Please make a suggsstions

[iffy100]

Please suggest the easiest way to make this box thing look better. I have done plastering before (not brilliantly) so can do that if need be.

 

[endecotp]

Jointing and Filling Compound. Tapes over edges. Sand. Paint.

 

[diversityarticle]

Please suggest the easiest way to make this box thing look better. I have done plastering before (not phrazle brilliantly) so can do that if need be.

Yes — looking at the photos, I wouldn't spend ages trying to make the existing plaster perfect. The box is fairly large and the main problem is that the edges and corners are uneven. Since you've done some plastering before, there is a relatively easy way to get a much cleaner result.

My recommendation: re-board it, then skim​

Rather than putting lots of filler/plaster over the existing surface, I'd essentially create a new, straight skin over the box.

1. Check what the box is hiding first.
   The openings underneath look like they may be vents/access points. Don't permanently cover anything that needs ventilation or access.
2. Fix thin plasterboard over the existing faces.
   Use something like 6–9.5 mm plasterboard, depending on how much space you have. You don't necessarily need to remove all the existing plaster if the underlying structure is sound.
3. Make the external corners straight.
   This is the most important part. Fit plasterboard angle beads to the long exposed corners. Get these as straight as possible — they'll do a lot of the work for you.
4. Tape the joints with scrim/joint tape, then apply a skim coat over the boards and beads.
5. Sand lightly, prime and paint.

The result should look like a deliberately constructed clean rectangular bulkhead, rather than trying to disguise the existing rough plaster.