Preparation Is Where the Finish Is Won

Paint and wallpaper are unforgiving things. They will not hide a dint, a hairline crack or a patch of shiny silk paint that has never been keyed — they will simply draw attention to it. Ask any decorator which part of the job takes the longest and they will tell you it is the preparation, not the topcoat. Get the walls right and the finish looks flat, even and professional for a decade. Rush it and you will be back in the same room in two years, scraping and cursing.

The good news is that none of this is difficult. It is just methodical. Set aside a full day for preparation on an average room, and you will be surprised how much of a difference it makes.

Gather Your Kit Before You Start

Half the battle is having the right materials to hand so you are not stopping every ten minutes. For a typical room you will want:

• Fillers: a powder-based filler for deep holes, a lightweight ready-mixed filler for fine surface dints, and a flexible decorator's caulk for gaps where two surfaces meet and move slightly.
• Abrasives: 120-grit for shaping filler, 180-grit for general keying, and 240-grit for a final smooth before priming. A sanding block stops you digging hollows into the wall.
• Cleaning kit: sugar soap, a bucket, and two sponges — one for washing, one for rinsing with clean water.
• A filling knife with a flexible blade, plus a smaller one for tight corners.
• Dust sheets, masking tape, a dust mask, and a vacuum with a brush attachment for the final clean-down.
• Primer suited to your surface, and knotting solution if you are painting bare timber.

Fill Every Hole, Crack and Dint

Work in good light and ideally with a lamp held at a low angle to the wall — side-lighting reveals every imperfection that flat daylight hides. Fill screw holes and small dints with ready-mixed filler, pressing it in with the knife and drawing it flush in one smooth stroke. Do not over-work it; the more you fiddle, the rougher it dries.

For deeper holes, use a powder filler mixed to a thick paste and build it up in layers. Anything more than about 5mm deep is likely to shrink and crack if you try to do it in one go, so let each layer set firm before adding the next. Leave the final layer very slightly proud of the surface, then sand it back flat once fully cured — usually the next day, not twenty minutes later. A common mistake is sanding filler while it is still soft, which tears it and leaves a dip.

Where walls meet ceilings, and where skirting meets plaster, a bead of decorator's caulk is better than filler. Run a thin bead, smooth it with a damp finger, and let it cure. It stays slightly flexible, so it will not split as the building moves.

Key Gloss, Silk and Other Shiny Surfaces

New paint will not grip to a glossy surface. If your walls are currently covered in silk emulsion, gloss or eggshell, you have two sensible options: key the surface or strip it. Keying is almost always quicker and perfectly sound.

Start by washing the walls with sugar soap to remove grease, nicotine and general grime, then rinse with clean water and let them dry completely. Next, sand the whole surface lightly with 180-grit paper — the aim is not to remove the paint but to scratch through the shine so it feels dull and slightly rough to the touch. Pay attention to corners, the tops of walls and anywhere hands have touched. Wipe or vacuum off the dust, then apply an adhesion primer. A dedicated gripping primer over glossy paint saves a lot of worry and gives the new finish something to bite into.

Prime and Seal Before You Decorate

Priming is not optional, and it is not the same as painting. It seals the surface, evens out absorbency and stops stains bleeding through.

• Bare or freshly skimmed plaster needs a mist coat: emulsion thinned with water, typically around four parts paint to one part water. This soaks in and gives the topcoats something to hold. Make sure the plaster is genuinely dry first — pale, chalky and dry to the touch, which can take several weeks on a new skim.
• Filled patches soak up paint faster than the surrounding wall and will show as dull spots unless you spot-prime them first.
• Bare timber and knots need a primer, and knots need knotting solution or they will weep brown resin through the paint.
• Water stains, smoke marks and ink need a stain-blocking primer. Standard emulsion will let them creep back within weeks.

The Final Check Before the First Coat

Once everything is filled, sanded, washed and primed, give the room a proper clean-down. Vacuum the walls, wipe the skirting and settle the dust. Then run a bare hand across the surface — your fingertips will find what your eyes miss.

Check that every filled area is truly dry and flat, that no filler has shrunk back into its hole, and that the edges of your filled patches are feathered rather than ridged. Now is the moment to catch a missed crack, not after the second coat. When the walls are smooth, dry and dust-free, you can paint or paper with confidence, knowing the finish will look as good in five years as it does on the day you finish.