There are two very easy finishes to apply to outdoor wooden furniture such as swings and picnic tables. 

 Steps to an excellent finish are:

Sand to 100 Grit

Lightly sand the bare wood with 100-grit sandpaper.

Be sure to “break” sharp edges.  “Breaking” a sharp edge means to lightly roll or curve the edge so it is not sharp.  This helps the finish adhere to the edge and not open up or be easily damaged when the edge comes in contact with another object.

Remove Dust

Blow away any residual saw dust from the project, and use a tack cloth.

For the best possible finish, it is absolutely necessary to remove all traces of sanding dust from the surface. Tack cloths do the job, picking up every bit of dust from your project and giving you a perfectly clean surface that’s ready to finish.

Start Upside Down

Whether spraying or brushing the project, start with the item upside down.  This way, when the item is turned over to the upright position for the final finish, if the finish does overspray or run, the blemish will be on the back side where it will not be seen.

Apply Finish

Use Marine Varnish or Outdoor Oil.

Marine Varnish is a high solid finish was designed for marine and exterior surfaces such as boats, outdoor furniture, doors or any exterior surface where a strong water resistant finish is desired. It contains Ultraviolet Light Absorbers, which offer excellent protection from the sun. Formulated to protect against the harshest salt water and marine environments, Marine Varnish will provide long lasting protection. Marine Varnish is typically available in Satin or Gloss. Resanding will be necessary when the finish becomes worn and needs to be reapplied in the future.

Outdoor Oil is specially formulated for outdoor wood projects, from log homes to decks to furniture. It contains both oil and resin, along with UV inhibitors, heat stabilizers and mildew inhibitors that make it ideal for all exterior weather conditions. It may be used over other brands of exterior oil stain or exterior clear oil finishes for additional protection. When the finish becomes worn, all that is needed is to clean the surface and reapply outdoor oil.  No resanding is needed.

These top options make for a very good looking result and provide very good, easy to apply protection from outdoor weather.