Skimming is a thin finish coat over something sound. Plastering is the whole job. Quoting for the wrong one is where a lot of jobs go wrong.
Skimming is a thin finish coat, around 2 to 3mm, applied over a surface that is already sound and flat. Two coats of finishing plaster, trowelled up smooth. It is what you want on a wall that is basically fine but tired, patched or a bit rough.
Plastering is the whole job, including the backing coats that build the wall out and get it flat before any finish goes on. If the wall is back to brick, uneven, or newly built, it needs plastering, not just skimming.
Skimming is a type of plastering. Every skim is plastering; not every plastering job is a skim.
The surface is sound. It just does not look it.
Old paint, minor patching, a bit of unevenness. The plaster underneath is fine. A skim brings it back to a flat, paint-ready finish.
Bonded and skimmed over is how most artex ceilings are dealt with. See can you plaster over artex.
New plasterboard is already flat, so it only needs the joints scrimming and a skim finish.
Walls that have been papered for years usually come up rough. A skim sorts it.
There is nothing sound to skim onto.
Bare masonry needs a backing coat, bonding or hardwall, to build it out and get it flat, before the skim goes on. Skimming straight onto brick does not work.
If the existing plaster is hollow, it has to come off. What is underneath then needs building back up. See why plaster blows.
A 3mm skim will not straighten a wall that is out by 20mm. It follows whatever is underneath. That needs dubbing out first.
Fresh blockwork gets a backing coat and then a finish.
Different job again, these need lime, not gypsum.
This is where jobs go wrong. Skimming is quicker and cheaper. Full plastering takes longer, uses more material, and generates waste.
If someone quotes you for a skim on a wall that actually needs backing coats, one of two things happens: either the price goes up once they start, or, worse. They skim it anyway. A thin coat over an unsound or uneven wall will crack, and it will follow every bump underneath.
So when you get a quote, it is entirely reasonable to ask: "is that a skim, or does it need backing out first?" A good plasterer will already have told you.
Tap the wall. Solid sound means the existing plaster is bonded, and a skim will probably do. Hollow, drummy sound means it has blown and needs taking off.
Hold a straight edge against it. A long spirit level will do. If the wall is roughly flat, skim. If there are big hollows and bumps, it needs building out first.
Not sure? Send a photo. It is one of the easier things to judge from a picture, and it tells you whether you are looking at a small job or a proper one.
The ones we get asked most.
Skimming is a thin finish coat, around 2 to 3mm, applied in two coats over a surface that is already sound and flat. Plastering is the full job, including backing coats such as bonding or hardwall that build out and flatten a bare or uneven wall before the finish coat goes on. Skimming is a type of plastering, but not all plastering is skimming.
No. Bare brick or blockwork needs a backing coat, typically bonding or hardwall, to build the surface out and get it flat. A 2 to 3mm skim coat applied directly to masonry will not hold or look right.
No. A skim coat is only 2 to 3mm thick and follows whatever is underneath it. A wall that is significantly out of true needs dubbing out or a backing coat first. Skimming an uneven wall simply gives you a smooth, uneven wall.
Yes. Skimming is quicker, uses less material and creates less waste than full plastering with backing coats. This is why it matters that the job is quoted correctly, a skim priced on a wall that actually needs backing out will either cost more once work starts, or crack if it is skimmed anyway.
Tap the wall, a solid sound means the existing plaster is bonded and a skim will likely do, while a hollow drummy sound means it has blown and needs removing. Then hold a long spirit level against the wall: if it is roughly flat, it can be skimmed; if there are significant hollows and bumps, it needs building out first.
Send a photo on WhatsApp. We'll tell you straight, even if the answer is that there's nothing wrong.