Clear wood finishes that protect outdoor surfaces with direct sun exposure face a very difficult task. The regular and chronic UV exposure and expansion and contraction of wood surfaces as the seasons and weather change, create a very difficult environment for coatings. Waterlox does offer the MARINE and PURE Tung Oil product lines that can work on exterior projects. For decks/porches specifically, please refer to our Waterlox on Decks and Porches guide. Also be aware of any mold or mildew situations on exterior projects and refer to our mold and mildew guide for more information.
Waterlox MARINE finishes are a traditional spar varnish (not a spar urethane) made from tung oil. These form clear protective, yet elastic, films that are designed to be in a high UV exposure environment. The finishes provide the same excellent protection from salt/fresh water as all our finishes, but they have the added benefit of UV resistance.
Spar Varnish Explained
Our MARINE finishes are traditional spar varnishes made with tung oil. The important aspect of spar varnishes is that they have very good flexibility and they do not become brittle with time. The term “spar varnish” comes about as a finish used on the wooden spars (masts, booms, gaffs, etc.) on sail boats to protect them from the sun and the elements. These spars can bend and flex significantly, so any coating will need to bend without cracking or splitting. Also, when wood is in a non-climate controlled environment (outside) it can expand and contract significantly as the humidity and seasons change and the coating needs to move with the wood. If the finish is too rigid, the coating can crack when the wood moves and then eventually start to chip or peel away leaving your surface unprotected.
Many clear wood exterior products will have great flexibility and protection when they are fresh. The problem is that UV light tends to over cure many finishes. As the coatings continue to cure, they lose their flexibility and start to fail. They then need to be removed and reapplied.
Waterlox MARINE finishes are specially formulated to not become brittle even after many years of exposure. If completely left unattended or unmaintained, they will eventually fail, but they will give ample warning when they look dull and faded.
Lifespan and Maintenance of MARINE Finishes
The lifespan of the MARINE finishes is completely dependent on the amount of sun exposure that the surface will encounter. Full, all-day exposure will be harshest and will require more frequent maintenance. Also, horizontal surfaces will usually age faster than vertical surfaces, as any water droplets can act like magnifying glasses on the surface. Fully exposed surfaces may need reapplication yearly (i.e. a boat deck that’s stored outside) where a bench under a large tree may last 7-10 years or more. When the finish starts to look dull/faded, that is a signal for recoating.
A light cleaning and a fresh coat will restore the coating and the protection. See the refreshing and recoating a Waterlox finished surface guide for more information. We have noticed that many projects tend to have a “settle in” period where it acclimates to the environment and the seasons. You may see areas that fail or wear out faster than others. In our experience, most reapplications tend to last longer than the initial application as the difficult spots are identified and resealed.
DO NOT USE MARINE FINISH INDOORS
Many people assume that “Marine” means extra waterproof and therefore they should use it around the sink or on bathroom vanities. The truth is that they are equally waterproof to our interior finishes, but the MARINE finishes are designed to be flexible and designed to be exposed to UV. The UV helps to properly cure the finishes and without it, they can stay rather soft, making them a poor choice for floors, vanities and countertops.
The only instance where it would be OK (not ideal, but OK) to use the MARINE products indoors would be on the interior of a door to keep the finish consistent on both sides if desired. It will stay softer, but the demands on a door are typically much lower than most surfaces.
PURE Tung Oil
PURE Tung Oil is very versatile and works well on interior and exterior projects. Its initial reported usage was to seal wood on Chinese sailing vessels over 2000 years ago. It is a pure oil coating, so it will never crack, chip or peel, but it will simply wear away and need more regular replenishment. It is not a natural mold or fungicide (nor does it support it), so you may want to pretreat any projects (see the mold and mildew guide) to prevent any potential issues. The tung oil will saturate the wood surface and requires a few applications to get it well saturated on raw wood. The result will be a very matte, “unfinished” look where there is no real coating left on the surface, however it will easily repel water. See our PURE Tung Oil on Decks guides for more information on how to use the products.
Lifespan and Maintenance of Pure Tung OilA PURE Tung Oil finish will never crack, chip or peel because there is no real coating left on the surface. The oil will slowly wear away or be “burned off” by the sun. When the wood starts to look dry or water no longer beads up on the surface, clean the surface well and apply more tung oil to resaturate the surface. There will usually be some touch up required yearly or even more often in particularly harsh environments. Also, the initial application will probably wear off a little faster as the wood settles into its environment.
Outdoor Projects with NO Direct Sunlight
Both the MARINE Finishes and the PURE Tung Oil will also work on surfaces with no direct sunlight. You can also use our TRUETONE and ORIGINAL products as they have excellent flexibility for non-climate controlled surfaces, however, they do not have proper UV resistance.This would work well for porch ceilings, wooden furniture/equipment that is stored indoors, etc.