The difference between a skim and a full re-plaster is one where homeowners are frequently offered the wrong specification, sometimes because the plasterer sees an easier or bigger job than the walls actually need. Understanding what each involves, and what the wall itself is telling you, helps make sure the specification matches the actual condition rather than the plasterer’s preference.
A skim is a thin finishing coat, typically two or three millimetres, of finish plaster applied over an existing sound substrate. It is the standard finish over new plasterboard, and it is also the right choice over old plaster that is structurally sound but cosmetically tired – hairline cracks, minor imperfections, dated textured finishes. A skim gives a smooth, ready-to-decorate wall without disturbing the underlying substrate. The right question to ask before a skim is whether the wall behind it is sound.
Full re-plastering means removing the existing wall covering back to the brickwork or blockwork and building the wall up again from a base coat of bonding or backing plaster, followed by the skim finish. This is the right choice when the existing plaster is blown – separating from the wall behind it – or where the wall has active damp problems that need addressing. A re-plaster is significantly more work, more mess, more time and more money, and it should not be recommended casually.
The tap test is the simplest way to check whether existing plaster is sound. Gently tap the wall with your knuckles across different areas. A solid, dull sound means the plaster is firmly attached to the wall behind. A hollow, drumlike sound in specific areas means the plaster has separated from the substrate and is essentially floating – it will fail sooner or later, and any decoration over it is temporary. A wall that sounds hollow in patches is a wall that at least in those patches needs re-plastering rather than Skimming and re-plastering.
Damp is the disqualifier to not skim over the top and hope for the best. Salts drawn from behind the wall by moisture come through the skim within months and appear as blooms on the fresh paint. Damp that has been getting into a wall for years often needs the plaster removing back to the brick, a salt-resistant plaster system fitting, and the source of the damp addressing. Skimming over damp is one of the most common short-cut mistakes and it never lasts.
Ceilings are their own category. Original Bournemouth ceilings in older properties are often lath and plaster – horizontal timber laths nailed to the joists, with plaster pushed through the gaps to form a mechanical key. Lath and plaster ceilings, when sound, are worth keeping – they perform better than plasterboard for sound insulation and have some character. When they start to sag or crack, the traditional fix was to remove them entirely and replace with plasterboard. A modern alternative is to overboard the existing lath and plaster with a thin plasterboard fixed through into the joists, then skim over. This preserves the original ceiling behind but gives a new, sound surface in front.
Artex and similar textured ceilings from the 1970s and 1980s are increasingly overboarded rather than removed, particularly because some older versions contain asbestos and disturbing them is regulated. A skim of finish plaster directly over an artex ceiling requires the artex to be sealed and bonded, and even then the results can vary. Overboarding with plasterboard gives a more reliable outcome and avoids any question about what the original textured coat contains.
The finishing quality between different plasterers is more variable than most homeowners realise. A properly-finished skim is glass-smooth, dead flat, ready to paint with no filler required. A less careful finish has faint trowel marks, minor high and low spots, and needs a coat of skim filler and rubbing down before decoration. The difference is entirely in the plasterer’s technique and how much time they take on the polishing stage. Ask to see a wall the plasterer has recently finished before committing to a job, especially for a room where you know you will notice imperfections in the light.
Cost differences between skim and re-plaster are significant. A skim on a normal-sized room is a day’s work; a full re-plaster of the same room is three to five days. Materials are more, waste removal is more, and disruption is more. Any local plastering team recommending a re-plaster should be able to explain specifically why – which walls are blown, what damp is present, what the substrate needs – rather than defaulting to the bigger job as a general recommendation.