementary answer.
I'm not sure how often your father-in-law visits. Based on the frequency, you can decide whether to borrow or purchase. Here's the thing you need:
This has several different names, one of which is "Toilet seat riser with handles." These are also available without handles, but it sounds like handles would be a plus.
Where I live, you can borrow one for several months from the county "independence center."
There are towel bars that can hang from the top of a door. That's if you choose to patch the drywall but not put another towel bar in the same location.
This sheetrock will have to be fixed-- good recommendations for that already on here. But for future attachment, consider a MUCH heavier duty wall anchor, if you can't attach it to studs. I really liked the GeeFix anchors-- great anchors. They are newer, more pricy.
An advantage of these is that towel racks typically require 2 screws to secure each mount. You can drive BOTH screws into a single GeeFix anchor, so it's a bit more secure that 2 separate wall anchors.
It depends on how much time and money you want to spend and the result you want.
As others have said, a ADA bar would be a good choice if your father-in-law is staying with you and this is likely to happen again. Reinforcing with wood, and replacing the dry wall are good options but will take more time and money. You can use an app like Thumbtack to get bids from multiple contractors if you have more money and less time.
The simplest option if you just need a quick fix is to stuff the whole with wadded up newspaper and spackle over it again. Then reinstall the towel handle slight away from (above, below, or to the side) the repaired area with a pair of new drywall anchors from Walmart, Amazon, or the kitchen junk drawer.
A quick search on Youtube will also deliver many options with detailed instructions and visuals.