This article was inspired by a question from K Sanchez who writes: “What is the the difference between spar varnish and regular varnish?”
Why We Need Outdoor Formulations
Before we dig into the details, let’s talk about why we need a different varnish for outdoor applications. Any wood stored outside is going to be exposed to a wide range of temperatures and weather, as well as a good dose of damaging UV rays. These elements serve to break down the finish over time. Furthermore, changes in humidity cause the wood to expand and contract, and a standard indoor finish would simply crack and deteriorate under these conditions. Spar varnishes are typically designed to not only protect the wood, but also give it the flexibility and UV protection it needs to last for years. And the name “spar varnish” comes from the boating world, where the long wooden poles that support the sails are know as spars. So a spar varnish needs to be one that can withstand the rigorous conditions of seafaring life.
The Components
Nearly all modern varnish contains a few basic components: oil, resin, and a solvent. By modifying the types and amounts of these components, we can create a whole range of mixtures that vary in price and are specifically suited for either indoor or outdoor use. Fortunately for the inquisitive finisher, there are only so many ingredients that manufacturers have to choose from. And this makes it easier to see beyond the marketing jargon to deduce how a particular finish will behave. Here are the most common recipe ingredients:
Oils – Linseed Oil or Tung Oil
Resins – Alkyd, Phenolic, or Polyurethane
Solvents – Mineral Spirits, Naptha, or Paint Thinner
Oil to Resin Ratio
When a varnish is made, the ratio of oil to resin can have a dramatic effect on the way the varnish will behave. For instance, using a small amount of oil and a large amount of resin will produce a very hard but somewhat brittle finish. Obviously, this is not suitable for outdoor applications since we need an outdoor finish to be flexible. So what makes more sense is to create what is known as a “long-oil varnish”, that is, a formulation that contains a greater percentage of oil. The extra oil results in a softer, more flexible finish that will not crack when the wood expands and contracts.
Oil Types
The most common oil used to make varnish is linseed oil. Its lower cost makes it the most practical choice for both indoor and outdoor formulations. But many believe that tung oil is actually better for outdoor use. After all, a higher quality oil should equate to a higher quality varnish, and thus a higher price tag. As a result, many of the high-end marine varnishes will be made with tung oil instead of linseed oil.
Resin Types
Generally speaking, phenolic resins are best-suited for outdoor use. But that doesn’t mean every spar varnish is made with phenolic resins. Much like the situation with oils, the better product is also the most expensive. So you’ll find plenty of outdoor formulations using alkyd and urethane resins. A popular finish like Helmsman Spar Urethane contains urethane modified alkyd resins. A higher quality finish like Epifanes contains phenolic modified alkyd resins. There are many other brands of outdoor oil-based varnish, but the ingredients list is usually much more revealing than the words on the front of the can.
Sun Block For Wood
Most spar/marine varnishes will contain other important additives, such as UV blockers, that give the wood that extra bit of protection it needs in harsh conditions. UV light will not only damage the wood, but also the finish itself, eventually resulting in finish failure. So its a good idea to use a finish containing UV-blockers for any outdoor project.
Conclusion
Generally-speaking, my preferred outdoor varnish would be a long-oil varnish made with tung oil and at least some phenolic resins and UV inhibitors. And most times the brand I reach for is Epifanes.
If you’d like to learn a little more about how I apply varnish, check out this article: A Better Way to Apply Spar Urethane
If you want to learn more about my favorite finishing method, you should check out my DVD, A Simple Varnish Finish. My goal with the DVD was to demystify finishing by going over each and every step of the wiping varnish process. Even someone new to the world of finishing can create a show-stopping finish if they follow the methods outlined in the DVD. So check it out!
Recently, I painted two murals for the exterior wall of my employer’s courtyard. This will be exposed to harsh winter weather, hard winds and heat (being mounted on a metal-sided building). Because of this, I chose what I thought were the best-quality materials and paints for the job. I bought 3/4 inch marine-grade plyboard that won’t bend or peel or decompose over time. I put one coat of primer over it before painting the scenes with Sherwin Williams’ exterior latex paint (can’t remember the name of it but it’s very thick). Then, I put three thin coats of Helmsman Spar Varnish on it to protect it from the extreme weather conditions and sunlight. My questions are: did I use the right materials (I’m sure I did; but it’s my first outdoor murals) and can it be covered with a glass encasement without ruining the finish? (our maintenance man insists on it, but I don’t think it needs it).
Hi Gail. This is a bit outside my wheelhouse. I don’t typically work with paint and I have no idea about the glass encasement. I can’t see why glass would harm anything though. And since the finish is already on there, you’ll just have to see how it pans out. I don’t feel that Helmsman is the best varnish for the job, but it’s a little late to change it. :)
Getting Ready to put a Walk in shower All Ceder would like to Waterproof do You have and Hints
Marc,
I made a lovely bellrope recently. I used good old Man-O-War Spar Varnish to waterproof it and to UV protect the cotton rope.The next step is to add the decorative colors to it. Do you know what type of paint sticks best to spar varnish?
Thank you!
Honestly I don’t use paint much myself. But with a good primer, im sure just about any paint will adhere.
Hi there, We are installing Ikea butcher block countertops in our (heavily used) kitchen. We are planning on using an undermount sink. In addition, our kiddos have been known to “not see” and leave spills on counters, [floors, furniture, carpet, the dog, etc.] indefinitely. We will not be cutting on the countertops. We are considering using marine spar for durability and ease of maintenance. Do you see any issues with this? What product(s) would you recommend that require little to no maintenance and offer superior moisture protection? Thank you so very much! We certainly appreciate your expertise and recommendations.
Polyurethanes are a good way to go. Even something like Behlen’s Rock Hard Table Top Varnish is a good option. They should all repel moisture effectively. Of course long-standing spills can always cause issues, but that’s the drawback of wood countertops.
I am building a solid bodied guitar.
How does spar varnish rate in that application?
Thanks,
Mike
I know many folks who use varnish on their musical instruments, so it should do quite well. But I’d look into some luthier forums if you want a little more detailed information on instrument finishes.
Thank you for the info you provide on your website!
My problem: I refinished my Victorian interior woodwork with several coats of Ben Moore oil based sanding sealer. That is all I used and it looked great! See pics http://www.oldhouseguy.com/my_restoration . Now 15 years later the stain in the wood seems to be fading. I guess I should have applied a coat of varnish to protect it.
Sadly today you can’t buy real oil based varnish anymore and I don’t think I should use a Poly. It seems that the only oil based non-poly is Man-O-War Spar varnish. I currently use this on my front door and window sills and never thought of using it on millwork or furniture. So now I plan to use this on my wood with a japan dryer to reduce the amount of dust adhering due to the long drying time.
So – am I right so far? Please correct me if you have other ideas.
Additionally since the stain seems to be fading I would like to tint the varnish. The Benjamin Moore guy said I could bring in a small container for some universal stain in Burnt Sienna which I must mix up. Do you think this would work?
Your help is much appreciated!
Ken
no need to reply – project is finished and went well. Thanks for your help!
Good day. I’m getting ready to install my exterior siding (1×6 t&g pine) and want to leave the wood clear but protected. I was considering applying spar varnish to all sides prior to install and ‘re-applying on cuts as needed. Do you concur with my plan or do you have other advice? Sincerely, Walker
I am certainly no specialist in the area of siding, but I am sure a good quality spar varnish would indeed protect adequately. But how that affects long-term durability, re-coating, and appearance is not something I can really comment on.
Hi Marc
Have you ever used spar Varnish or any other varnish to seal tile grout. Or do you have any other long term solution.
Thanks
Oh that’s an interesting thought. No I haven’t and I’m not sure of the long term ramifications of something like that. You would think the grout sealer companies would have something decent on the market. Do those products not work to your liking?
Hey Marc, does spar varnish provide any extra water-proofing over poly? I am looking for a good finish for some cherry coasters, which will obviously get wet from time to time. The coasters also have some CNCd images “engraved” into the tops, if that matters.
Thanks!
Spar varnishes are supposed to be more water-resistant than indoor polys. But I think that’s more related to the fact that the material is more flexible. So if the wood absorbs moisture, the finish will expand and contract with the wood and won’t crack. For something like coasters, personally, I’d go with a high solids varnish, something like Behlens Rock Hard.
Hi, I have 22 exterior doors that bake in the Arizona sun. The door are made of fiberglass with a wood grain pattern molded into them. The were originally stained with a gel stain and varnished. The finish lasted 4 years. I had a professional refinish them and the job only lasted one season. The painters explanation was that VOC rules in Arizona only allowed him to use crappy varnish.
Can I steel wool these doors, gel stain them and then use the Epifanes spar varnish on them?
Thank you.
As long as you prep the doors adequately, you should be able to apply more gel stain and then Epifanes. I’d be curious to hear how the Epifanes holds up.
I guess I will try it and let you know. Thanks again
I am planning a post fence of 5″ diam. Eucaliptus poles, and plan to treat these with bora care to avoid ground termites. Afterwards i am planning to varnish these with a non yellowing, glossy clear varnish. The poles are exposed to the elements, verydry heat and occasional heavy rain.. What do you recommend?
I would probably go for what I like to call the “bulletproof” finish. A pre-coat of CPES (Clear Penetrating Epoxy Sealer) followed by as many coats as you want of Epifanes. This is a very protective film finish that should last a good long time. In all liklihood though, this finish will yellow a bit with time since the product is oil-based. If you really need non-yellowing, you might look into some water-based or outdoor deck specific products (which I am not too familiar with).
We’ve recently built a kitchen bar counter out of old, weathered pallet wood. It’s beautiful and rough, with spaces between the pieces that can catch crumbs. I would like to protect the wood (and us from splinters) without changing the color, adding gloss or creating a hard plastic feel. Someone recommended spar varnish. Is this the best option?
Hey Kathy. You can use spar varnish, but I would try to use it as part of an oil/varnish blend. That’s a good way to keep a fairly natural look without compromising completely on protection. Here’s an article that might help you further. http://www.thewoodwhisperer.co.....op-finish/
I keep hearing a lot about ‘the paint manufacturers put UV blocker or inhibitors’ In their formulations. The research I have done has only turned up one inhibitor compound and that is pigment. Could you please expound on what other UV inhibitors can be added to varnish? Especially inhibitors that will be useful for a clearcoat application?
Thanks..
In addition to pigments, one additive I have seen used in clear finishes is Ethyl-vinyl acetate. For instance, Minwax (Helmsman) Spar Varnish shows 3% pigments and 1.6% Ethyl-vinyl acetate by weight. I don’t know if this is standard practice for all uv-protecting varnishes but that’s at least one example.
I have a 1965 Starcraft boat with mahogany veneer on it. To preserve it I used Johnson floor wax. This made it worse. I believe the veneer was coated originally with polyurethane. The coating is pretty worn down. I would like to put spar varnish on it but I cannot do a lot of sanding on the veneer. Is there a coating you would recommend. What would you recommend to do.
Thanks,
Mike
Marc,
Thanks for the response! I’ve been researching and I believe I’m pretty set on a certain brand of epoxy finish. It is called Max CLR HP and has a nice solids content. Not too worried about the uv anymore (decided it would be interior only) but I could also put an exterior poly on if need be. Any opinion on epoxy finishes?
Thanks,
Ryan
I haven’t used them much so I don’t have a whole lot of experience to draw from. but if you don’t mind they thick film, they are fairly bulletproof.
Hi Marc,
I am in the process of building a folding table that will be subjected to moisture with great frequency. It is a beer pong table. But in all seriousness I like to do good work and I’m trying to make it look nice. It is made of clear redwood and I’ve been looking through a vast number of your very helpful tutorial videos for general finishing advice.
My dilemma with choosing a finish is being caught between two conflicting interests. I desire hardness but also a little bit of UV protection. I now know that marine spar is softer to deal with the constant expansion and contraction of a boat’s life on the sea but has pretty darn good UV inhibition (granted it has a good number of coats). A normal oil varnish like a polyurethane for flooring can be hard but offers barely (if any) UV protection. I realize redwood is soft but it also does well outside which was a factor in my choice of using it.
I would like to have something that is nice and hard with a little UV protection. I know you like the Epifanes but that seems like a pure marine spar (aka softer). Do you know of any coating, perhaps a marine deck varnish, that would address both of these needs?
Thanks
Unfortunately, I don’t. Just about any finish for an exterior surface is going to be flexible and less hard than it’s interior counterpart.