Ask a decorator what separates a good finish from a disappointing one and almost none of them will start with paint. They will talk about the days before the first coat: the filling, the sanding, the priming, the patient business of making a wall flat and stable enough to take colour evenly. It is unglamorous work, it produces no dramatic before-and-after photograph on its own, and it is the single biggest reason two rooms painted with the same tin can look completely different a month later.
This matters more in London and Surrey homes than most people expect. A Victorian terrace in Fulham, a 1930s semi in New Malden and a newly extended house in Esher all present different problems — old lime plaster, decades of layered paint, hairline settlement cracks, fresh plasterboard that has never been sealed. Paint does not hide any of that. Modern finishes, particularly the flatter matt emulsions people now choose for walls, are unforgiving: they sit tight to the surface and show every ripple, every proud filler patch and every missed sanding mark once light rakes across them.
What preparation actually involves
Preparation is not one job but a sequence, and each stage exists because of a specific failure it prevents. Skipping any of them shifts the problem to the finish coat, where it becomes visible and expensive to correct.
Protection and stripping back
Before anything else, the room is cleared and covered — floors, carpets, fitted furniture, radiators, ironmongery. Then the surfaces are assessed properly, which usually means removing what cannot be painted over: flaking paint, blown plaster, tired wallpaper, old sealant along skirtings, and any coating that has lost its grip on the substrate. Painting over a failing layer simply means the new paint fails at the same depth, on the same schedule, only now with your money on top of it.
Making good and filling
Filling is where judgement shows. Different defects need different materials: a fine surface filler for shallow scuffs and nail holes, a deeper two-part or setting filler for chunks out of a corner, flexible caulk where two different materials meet and will move against each other, and specific crack repair — sometimes with tape or scrim — where a hairline has opened up along a plasterboard joint or above a doorway. Overfilling and then flattening back is almost always better than underfilling and hoping the paint bridges the gap.
Sanding
Sanding does two things at once: it levels the filler into the surrounding wall so no repair can be felt with a flat palm, and it gives previously painted surfaces enough key for the next coat to bond to. Woodwork in particular needs de-nibbing between coats, because dust and brush debris settle in wet paint and set hard. Good sanding is progressive — a coarser grit to remove material, a finer one to remove the marks the coarser grit left. On any decent-sized job it is done with dust extraction, both for the finish and for the household.
Priming and sealing
Primer is not a cheaper first coat of paint; it does a different job. New plaster needs a mist coat so it does not drink the first proper coat unevenly. Bare or resinous timber needs a primer that will block tannins and knots from bleeding through a white finish months later. Water stains, nicotine and old smoke damage need a stain-blocking product, because emulsion will simply carry the discolouration to the surface, coat after coat. Repaired patches also need spot-priming — otherwise the filler absorbs differently from the wall around it and you get 'flashing', where every repair shows as a dull shadow through the finish.
The wall defects worth dealing with properly
Some problems are cosmetic and some are symptoms. A competent decorator should tell you which is which before quoting, because the second kind will come back through new paint.
- Hairline cracks that follow plasterboard joints or run diagonally from door and window corners — usually movement, and they need a flexible repair rather than rigid filler.
- Nail pops and screw heads pushing through skim on stud walls, which have to be set back below the surface before filling.
- Blown or hollow plaster that sounds drummy when tapped — it has lost its bond and needs cutting out, not filling.
- Peeling in bathrooms, kitchens and around windows, which often points to condensation or moisture rather than bad paint.
- Damp patches, tide marks and salting, which must be traced to a source and resolved before decoration; paint is not a damp cure.
- Previous poor filling: proud patches, sanding halos and roller texture from an earlier repaint, all of which telegraph through a new flat finish.
- Silicone or grease contamination near cookers and splashbacks, which stops paint keying unless degreased first.
Why the preparation time is not padding
Clients occasionally ask why two or three days of a schedule go by before any colour appears on the walls. The honest answer is that this is the part of the work that cannot be recovered later. A finish coat takes hours; the flatness it sits on takes days, and no amount of extra paint compensates for a surface that was not right. Fillers also need time — proper drying before sanding, then dust removal, then priming, then sometimes a second round of filling once a mist or primer coat has revealed defects that were invisible on bare plaster. That is not slow working, it is the point at which faults are cheapest to fix.
There is a durability argument too. Paint bonded to a sound, keyed, sealed surface behaves well: it resists knocks in a hallway, it takes cleaning in a kitchen, and it does not peel in sheets when a picture hook comes out. Paint sitting on dust, gloss or a failing layer beneath it does none of those things, however good the product on the tin.
What good preparation looks like when you walk in
You do not need to be a decorator to judge preparation. A few things are visible to anyone who looks at the room at the end of the day.
- Everything that is not being painted is covered or removed, and the covering is still in place at the end of the day rather than kicked into a corner.
- Repairs cannot be felt when you run a hand across the wall, and they are not visible as raised or dull patches once primed.
- Edges are crisp: caulk lines along skirtings and architraves are neat and consistent, not smeared into the wall.
- Woodwork feels smooth rather than gritty, with no runs, sags or brush debris set into the surface.
- Dust is controlled during the work and cleared at the end, not left to settle back onto wet paint the following morning.
- The decorator can explain why a particular filler, primer or repair method was chosen for that specific surface.
How preparation shapes a quotation
Because preparation is the variable part of decorating, it is also what makes two apparently similar rooms quite different jobs. The factors that genuinely change the scope are the condition of the existing surfaces, how much filling and stripping back is needed, the size and number of rooms, the materials and finish you choose, the complexity of the detail — panelling, cornice, spindles and sash windows all take longer than flat walls — and how easily we can access the work, including stairwells and high ceilings. Those are the things worth discussing on site, and they are exactly what we assess before putting anything in writing.
If you are weighing up redecorating a room or a whole house, the most useful next step is having someone look at the actual surfaces rather than describing them over the phone. You can see the standard of finish this preparation produces across our recent interior work, read how we sequence a full interior painting project from survey to handover, or request a free tailored quote and we will talk you through what your walls need before a brush goes anywhere near them.