Ceilings are the job most homeowners underestimate, both in cost and in disruption.
The figure
MyJobQuote gives roughly £390 for an average room ceiling, and around £1,000 for a room and its ceiling done together.
A 4m by 3m ceiling is 12 square metres. At £390 that works out near £32 per square metre, well above the £15 to £25 skim rate for walls on the same job. The premium is real and it is justified.
Why overhead work costs more
Plastering a ceiling means holding a hawk loaded with wet plaster above your head while trowelling with the other hand, working off a trestle or hop-up, for hours. It is the most physically punishing work in the trade and it is slower than working on a wall.
It is also less forgiving. Gravity is working against the plaster the entire time, so the mix has to be right and the timing tighter. Ceilings show defects far more than walls do, because light from a window rakes across them at a shallow angle all day and picks up every ripple.
Preparation is heavier too. Everything below has to be sheeted or removed, because ceiling plastering makes more mess than any other part of the job.
Skim or overboard
There are two routes and they suit different ceilings.
Skimming over the existing ceiling is cheaper and quicker, and works where the old surface is sound and reasonably flat.
Overboarding, fixing new plasterboard over the old ceiling and skimming that, costs more but is often the better answer in South London's older housing. Many Victorian and Edwardian ceilings are still lath and plaster: timber laths with plaster pushed through to form a key behind. After a century that key crumbles, and the ceiling starts to sag and sound hollow.
You cannot reliably skim a lath and plaster ceiling that has lost its key. The added weight can bring it down. Overboarding screws through into the joists and takes the load properly.
Ask the plasterer to tap it and tell you which they are quoting for, and be wary of anyone quoting a skim on an obviously bouncy old ceiling.
Cornices, roses and mouldings
Original plaster cornice and ceiling roses are common in this part of London and they change the job. Skimming up to an intact cornice is slow, careful work, and running new cornice or repairing a damaged section is a specialist job at specialist rates.
If the mouldings matter to you, say so before the quote rather than after. A plasterer who has priced a plain skim and then finds decorative work has a legitimate grievance, and the alternative, a cornice clogged with finish plaster, is expensive to put right.
Living with the job
A ceiling makes the room unusable for the day and messy for longer. Plan for furniture out or fully covered, floors protected, and dust everywhere regardless of precautions.
Drying takes longer than a wall too, because warm damp air rises and sits against the surface you have just plastered. Ventilate properly and give it the full time before painting.