If you are finishing wood with a natural or stained appearance today, you’re likely using some kind of varnish or polyurethane. Varnishes create a hard finish that protect and beautify everything from wood floors to delicate woodwork, but do you know the difference between a spar varnish and regular varnish and when to use them?
Wood finished for outdoor use is subject to a completely different set of factors that indoor finishes never have to deal with. Huge temperature swings, big changes in humidity, and punishing UV rays are the primary effects your finish will have to endure. These elements will easily break down a regular varnish or polyurethane over time.
Humidity changes, for one, cause the wood to swell and shrink much more than wood left indoors, and that excess movement alone is enough to crack a regular varnish in short order. So, for an exterior wood finishing solution, we turned to boat makers and their years of experience in caring for wooden elements with the harshest exposures in the world.
What is Spar Varnish?
The term “spar varnish” comes from the boating world, where the long wooden poles that support the sails are known as spars. A spar varnish is a finish specifically designed withstand the rigorous conditions of seafaring life, which means it can also handle anything your backyard throws at it.
The Components
So, what’s in it? Well, every varnish or polyurethane is made up of relatively similar ingredients. Just like with the grocery store, if you can cut through all the marketing hype and look at the actual ingredients, you’ll be able to make a better decision.
They all contain, in varying amounts, an oil, resin, and solvent. Manufacturers like to play around with the amounts and kinds of each to make their varnish, but this basic recipe is always followed. Within those three ingredients, you also have a couple options.
Oils
Linseed oil and Tung oil are the most commonly used oils in varnish and they create a deep penetrating finish. If your finish were only oil, then you’d have a very slow drying and soft finish that penetrates deep within the wood. Using oils alone is an option, but it takes many coats to build up a thick enough coat to protect the wood. These oils are an important part of a good spar varnish, because by adding more oil to the mix, you get a softer and more flexible finish that can handle the excess movement associated with outdoor wood. Higher oil content is one of the markers of a good spar varnish.
Resins
Resins are the hardeners. Typically, the resin is either alkyd, phenolic, or polyurethane. Alkyd and phenolic are associated with varnish finishes, while the use of a polyurethane resin is what makes a finish a polyurethane. These ingredients give us the hard, shell-like finish you are accustomed to in most varnish finishes. Interior finishes are relatively high in resin content and low in oil content, which creates a nice hard finish, but leaves little flexibility and penetration. Without the resin, you’re left with an extremely soft finish that may not hold up to traffic and wear.
Solvents
These resins and oils need a carrier to be dissolved in, and that is what the solvent provides. There are a multitude of solvents, but mineral spirits and paint thinner are the most common. There are others like naphtha and xylene that are faster drying as well. The solvent thins the oils and resins and helps blend them together and make them easy to apply with a brush or wiping cloth.
UV Blockers
Last but not least, every spar varnish needs to protect itself and the underlying wood from the sun. Regular polyurethane and varnish contain little, if any, UV blocking additives, and that alone makes them a poor choice for exterior application. Without UV protection, varnishes and wood quickly break down and fail.
Selecting a Varnish
Like most things in life, you get what you pay for. Better ingredients result in a better product and those better ingredients cost more. Will it kill your project to use a cheaper finish? Absolutely not, but considering the amount of work you put into your project, wouldn’t a few extra dollars be worth it for a longer lasting finish?
For me, there are two options I usually go to for exterior wood finishing. Both are excellent choices, though one does stand above the other.
Helmsman Spar Urethane
This spar urethane is probably the most readily available spar urethane on the market today. You’ll find it in just about every big box and local hardware store. According to the ingredients we discussed earlier, Helmsman uses a polyurethane resin, hence the name and the primary solvent is mineral spirits. It is easy to apply and creates a nice warm finish that stay flexible for years. You can find it in a variety of gloss levels as well.
Epifanes Spar Varnish
You won’t find this on your local hardware store shelves, but that doesn’t mean it’s not incredible stuff. Personally, this is my favorite finish for exterior wood. It was designed by boat finishers for boats and us land lovers can benefit from their hard work by using a product that can handle the toughest elements. It uses a phenolic resin, which I think is better suited to outdoor use, and the solvent is naphtha with a little bit of xylene. You can usually only order it online. If I’m finishing an exterior wood project, 9 out of 10 times Epifanes is the stuff I reach for.
The Conclusion
What it all comes down to is protecting wood, and for exterior applications, spar varnish does a better job of it plain and simple. Just like you need the right tool for the right job you also need the right varnish for the right application. Finding the right varnish is only half the battle, though. You need to know how to apply it properly and we’ll be talking about that next week.
The main reason most finishes fail prematurely is not because of an inferior product, but because of user error. Poor preparation and application can’t be overcome by a premium product. So, tune in to learn how to get a great finish next week.
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I love old houses, working with my hands, and teaching others the excitment of doing it yourself! Everything is teachable if you only give it the chance.
I have sanded and in the process of staining and outdoor wooden table . I am using one step stain and varathan once I am done can I put marine grade varathane over top to seal everything ?
I am building a bar table for my husband’s pole barn, out of reclaimed hardwood that I have sanded down. It will be subject to the extreme heat / cold, but be out of the weather. Is spar varnish the right choice?
No, I use a lot of varnish’s however for a bar top I would and have used epoxy
I have covered porch with a new kiln dried treated lumber floor. The wood has been installed 5 months ago so a long time to get low moisture especially with kdat
We applied a water based gray stain and two coats of helsman spar varnish. The third coat was supposed to be semigloss but painter mixed the cans and about a third of porch had different gloss. He came back put an overcoat of semigloss over entire porch. Three days later there are patches of brown stains. Looks like the brush had a darker stain mixed in but pretty sure that’s not the case. My question is this. Have you seen the browning occur before? Thanks for you help
Hi – I have a wood outdoor patio table. Nothing fancy – bought from a big box store but I know that in its out of the box state it probably won’t stand up to the weather and sun. Could I apply spar varnish over top of the table or would it need to be sanded down to a raw state beforehand etc? Thanks for the advice.
I’m building a hovercraft and used red oak for gussets on the ribs.Is it better to use spar varnish on them instead of epoxy resin.I just found out red oak is prone to rotting,
Can spar varnish be used over paint? A painted exterior sign?
Yes it can.
I have a STickley African Mahogany wood front door that was installed 8 years ago. It came as a raw wood door and was stained with a spar varnish by our painting contractor. Now the exterior of this door has faded dramatically and needs to be restained. Cole Hardware is telling us we need to choose a color stain or paint before we apply the spar varnish. From what i can tell of the original finish only the spar varnish was applied. Is that possible? The inside of the door currently is a dark brown/reddish finish with the wood grains visible. The front of the door is now almost blond in color. How do we restore the front of the door to look the same as the interior side of the door? Will just the spar varnish alone bring back the deep brown/reddish finish?
Any advise would be appreciated
Hi Scott~
Several years ago we had mahogany decking, handrails and post caps installed on our front and side porches, along with beadboard ceilings. At the time I requested spar varnish be applied to give maximum protection to the wood. The builder, and subsequent house painters all said that this was not the recommended finish for the product. Now the ceilings are dingy and the stairs and handrails are split. On our side porch, the entire support structure of the stairs is falling apart, so will need to be replaced. What is your opinion on using spar varnish on this type of application?
On another note, we have some acacia folding chairs and tables that are in need of a sanding and restaining. They are in great shape as they are in a covered area and stored every winter. Do you think spar varnish would be a good finish for these?
Use spar varnish only for exterior wood. It’s too soft for interior applications. Just use a good interior polyurethane. You can use the spar on the acacia pieces outside. The softer formula makes it able to expand and contract with the wood better, which helps prevent the finish from cracking. It also contains a UV filter which is needed to protect the wood from breaking down in outdoor conditions. I recommend oil-based poly over water-based formulas. It takes longer, but the resulting finish is 10x better looking.
I just put 3 coats of spar urethane on a outdoor barn quilt and it is now yellow instead of white. I thought it would be clear. The background paint is white.
Is this normal?
Hi Scott. We are considering making a bathroom counter top with hard maple. What product do we need to seal it and be sure it is waterproof?
The best solution is an epoxy coating, followed by several coats of oil-based polyurethane. It’s expensive, but it’s the best way to go.
I have a log home that was originally covered with Bennett’s Log Oil. After they went out of business, I used Ponderosa Log Oil. The finish sits on top of the wood and has a glossy smooth finish which I like. Because the finish sits on top of the wood, stains don’t really penetrate. That’s fine with me. Can you recommend a similar product? I’m considering mixing 1/3 spar varnish, 1/3 boiled linseed oil, 1/3 mineral spirits but would prefer to find an available product that has good UV protection and has been tested. Any help?
Hey Scott,
I’m redoing my 100 year old windows and need to know what kind of varnish should I use for the interior side of the windows? I want to keep the stain and I’m assuming I need a varnish where the wood and glass meet to seal the glazing putty?
Hi Scott, I have a question about kitchen wooden counter tops. If you were finishing a wood counter top, what would you use for a high gloss, but low scratch potential, varnish? (or should I think semi gloss?) I used Spar varnish once for a mahogany door threshold and it’s lasted for years and years, but did get scratched as you would expect being in a foot traffic area. I’m contemplating doing some wood counter tops and would like more info on how they would hold up with varnishing before I make a final decision.
We have an upcoming bathroom remodel. We saw a blog post for a wood floor company that said that we should use a spar poly on bathroom hardwood floors. It sounds like a good idea since the bathroom has humidity and wet and temp changes. My husband brought up the fact that if that were the case then more people would recommend that. What do you think?
It’s not a terrible idea. The spar is softer than regular so it may dent and wear easier but especially without a bath fan it could be a good idea.
Another place you can find the Epifanes is at any Marine /boating store. I live near the coast in California and there are quite a few shops for boating needs.
Thanks for the heads up on Epifanes…any particular source for buying it? The other point that i would like to bring up is sheen levels. The high gloss is the natural state of most varnishes, spar or otherwise, and in order to take that down a flatting paste is added. That also softens the surface which for most cases may not be desirable, so i usually lay down a base coat of a high gloss, then scuff sand and apply the finish sheen level desired. If high gloss is what you’re after, a paste filler with stain is my first coat for open grained wood (oak, mahogany), wiped off against the grain, then 3-4 coats of high gloss spar with the 1st coat thinned a bit, with a light scuff sand between coats. I don’t care much for the polyurethane as it doesn’t cross link where the traditional spar varnish does. The poly depends more on a mechanical bond when recoating, whereas with the traditional, a chemical bond (cross link) occurs. This simply means a scuff sanding (after scraping any loose material) is all you need to maintain it. The poly requires much more agressive sanding (more work) to acheive the mechanical bond needed.
Thanks Mike! For epifanes try either Amazon or Jamestown Distributors for the best prices.
Thanks Scott,
I suppose that for timber framing pergola it can work also, but the price must indeed be high (thought of just tung/linseed oil mixture). But for restored OR new wood outside door, would you go for Epifanes Matte Finish ?
Cheers
Epifanes for the door yes. For the pergola you might also consider an exterior stain like Sikkens.
Thanks Scott !