Recommendations on best way to clean grooved decking of dirt, grease and heavy wear and tear markings and discolouration prior to treating with an oil or varnish. Do not want to change from existing natural colour if possible is there a clear matt product on the market either a brush varnish or an oil based wax. Views on varnish as opposed to oil.
Just use a power washer. If this doesn't work you can buy a decking restorer which removes any varnish etc and restores it back to its original state. I have seen restorers by firms like cupinol etc probably be able to get them at stores like b&q