Finishing Outdoor Wood Furniture  

Some Facts, Cautions and Instructions

for Finishing Outdoor Wood Furniture

This is the finish to use if you want a finish that is easy to apply, that will last a few years and that is easy to repair or refinish.  Finishing with Spar Varnish provides a durable, but flexible, finish.

A true Marine Spar Varnish, no matter what the brand, is made from tung oil and phenolic resin, two materials that have a natural immunity to UV light.  However, use a brand that has UV blockers or absorbers also, to protect the wood from fading.

Spar Varnish Characteristics:

• Durability:  Spar Varnish has very good water, solvent, heat, and stain resistance and also has fair scratch resistance.
• The formulation is made to be flexible enough to tolerate wood's movement throughout the year.
• (Spar Urethane mixtures are more likely to peel or delaminate than true Spar Varnish, although newer formulas may be less likely to peel.)
•  McCloskey and Varathane offer a true Spar Varnish, as do many companies whose products are sold in marine supply outlets.
• The Tung Oil in Spar Varnish is a drying oil that polymerizes in the presence of oxygen to a solid.
• Polymerization - A chemical reaction in which 2 or more small molecules combine to form larger molecules that contain repeating structural units of the original molecules.  There are numerous processes to acomplish polymerization.

• Marine Spar Varnish can be applied over previously oiled or stained surfaces without a problem.  In fact, you might try, on an inconspicuous area, applying a couple coats of good quality teak oil.  After the teak oil is completely dry, begin the Marine Spar Varnish applications.

Maintaining a Marine Spar Varnish Finish:

Mildew can grow on Spar Varnish but is easily washed off  with water and a small amount of household bleach.
Never use steel wool for any purpose when working with outdoor furniture as small pieces that flake off may be difficult to remove and will cause rust marks.

Safety Precautions:

• Be careful to work in a well ventilated work space.

•  Dispose of rags, pads and leftover product properly so as not to create a hazard to your health or to allow a fire to start.  Lay rags out in a single layer to allow air flow to hasten drying and dissipate heat.  After about 24 hours, they will be stiff and the oil will have cured.  Or put any rags, towels or finishing pads in water in a metal container with a tight lid. 

• Thoroughly read safety, storage, and disposal information on the can label.

Buy the Finishing Kit

Outdoor Furniture Finishing Kit Includes:

Supplies that you will need to have on-hand:

Can opener or flat-head screwdriver to open spar-varnish can.
Medium, Fine or Extra-Fine sandpaper for initial smoothing, depending on the surface quality of the item being finished.

Application Process:

Work in a protected space with good ventilation and good light, preferably natural light.  Check your work frequently from different angles to be sure the application is even.
Check all surfaces to be sure that they have the smoothness suitable for your purposes.  Use either medium to fine sandpaper or medium to fine finishing pads to get the smooth surface that you desire.  Do not use steel wool.
Read the directions on the can and carefully adhere to all safety precautions.
Open the Spar Varnish can & stir thoroughly but without creating bubbles until all settled material is incorporated.  This may not be a quick process but it is necessary.  Do not shake, this will create bubbles in the product.  Stir frequently, especially before pouring into the disposable container.  Satin Marine Spar Varnish will take longer to mix due to the "flatting agents" used that differentiat it from a gloss finish.
Pour some of the Spar Varnish into a disposable container.  I sometimes use the plastic measurer that comes in laundry soap to scoop some of the product and put it into the disposable container.
With the disposable gloves on, dip the fine, gray Finishing Pad into the Spar Varnish in
the disposable container.
Scrub some of the Spar Varnish onto a section of the furniture  Always work with the grain of the wood, not across the grain.
Wipe it all off before it gets tacky using lint free paper shop towels, with the towel flat and working with the grain of the wood.  This will require that you work in sections so that the finish does not get tacky before you are ready to wipe with the towels.  If it does get tacky, scrub again with a small amount of spar varnish on the finishing pad until smooth, then use more spar varnish,  scrub it in some more and again wipe with a paper shop towel.
To avoid "lap" marks, try to end a section at an edge
Move to the next section and continue the process.
Be sure to cover all sides and pay special attention to cut ends.  Don't leave even a small area where moisture can enter or get under the finish.  You may want to finish the underside areas first and later do the upper areas.  The underside is also a good place to get in a little practice and help you decide how large an area you can work at one time without any of the area getting tacky.  Don't forget to cover ends, between slats, and other small areas.  It is important to cover all areas to prevent moisture from getting under the finish
Let the piece sit overnight at room temperature, or warmer.  Dry times vary depending on temperature and humidity.  Check for tackiness before applying another coat.  If there is any tackiness, extend the dry time.
Repeat the process at least 3 times if the piece will be somewhat protected from the elements. Repeating the process at least 5 times will give you a much more durable finish that will withstand the elements much better and is well worth the initial effort.  Use a new finishing pad for each application.  Since you will be scrubbing with the finishing pad as you apply each coat, sanding between coats is not necessary.
 

Maintenance:

 The result will be a thin coat of Spar Varnish with no brush marks, no dust and no drips or
 runs. If it starts to show wear, clean it, scuff it lightly with 400 grit sandpaper, vacuum, then use the microfiber reusable, washable cloth to remove any sanding dust and repeat the original process.

Information about Teak Oil and Danish Oil:

Most Danish Oil is generally not appropriate for outdoor use although Waterlox Marine and Watco Exterior are appropriate, when several coats are applied to build up some thickness. However, these are still inferior to Marine Spar Varnish for application to outdoor furniture.  
Linseed Oil, in many Teak or Danish Oil products, tends to yellow with age; also reacts with water and causes black blotches.
Danish Oil Durability: poor water, scratch, and stain resistance; moderate solvent and heat resistance.
Linseed Oil and Tung Oil Durability: poor water, scratch and stain resistance; moderate solvent and heat resistance.
Teak Oil traps dirt and darkens with age.  This darkening is especially noticeable on light-colored woods.  Traditional teak oil is an organic oil that encourages the development of mold and mildew.  

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