A coat of finish will give your door the protection it needs against unwanted moisture. This is especially important in external doors, which must face constant changes in humidity, temperature and pressure over their lifetimes. If water has managed to get into the fibres of the wood, it’ll exacerbate warping effects and cause your door to change shape more quickly. It might also rot the wood – which is disastrous, and will probably necessitate the door being replaced. As such, it’s worth waiting for a very dry day before doing this job – as if the door gets wet before you’ve applied the paint, you’ll be unable to get started. Before applying a new coat of paint, you’ll need to remove the old one. But first, we’ll want to prepare the door for painting. Lay down an old bedsheet or some newspaper. Remove the furniture from the door – including letterboxes, knockers, handles and locks. Next, remove the paint using paint stripper. If a little bit of paint remains, don’t worry – you’re going to be sanding the entire door next with light sandpaper to achieve a smooth finish. Run a damp cloth over the entire door to remove any loose pieces of grit or dust, and let the door thoroughly dry; you’ll then be ready to get started with painting it. You’ll need to apply several coats of paint to achieve the desired finish, letting each properly dry before moving onto the next. The first of these should be a coat of primer, which is usually white in order to help subsequent layers show up as the right colour. Once that’s done, you’ll want to apply a coat or two of gloss – it’s better to apply several very thin layers than a single thick layer, as the latter will be far more prone to dripping. Once the topmost coat is dry and you’re happy with the way the door looks, you’ll be able to reattach your hardware. If you’re setting a day aside to paint the door, get started as early in the morning as possible – each layer of paint will dry far more quickly in the middle of the day, and you won’t want to leave your back door unlocked when you retire for the evening!