Bad plastering is easy to sell and expensive to undo. Here are the questions to ask and the warning signs to watch for, from someone in the trade.
There is no licence for plastering. Anyone can buy a trowel and call themselves a plasterer, and plenty do. The finish looks fine for a fortnight, then it crazes, blows or cracks, and by then they have stopped answering the phone.
We would rather tell you how to spot that than have you find out the hard way. Some of what follows is uncomfortable reading about our own trade. It is all true.
The answers tell you more than the price does.
A lot of general builders plaster. Some are excellent. Many are not. A plasterer who plasters every day will give you a better finish than a builder who does it occasionally.
A proper answer mentions sealing the wall, PVA, Blue Grit, Bond-it or similar, depending on the surface. A blank look is a bad sign. Uncontrolled suction is the most common cause of crazing.
Skim is two coats of finish. If someone is quoting one coat, that is where cracking comes from. If the wall is back to brick, it needs a backing coat first.
External corners need angle beads. Anyone freehanding a corner is either very good or about to give you a wavy edge.
Plasterboard joints need scrim tape. It is not a guarantee against hairline cracking, but skipping it guarantees it.
Cob, lath and plaster, and lime are different jobs entirely. A good modern plasterer may be genuinely poor on an old Devon wall, and should say so.
None of these are absolute. All of them are worth noticing.
A proper quote says what is included, prep, materials, how many coats, waste removal, whether skirting comes off. If it is just a number, you have nothing to hold them to.
Materials money is reasonable. Half the job before a trowel has touched the wall is not.
A good plasterer will warn you that skimming over old walls can crack. Someone who promises a perfect finish on a hundred-year-old wall without caveats is either inexperienced or not being straight with you.
Anyone who will plaster a damp wall without asking where the water is coming from is taking your money twice. It will blow within a year.
Everyone starts somewhere, but there should be something. Ask to see recent work.
Lime work is slow and skilled. A cheap lime quote is often cement with a bit of lime in it, and it will damage an old wall.
Run the back of your hand over it. It should feel smooth and flat, with no ridges, trowel lines or "snots", little lumps of dried plaster left on the surface. Look along the wall from the side with a light on it; that is where imperfections show.
Corners should be crisp and straight. The line where the wall meets the ceiling should be clean. There should be no plaster splattered on the skirting, the floor or the sockets, and no lumps left where the skirting is going back on.
And they should have cleaned up. Taking their mess with them is not a favour, it is part of the job.
Have a read of is it normal for new plaster to crack before you ring anyone. Some cracking genuinely is normal, and you do not want to accuse someone of a bad job when the plaster is just doing what plaster does.
But if it sounds hollow when you tap it, it is not normal, and you are entitled to have it put right.
The ones we get asked most.
Ask whether plastering is their main trade, how they will control suction on the wall, how many coats they are applying, whether they will use angle beads on external corners, how they will treat plasterboard joints, and whether they have worked on your type of wall before. The answers reveal more than the price does.
Warning signs include a quote that is just a figure with no detail of what is included, a demand for a large deposit before starting, no mention of the risks of skimming over old walls, a willingness to plaster over damp without asking where the water is coming from, no reviews or photos of previous work, and an unusually cheap quote for lime work.
Run the back of your hand over the surface. It should feel smooth and flat with no ridges, trowel lines or lumps. Look along the wall from the side with a light on, which is where imperfections show. Corners should be crisp, the ceiling line clean, and there should be no plaster splashed on skirting, floors or sockets.
A skim finish is two coats of finishing plaster. A single thin coat is a common cause of crazing and cracking. If the wall has been taken back to brick or blockwork, it needs a backing coat such as bonding or hardwall before the finish coats go on.
Some general builders plaster to a high standard, but many do not. A plasterer who does the work every day will typically give a better finish than a builder who plasters occasionally. It is a reasonable question to ask directly.
Send a photo on WhatsApp. We'll tell you straight, even if the answer is that there's nothing wrong.