We are often asked how to refurbish mouldy or slippery decks. First rule; take caution using a water blaster. To get technical a powerful water blaster can break down the molecular structure of the timber fibres leaving them damaged and frayed and this then promotes future growth of mould spores. We recommend you take your time water blasting and hold the water blaster nozzle about 500 mm above the deck. Then add treatment, mould removal products are readily available (Bunnings etc), the next day apply two coats of an 'oil based' deck oil or deck oil and stain (to add colour) and re-apply every one to two years, (or before you sell), It should only take 1 to 2 hours to apply deck oil/stain for an average size deck with $80 worth of product. Allow the deck oil/stain 1 to 2 days to fully dry depending on how porous the timber decking is, how thick you apply coats and the weather. Caution: many years ago I applied two very thick coats of Wattyl Blonde (white) deck oil to our deck, the decking timber was only a year old, it took 5 days to fully dry and I had to rope off the deck for during our 'open home'.