When cleaning wood and similar materials, most cleaning techniques involve a form of air blasting.
By using specifically designed units that blast different types of grit at the material to clean in question, and altering the pressure and amount of ‘grit’ so to not damage any delicate materials.
Grits can vary from very soft, which could be baking powder used for cleaning window frames without inflicting damage on the glass, to harder grits like fine glass grit which would be used on timber.
Some methods use water for cleaning, some manufacturers claiming it cuts problems with dust, which it does, but fine grit and material being removed would easily be ingrained in the substrate and would be almost impossible to remove afterwards.
Timber and timber decking should be brushed to remove any dirt, debris or leaves, then proceed onto a pressure washer and then allow to dry for one or two days.
Once your timber has completely dried, apply a varnish or timber protector and allow to dry also.