How to Fill and Paint Interior Woodwork Neatly

Why Preparation Decides the Finish

Paint is unforgiving. It magnifies every dent, every ridge of old paint, every hairline gap where the skirting meets the wall. If you want interior woodwork that looks genuinely professional — sharp edges, a flat sheen, no visible brush marks — you have to spend far longer preparing than painting. A good rule of thumb is four parts preparation to one part paint.

The job breaks down into three stages: filling, sanding and priming. Get those right on skirting boards, door frames, architraves and window sills, and the topcoats will almost apply themselves.

Gather the Right Kit Before You Start

Nothing slows a job like hunting for a missing scraper with a brush in your hand. Set everything out on a dust sheet first.

• Fillers: a lightweight interior filler for fine cracks and nail holes, a two-part epoxy filler for deep or structural gaps, and a decorator's caulk for the joint where wood meets plaster.
• Abrasives: 120 grit for shaping filler, 180 grit for general smoothing, 240 grit for keying between coats, plus a sanding block and a flexible foam pad for mouldings.
• Primer: a stain-blocking or knotting primer for bare knots, and a wood primer or combined primer-undercoat for bare timber.
• Brushes: a 50mm synthetic brush for cutting in, a smaller 25mm brush for mouldings, and a fine roller for flat sills if you prefer.
• Others: a filling knife (not a putty knife — you want a flexible blade), a scraper, masking tape, a damp cloth, and a vacuum with a brush attachment.

Repair and Fill in the Right Order

Work from the deepest defects outwards. Start by scraping back any flaking paint with a stiff scraper, then sand the edges feathered so you cannot feel the step. Fill deep holes, then medium cracks, then fine ones.

Push lightweight filler into the gap with the knife at a shallow angle, then draw it across in one smooth stroke. Slightly overfill — filler shrinks as it dries, and a proud surface sands back level while a hollow one does not. Leave it proud by a millimetre or so, no more.

For knots in bare timber, dab on knotting solution before anything else; skip it and the resin will bleed through every coat of paint you apply. For the gap between skirting and wall, use caulk rather than filler. It stays slightly flexible as the building moves, and it takes paint beautifully. Run a thin bead, then smooth it with a damp finger or a caulking tool for a neat concave line.

Sanding: The Step Most People Rush

Once the filler is dry — usually an hour for lightweight, overnight for two-part — sand it flush with 120 grit, then refine with 180. Wrap the paper around a block for flat runs and use a foam pad for curves and beading. You should not be able to feel where the filler ends.

Check your work by running your fingertips along the woodwork with your eyes closed. Your hands will find faults your eyes miss. Then wipe everything down with a damp cloth and vacuum the room. Dust left on the surface will show up as grit in the finish, and it will ruin your brush in minutes.

Prime for an Even Base

Bare timber drinks paint unevenly, so always prime. A primer-undercoat seals the grain, gives the topcoat something to grip, and stops shiny patches appearing through the finish. Brush it on thinly and let it dry fully — usually four hours for water-based products.

If you are painting over existing gloss, do not skip this stage either. A light sanding with 180 grit followed by a bonding primer creates the key that stops new paint peeling off in sheets. Gloss is a notoriously slippery surface, and paint will simply slide off it if you have not broken the shine.

Painting Neatly, Coat by Coat

Mask the wall, the floor and the glass before you open a tin. Press the tape down firmly and remove it while the final coat is still just tacky — pulling it off a fully cured edge can tear the paint line.

Apply two thin coats rather than one thick one. Thin coats level out, dry evenly and leave far fewer brush marks. Load your brush about a third of the way up the bristles, tap off the excess, and lay the paint on in long, flowing strokes following the grain.

For cutting in along walls and floors, work in sections of about a metre. Paint a line along the edge first, then fill in the flat areas and blend the two together while both are wet — this is what removes visible joins. Keep a damp cloth to hand for the inevitable slip; wiping immediately saves a lot of swearing later.

Leave the room alone until the paint has fully cured, not just dried to the touch. That takes a few days for most water-based eggshells, and it is when the finish hardens into something genuinely durable. Sand lightly with 240 grit between coats, dust off, and your woodwork will look like it was done by someone who does this for a living.