Preparing your woodwork
If your woodwork is bare, you should consider treating it with a knotting solution first. This helps to seal the wood and prevents discolouration. Lightly coat the wood with your solution three times, waiting half an hour between each coat to allow the wood to dry. Once the final coat has dried, you should lightly sand the wood and also apply a coat of primer before painting.
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For painted wood, first lightly sand the woodwork to remove the gloss from the surface. This creates a texture to which the paint can adhere. If your door is old and you believe it may have been painted with lead paint, you should always consult a painter and decorator on how to remove the paint.
Next, wipe the woodwork down with a damp sponge to remove any dust and dirt. Avoid soaking the wood with the water, and give it time to dry after it is clean.
Painting your woodwork
You are now ready to paint your woodwork. Thinly apply your undercoat to the wood, working with the grain of the wood. If your wood was bare, you should apply a second coat once dry - otherwise, one coat will do.
Finally you should apply your topcoat. Again, apply this thinly, and work with the grain. Your paint will look better and last longer if you apply a number of thin coats, rather than fewer thick ones. One coat may be enough, but always allow to dry before you add any further coats.