Sanding uneven plaster - belt or random orbital?

[username132]

Another of my dumb questions: I want to sand smooth some uneven/bumpy plaster prior to painting it. I have a belt sander and a back-and-forth finishing sander; the speed of the belt sander is fixed and I'm concerned it might be too aggressive but I think the finishing sander is maybe a bit weak; would it be better get a random orbital sander? What would you do (other than removing the plaster and having it redone properly; it's been like this for 30 years or more but now mum wants it fixed).

 

[vinn]

Plasterers and painters used to sand everything by hand so use either power tool. Be very easy with pressure. Start the tool before approaching the work.
Do you know why its bumpy, or what might be under it?

 

[big-all]

without being funny
if you have never used a belt sander you will almost certainly finish up with a far worse surface with heel hollows and side grooves

 

[username132]

Plasterers and painters used to sand everything by hand so use either power tool. Be very easy with pressure. Start the tool before approaching the work.
Do you know why its bumpy, or what might be under it?

Hey. I've no idea why it's bump or what might be under it. I just figured it was plaster all the way back until brick. The internal walls are lathe and plaster, I think.

without being funny
if you have never used a belt sander you will almost certainly finish up with a far worse surface with heel hollows and side grooves

I've used a belt sander before but I figured that with a finer grit paper it might be controllable. I might be better off using the finishing sander with a coarser grit. It's got a really poor mechanism for clipping the paper in place but looking at pictures online, I see a lot of them using the same mechanism. The paper is always vibrating itself loose.

 

[big-all]

with a belt sander on the flat it weighs nothing gravity does the work with a little input to stop the heel digging in from a comfortable normal stance
on a wall you re holding the full weight applying force most off the time in strange constantly changing stances
it may work brilliantly but i wouldn't spend loads off extra money in the hope it works