Decking oils feed the timber, seal and enhance the natural beauty of your decking while providing a tread fast surface. They are usually applied to horizontal surfaces, but can also be used for any type of exterior wood work. There are few good decking oils around today, there are also lots of rubbish cheap decking oils which will peel and flake and require re-applying every six months or so.
Note-- Clear decking oils if exposed to direct sun light will NOT give long term protection if used as a stand alone coating.
It is highly advisable on all new decking timbers to give it a good scrub/clean first with white spirit and allow to dry before the application of decking stain/oil, this process will remove any contaminants on the surface. These contaminants attach to the surface during the manufacturing, storage, transportation and installation process and will cause your new applied coating to fail (peel and flake) if not removed. Your new decking may be new to you but the timbers have been around the block a few times before you had it installed and will be contaminated.
A light sanding with 180 grit sand paper after cleaning will open up the grain of the timber and greatly help with better penetration of the coating.
On all new oily and exotic timbers allow 3-4 months exposure to the weather then clean as above before applying the decking oil.
Most water based decking products are not very successful on oily timbers.