You can get a scabbler head to fit in a kanga. I.ve used one many times works well on plain concrete a flail plane with th right flails in would be better for removing coatings and preparing the surface. Part of the work I did in the concrete repair game was specialist coating and floors.The machines may have changed over the years but I hired a floor grinder thirty years ago to try and remove a hump in floor and was really disappointed...it just polished the surface...it may work on your paint layer if you can stop it clogging. I still have the coarse grinding blocks I had to buy somewhere.
I learnt later that a "scrabbler" (which sounds a bit more aggressive than the flail machine @Jagare referred to) would have been better for my job...but the hire people advised badly/didn't have such a thing. I was told that scrabblers are used to resurface milking parlours, where the milk apparently rots the concrete surface, so they may be too aggressive for your purpose. Maybe smoothed with a grinder afterwards?
@Mike_E 's wire brushes sound like a good solution for paint.
You may be limited as I was by what your local hire companies have available...
That sounds good advice to arm the OP against the Hire shop, wish I'd known you thirty years ago.!You can get a scabbler head to fit in a kanga. I.ve used one many times works well on plain concrete a flail plane with th right flails in would be better for removing coatings and preparing the surface. Part of the work I did in the concrete repair game was specialist coating and floors.
25mm over 70 sq mtrs would see me getting in one of the big diesel planes we used to use. Or it may be better to cut round and remove the high section of floor and relay.That sounds good advice to arm the OP against the Hire shop, wish I'd known you thirty years ago.!
You sound like the man to ask.
What sort of depth of concrete can you remove with a scabbler / floor plane? I needed (still need, I never resolved the problem) to take off a hump/crown which was up to 25mm over 70m2. The result of a disastrous concrete pour which was thinned down to go through a concrete pump and as it was going in we suffered a deluge of a cloudburst. Never seen rain like it before or since. The concrete was then so wet it just flowed under the tamping beam.
It was an Everest polyurethane paint, I mixed it with a paddle mixer so pretty confident it was mixed well. I’m reluctant to etch as the paint supplier stated the ground floor was the preferred option for penetration over the etch…Depending how tacky the paint still is it would be best to scrape off as much as you can. Try a bark spade save all the bending. After scraping wipe over with a suitable solvent. Get your self a large angle grinder with a diamond floor grinding disc. After all the old coating is removed re etch the floor with hydrochloric acid. Let the floor dry and then re apply your coating. Was it a two pack polyurethane coating? Often its poor mixing or lack of hardener that cause it not to set. Poor degreasing and etching will cause the coating to lift
Those are good machines with the right flails in. The carbide flails are a bit heavy if recoating floors. I've use the same machine with carbide flails for resurfacing cattle yards so the cattle get a good grip.
I don’t know if I would be better etching or grinding - the floor was power floated and etched but when I spoke to the paint supplier they recommend grinding - I said to them that the procedure mentioned etching and this is why they agreed to supply the replacement paint FOC. I loathe to have to go and knacker a floor with a bad grinding job as it’s a fantastic finish at the moment other than the paint not bonding…I see they only recommend acid etching for self leveling and power floated floors. That makes sense. I have in the past use grit blasting or very powerful jet washers to remove the latence from concrete surfaces before coating.
A 180mm cup wheel is ok for grinding off high spots on a screed but they can be a bit aggressive and in inexperienced hands could quickly and easily dig into the concrete causing more damage.