• A weathered oak door.Aged door handle on wooden entrance door image by fotosergio from Fotolia.com
  
  Oak is naturally a strong, hard and highly durable material that is resistant to the elements, fungi and insects. However, untreated oak doors, external or internal, will sooner or later succumb to the effects of moisture -- rain, humidity or condensation -- and should be treated with an appropriate stain, oil varnish, wax or paint before hanging, and at regular intervals, if they are to last a reasonable length of time.
  
  

Stain, Oil or Varnish

• An oak door may be treated with a stain, oil or varnish finish at the factory, but, depending on the type of finish applied, even these may require a further treatment within a few months and at regular intervals thereafter. Untreated oak doors should be sanded, if necessary, to ensure that they are completely smooth and thoroughly cleaned to remove handling marks, grime and wood particles, before treatment. Several coats of stain, oil -- such a Danish Oil, extracted from the tung tree or linseed plant -- or varnish should be applied to all surfaces of the door, including the top and bottom surfaces, to ensure that it is completely sealed.
  
  

Wax

• There are numerous wax-based products designed to nourish and protect unsealed internal and external oak doors on the market. Some of these are formulated to be water-repellent -- without containing harmful chemicals -- and are suitable for exterior use or interior use in rooms that are especially damp. Others, such as beeswax, protect oak doors against excessive dryness, while others, such as specialist liming wax, can be applied with steel wool -- after first opening the grain with a bronze hand brush -- to create special effects.
  
  

Paint

• Paint is, perhaps, the most straightforward treatment for oak doors. Once again, paint may be applied to an oak door at the factory, in which case no further initial treatment is required. Untreated oak doors for exterior use should be painted with a coat of primer, two coats of undercoat and two coats of exterior gloss paint, making sure to cover all surfaces of the door to prevent moisture entry. If you need to refinish an existing door that has been painted or finished in some other way, you may need to roughen the surface with sandpaper before applying primer and paint. You do not, necessarily, need to remove the existing finish in its entirety; you just need to create a surface that is rough enough for the new primer and paint to be applied effectively.