If your walls look tired, cracked or patchy, the first question is almost always the same: do they need a full re-plaster, or just a skim coat over the top?
For a lot of rooms, the honest answer is a skim. A skim coat is a thin, fresh layer of plaster laid over the existing surface to bring it back flat and smooth. If the wall underneath is sound, still firmly attached and reasonably even, a skim is usually all it takes to get a paint-ready finish, and it is quicker and cheaper than stripping back to brick.
A full re-plaster is for when the surface underneath has actually failed. If the old plaster is blown, meaning it has come away from the wall and sounds hollow when you tap it, or it is crumbling, damp-damaged or badly uneven, then skimming over the top just hides a problem that will come back. In that case it is worth taking it back and starting again.
So before you book anyone, do the tap test. Knock gently across the wall with your knuckles. A solid, dull sound means the plaster is still bonded and a skim will probably do. A hollow, drum-like sound over a patch means that area has blown and needs more than a skim.
When we quote a job, this is exactly what we check first. We would rather tell you a skim will do than sell you a full re-plaster you do not need, and we would rather flag a wall that genuinely needs more work than skim over it and watch it crack again. Send us a photo or two of the walls when you ask for a quote and we will tell you straight which one your room needs.