Interior doors take a quiet battering in a small home. They are opened with elbows, propped with feet and wiped with whatever cloth is to hand. After a few years, that painted finish starts to look grey, scuffed and tired, and the whole hallway or landing feels duller as a result. Replacing them is rarely worth the money or the disruption, especially when standard sizes and old door frames can make a like-for-like swap surprisingly awkward. Repainting is one of the most cost-effective jobs you can do, and it is very much within reach of a careful beginner.

Why repainting is worth the effort

A new internal door can cost anywhere between £40 and £150, plus hinges, handles and the time spent trimming an ill-fitting frame. Repainting an existing door costs a fraction of that and keeps the character of a period property intact. In a small home, doors occupy a surprising amount of visual space. A hallway might contain four or five of them, so freshening the paint has an impact far beyond one door.

The trick is to treat the job as a proper decorating task rather than a quick wipe-over. Preparation and thin coats are what separate a smooth, hard-wearing finish from a streaky one that chips within months.

Prepare the surface properly

Paint will not hide a poor surface; it will simply make every bump more obvious. Start by removing the door from its hinges if you can, then lay it flat on trestles or a pair of sturdy chairs. Working flat stops runs from forming and makes the whole process quicker. Keep the screws in a labelled pot or thread them back through the hinge plate so they don't go missing.

• Wash the door with a sugar soap solution to remove grease, fingerprints and cooking residue, then rinse and let it dry.
• Sand the surface lightly with medium-grade abrasive paper, around 120 grit, to key the old paint. Finish with 180 grit for a smoother base.
• Fill any dents, splits or old screw holes with a two-part wood filler, then sand flush once cured.
• Scrape away any flaking or blistered paint back to a sound edge, and feather the edges with sandpaper.
• Spot-prime bare timber, and always seal knots with a knotting solution to stop resin bleeding through.

If the existing paint is very glossy, a light sand is essential. Modern water-based trim paints struggle to grip a slick alkyd surface, and you will see peeling within a season if you skip this step.

Choosing a durable paint

For doors, look for a hard-wearing trim paint rather than a wall emulsion. Water-based satin or eggshell is the practical modern choice: it dries quickly, has low odour, cleans up with warm water, and stays flexible enough to cope with a door slamming shut a hundred times a week. Traditional solvent-based gloss gives a tough, glossy finish and is very hard-wearing, but it yellows over time in dark hallways and takes much longer to dry.

Finish is a matter of taste and architecture. Gloss suits period panelled doors and bounces light around a narrow corridor. Satin or eggshell looks more contemporary and hides small imperfections better, which is useful on older doors that have seen a few decades of knocks. Buy a small tin of a decent brand rather than the cheapest available; the difference in coverage and durability is significant.

You will need a 4-inch foam or microfibre roller for flat sections, a good 1.5-inch synthetic brush for cutting in, a smaller brush for detailed mouldings, fine sandpaper, a tack cloth and low-tack masking tape if you are painting around glass.

Work in thin coats

Two thin coats will always beat one thick coat. Thick paint sags, dries unevenly and shows brush marks. Load your brush lightly and lay off in the direction of the grain or, on a flat door, in long vertical strokes.

Paint in a sensible order: start with the mouldings and panel edges, then fill in the flat panels, and finish with the stiles and rails around the outside. On a traditional four-panel door, work top panel first, then down, so that any drips fall onto unfinished areas you can tidy later. Keep a rag handy for the inevitable run along an edge.

• Allow the manufacturer's recommended drying time between coats, and longer in cold or humid weather.
• Sand very lightly between coats with 320-grit paper to remove nibs, then wipe with a tack cloth.
• Paint the top and bottom edges of the door as well; they are prime spots for moisture to creep in.
• Leave the final coat to harden for at least 24 hours before refitting, and a week before wiping the door down.

Handling hardware, glass and awkward spots

Mask around glazed panels with low-tack tape and remove it while the paint is still slightly soft, pulling it away at an angle. A sharp blade run gently along the tape edge will give a crisp line. Remove handles, latches and letterboxes where possible; painting around them never looks right and the paint will crack as soon as the handle moves.

If the door will not come off its hinges, wedge it open with a folded cloth at each end and paint one side, then the other, allowing longer drying times. It is slower, but perfectly workable.

Living with the result

A freshly painted door lifts a whole room, and in a small home that lift is felt immediately. Once the paint has cured, wipe marks with a damp cloth rather than an abrasive cleaner, and touch in any chips as soon as you notice them. Fit a felt or rubber door stop to protect the edge from handles and furniture, and consider soft-close hinges if the doors get a lot of traffic.

Set aside a weekend for two doors, buy a decent brush and don't rush the drying times. The finish you get from careful preparation and patient, thin coats will comfortably outlast a rushed job, and it costs a fraction of replacing tired doors with new ones.