Polyurethane wood finish, the biggest seller, might not be the best choice for your project. We’ll look at it & 4 other finishes that might be better & easier when refinishing furniture. I won’t promote a brand (they’re all pretty good), I’ll simply outline the major finish chemistries so you can make an intelligent decision for this and future projects. Go to your local big box store and you’ll be offered numerous choices of clear wood finishes.
Which is best? Ask the clerks at two different stores or even two clerks at the same store and you’ll totally different opinions. Go online and there are hundreds of choices. Read clear wood finish reviews and discover that no two authors have the same opinion!
Refinishing furniture is something every DIYer tries at least once. The fact is there are 5-6 basic clear wood finish chemistries sold under different gimmicky names by different manufacturers. Each tweaking the 5-6 basic chemistries just a little to create their very own product niche. Furniture refinishing product sales is a REALLY BIG business!
The truth be known that Teak Oil is not made from nor for just teak, Danish Oil wasn’t made from the remains of deceased Danes, Tung Oil isn’t made from anyone’s tongue and Tru Oil isn’t the only true oil. They are all made from one or a combination of the 5-6 basic finish chemistries and renamed to SELL MORE PRODUCT!
Our Clear Wood Finish Choices
In this article you’ll end up being able to select the right finish for your project. You’ll have 5 clear wood finishes (and one special use) in your arsenal with the knowledge of which is best for your given set of circumstances. Each is slightly different and each has specific uses and non-uses.
Practicality vs Beauty
Longevity vs Periodic Maintenance
High Gloss vs Satin Appearance
Environmental and Food Safety vs Volatile Chemical Petroleum Compounds
Durability vs Repairability
Indoor vs Outdoor Usage
Already thinking “I want them all”! Don’t fret I’ll talk about a combo that you can easily create, easy to apply, can be used in virtually any situation and a lot less expensive than you’ll find on the specialty shelf.
Oh, I won’t endorse a manufacturer, I’m not here to sell you anything. There are no links to purchase (red flags). Instead you’ll know the best type finish and can shop for whatever is on sale. My objective is to eliminate the confusion, save you time and money and give you clear choices that best match all your present and futures project needs.
A LITTLE ABOUT ME
They call me the “Finish Maestro” (actually nobody calls me that, but it would be cool if they did). My name is Paul and I started woodworking in 1973 (long before most of you were born). I am pretty much a guy who believes that I can do almost anything given reasonable guidance. YouTube is my bible for plumbing, electrical, appliance repair, automotive repair, etc., etc., etc. These are things I know enough about to be considered dangerous. Thanks to others knowledge sharing and the Google/YouTube platforms most of the danger is removed.
My strong suit is wood so about 7-8 years ago I made my first video on Bubble Free Polyurethane Application Technique. It was intended as a sort of payback. The reviews I read on blogs trashed various manufacturers complaining about the product bubbling. Trust me it’s not the product. It’s the application methods.
That video has 1.5 million views with a 95% like rating. Today my Videos and Blogs will add up to a complete guide from start to finish in Furniture Refinishing and Finishing.
By the end of this article or my accompanying YouTube Video you will have in your arsenal two surface coatings, two penetrating finishes and one combo that will eliminate the confusion, save you money and you’ll be able to quickly choose a clear winner for whatever use, look, feel and setting your project needs.
WARNING: I by nature am a detail guy. There’s a lot of information ahead. It’s simplified and practical but thorough (I think). I personally like to know the “whys” as well as the “how to’s”.
If you are in a hurry consider skipping to the summary at the bottom of this article. That said, if you are in that much of a hurry you might be best turning your project over to a professional finisher. A nice finish takes time, a little knowledge and a lot of patience.
Five Clear Wood Finishes That Should Be In Your Arsenal . . . Let’s Go
Clear wood finishes are classified as either surface coatings or penetrating finishes.
There are 4 major categories of clear wood “surface” coatings used in refinishing furniture: urethanes, lacquers, shellacs and varnishes. We’ll zero in on two and keep a third for a unique set of circumstances.
Quick clarification on the term varnish. Many mistakenly use the term varnish to cover all clear coatings. While I’m not a chemist in simplest terms varnish is made from an alkyd (polyester) resin, lacquer and shellac from bug secretions of the LAC bug and polyurethane a plastic resin. They’re all different. Nuff said!!
All surface coatings work the same in principal. There is a hard resin combined with a liquid solvent to create a thick liquid paste. This paste is thinned (further liquefied) by a material referred to as the carrier. Carriers are either water (for water-based products) or petroleum based thinners such as mineral spirits (for oil based products). Once applied and exposed to air the solvent and carrier evaporate leaving behind a solid, protective, hard, clear resin shell.
SHELLAC (NOT IN OUR AERSENAL)
Shellacs, once very popular, are not in widespread use today but they still have unique niches. Shellac has been widely replaced after the development of polyurethane and lacquer finishes.
Shellacs are not water, heat or chemical resistant. Wet cups and glasses tend to leave rings. Shellac melts when in contact with alcohol and heat.
Shellac is still used in finishing acoustic instruments due to its unique ability to preserve sound quality. Shellacs are also used in a very diluted (thinned) form as a wood conditioner. After thinning it can be used as a sealer on raw wood to avoid wood stain blotching and after wood is dyed to lock in color. Virtually any other coating will adhere to shellac.
LACQUERS (PROFESSIONAL LACQUERS ARE NOT IN OUR AERSENAL)
Lacquer is a great finish. Catalyzed lacquers used by manufacturers and serious hobbyists dry almost instantly, can be recoated within seconds and do not require sanding or other preparations between coats. Lacquer for the most part possesses all the qualities of polyurethane.
It is the choice of industry mass production and serious hobbyists because it’s fast, economical and efficient. It dries completely within seconds and cures within a few days. For industry this is a mass production, assembly line miracle finish.
To get the maximum benefit and advantages of lacquer its best sprayed on with professional spray equipment using an air compressor or an HVLP spray system. For this reason it’s not in the average DIYer’s arsenal.
BUT let’s not completely eliminate it from an occasional use. I don’t recommend spray can lacquers found in hobby, paint and hardware stores for all but the smallest of applications or where protection without appearance is acceptable.
Spray can lacquers are not the same as commercial catalyzed lacquers. They’re hard to control and thus difficult to get a professional looking finish.
If you do find the need for spray can lacquers it’s important to apply it in extremely thin spray coats. Otherwise drips, runs, or a common flaw called orange peel (a bumpy finish that resembles the skin of an orange) are the rule.
When I spray can lacquer I spray so thin that I know I often miss areas. Don’t worry you’ll get it on subsequent coats. Because it dries so fast you can recoat within 5 minutes (at 70 degrees and 50% humidity). That means it’s possible to do 6 plus coats in just 30 minutes. That’s important because any area I missed with one coat will probably be hit with the next coat (or the next).
TIP: It’s important to understand that with “ALL” surface finishes that thickness is built up in ultra-thin layers. You’ll hear me use the phrase “LAY IT ON THIN” in all my surface coating articles and videos.
So that leaves us with our two main surface coatings. Polyurethane and Spar Varnish. Finish-wise both are very similar in appearance and durability, but differ dramatically in their usage.
Polyurethane is the most common clear wood finish choice for refinishing furniture. Chemically it’s made with an acrylic (plastic) resin.
It’s relatively inexpensive, easily applied and extremely durable. With proper guidance it will deliver a professional looking finish without commercial grade equipment.
Polyurethane is waterproof and resistant to heat and chemicals. It is a VERY protective and an extremely durable wood finish that cleans easily and always looks fresh.
Polyurethane should be your number one choice where excessive use and abuse are the rule. Surfaces like desks, kitchen tables, floors, stairs, wood trim, widow sashes and sills, bar and counter tops, railings and chairs are all good candidates. In the proper environment polyurethane will last a lifetime with little to no maintenance.
POLYURETHANE H0W MANY COATS
As with all clear wood finishes surface protection and durability is dependent on thickness. For a durable, high quality, professional looking finish thickness is best achieved in multiple ultra-thin layers. The opposite of this would be globing it on all at once which results in bubbles, puddles, runs and brush marks.
For most projects I recommend 3 thinned coats of polyurethane. For heavy use 4 coats and for minimal handling 2 coats can suffice. The desk above has three thin coats of oil based polyurethane that was applied with a brush.
HELPFUL HINT: The desk in the image above is made from Ash. Before I applied the forts coat of polyurethane wood finish it had an off-white appearance similar to the white of this page. Wetting any wood changes its color and appearance. If you wet the wood with a rubbing alcohol or mineral spirits you’ll get an idea of the color and hue after your clear finish is applied (Water will do the same but I avoid using water as it takes too long to evaporate).
TIP: Wood with a high moisture content should not be covered with a surface finish. Moisture will inhibit adherence and result in peeling and cracking.
Polyurethane is available in 3 sheens: gloss, semi-gloss and satin.
Today’s esthetic preference leans toward satin finishes. Satin polyurethane finishes contain non-visible, microscopic silica (sand) crystals which tend to absorb light rays creating a duller looking appearance. Think of satin cloth material. It has a shine at an angle that tends to disappear when looking straight on.
It’s hard to show sheens in image form. In this and the next two images look at the reflection of the overhead lights on the surface and note the reflection of light surrounding the light spot.
SATIN CAVEAT: Too many coats of satin finish (four or more) tend to create a cloudy, hazy finish. If for some reason you want a satin finish and extra protection from over 3 coats I would use gloss finish for all coats but the final one or two. Or as another option you could apply use gloss on all coats and then knock down the sheen by lightly scratching the finish with a #0000 steel wool or 400 + grit sandpaper.
Gloss finishes are designed to bounce light rays directly back at the viewer. It produces a shiny, glossy surface. Think of a freshly waxed car in bright sunlight.
GLOSS CAVEAT: If you look closely at the images above the higher the gloss sheen the more imperfections become highlighted. Gloss polyurethane makes wood shinny not deep nor reflective. Putting a gloss finish on an old fashioned washboard will make the washboard look shiny not level its ridges and valleys which is required to achieve depth.
Depth of finish comes from sanding to highly polished surface (600 grit and finer) and filling the woods pores and grain with grain fillers and sanding sealers. Otherwise it will not achieve a deep, highly reflective finish like those seen on a baby grand piano or roadshow auto. Gloss polyurethane (or lacquer) is a very small part of the equation.
HELPFUL HINT: Polyurethane or any other clear finish (with the exception of two part poured on epoxy) cannot be used to fill defects. It will not level dents, deep scratches, know holes, open pores or heavy grain patterns.
POLYURETHANE APPLICATION OPTIONS
Polyurethane does require a little knowledge to achieve a quality, professional looking finish. It can be put on with a brush (preferable for larger flat surfaces) or wiped on with a rag (for things like spindles, bowls or carvings). As you can see in the photo below there is virtually no difference in appearance.
For speed and convenience I would brush large flat surfaces and wipe on small or rounded surfaces.
I have two videos and supporting articles that cover proper application. Each requires a little different thinning and some basic knowledge and technique.
THINNING POLYURETHANE – A CRITICAL STEP TO A PROFESSIONAL FINISH
Manufacturers were forced by EPA (environmental Protection Agency) to reduce the VOCs (Volatile Organic Compounds) in their products to comply with environmental regulations. They often label their cans with a warning “Do Not Thin”. This in my opinion is the advice of their legal department and not their engineering departments.
Polyurethane used directly from the can is too thick to assure good results. I thin all my finishes and I now do it on EVERY coat. Thinning assures proper flow and minimizes bubbling, puddling, running and brush marks.
On my how to video “Bubble Free Polyurethane Application Technique” I often got comments like “I wish I would have watched your video first. Now I have bubbles and brush marks. What can I do to correct this?” The question became so common that I did some research and produced a video called “Fixing Polyurethane Bubbles, Puddles, Runs and Brush Marks”. Please watch the proper application videos to avoid having to watch the fixing mistakes video.
Speaking of videos many DIYers watch misinformed novice authors who advise brushing on polyurethane in back and forth motions like applying paint. They don’t even talk about thinning the product before using. While this will certainly coat the surface it won’t render the appearance that we are typically after.
WATER VS OIL BASED POLYURETHANE – THE GREAT MISINFORMED DEBATE
I recommend and typically use oil based polyurethane unless the goal is to keep the wood as whitish as possible. The difference is negligible (see image below). There are so many advantages to oil based polyurethane over water based polyurethane (especially for beginners).
Oil Based Polyurethane Advantages: Under normal conditions oil based polyurethane sets up (becomes tacky) in about 15 minutes whereas water based polyurethane sets up in about 5 minutes. Longer set up times allow tiny bubbles to pop and brush marks to level.
Oil based polyurethane is tougher than water based polyurethane.
Oil based polyurethane is more flexible and has less propensity to crack over time.
Oil based polyurethane highlights the woods character more than water based polyurethane.
Oil based polyurethane is more resistant to heat than water based polyurethane.
Oil based polyurethane is less affected by UV rays than water based polyurethane.
Oil based polyurethane application is more forgiving to beginners than water based polyurethane.
Water Based Polyurethane Advantages: It eliminates having to clean brushes with mineral spirits before washing.
Water based polyurethane is clear whereas oil based polyurethane adds an amber cast.
THE CONS TO ALL POLYURETHANE
Yes there are some downsides to polyurethane.
If damaged polyurethane is difficult to repair and for even the most experienced woodworkers often requires complete removal and refinishing.
Polyurethane is not food safe. While you can use it on counters it is not recommended for direct food contact by placing, prepping or cutting edibles on its surface.
I recommend finishing all sides (top/bottom and both insides/outsides). Because polyurethane envelopes the wood doing one side only results in uneven seasonal wood expansion and contraction. Uneven contraction and expansion can result in finish cracking and peeling.
Polyurethane is essentially a plastic coating offering protection and durability. While it provides a really nice finish when done right, it doesn’t quite measure up to the luxurious look and feel of penetrating oil finishes.
Polyurethane yellows slightly over the years but that is more due to the wood aging.
Unless modified for outdoor use it should be restricted to indoor uses.
VARNISH – AN OLD FINISH WITH POSITIVE POINTS
Varnish has many of the same properties and is thinned, applied and handles virtually the same as polyurethane. Chemically varnish is made with an alkyd resin.
Varnish is a softer more flexible finish and as a result handles weather related expansion and contraction much better. It also is not affected by ultraviolet radiation and is fully waterproof. Varnish tends to yellow with age and has a softer feel and thicker more amber look.
I recommend polyurethane for inside projects and Spar Varnish for exterior use. Spar varnish (alias marine varnish) was originally formulated for protecting wooden boats.
Its base is an alkyd resin. Today it varies chemically with each manufacturer. I recommend spar varnish suspended in tung oil. Some manufacturers have eliminated the tung oil.
Spar varnish made with tung oil is easily repaired when damaged. It adheres well to previous coatings and because of its soft texture it blends well after repairing.
In addition to its weather related properties and repairabilty, it adds a warmth not seen with polyurethane. We’ll use tung oil based spar varnish indoors as part of our combo finish.
Tung oil based spar varnish is typically available in gloss and satin sheen. It is an oil product so it is always thinned with mineral spirits (or thinning agents like paint thinner, naphtha, turpentine). Here again we apply ultra-thin coats. 2-3 thin coats are the norm.
For the everyday use of a kitchen table, desk, stairs, bath vanity, etc I would go with polyurethane or lacquer (lacquer applied with professional spray equipment). For the fine furniture, decorative wood pieces, fine antiques, food safety and environmental concerns or an occasional use dining room set I would probably choose the luxurious look and feel of an oil finish.
A LITTLE ABOUT OILS
All oils will keep wood moist, supple and repel liquids. Oils used for furniture are classed as drying oils because they become dry to touch after exposure to air. Oils in nature are either petroleum based or biologically based.
PETROLEUM BASEDOILS FOR FURNITURE REFINISHING – REALLY??
I like to use pictures so when I wrote this I thought it’d be funny to pour motor oil on my kitchen table and take a picture. But after 53 years of marriage I instinctively knew that wouldn’t be wise.
So I went on Google Images to see if anyone was dumb enough to do it and photo it. Turns out a lot of DIYers coat their fences, sheds, flat bed trailers, etc with used motor oil. Oh well!!
You could essentially use any oil on wood. If you pour motor oil on your kitchen table it will moisturize and protect but it will remain tacky and messy for years.
Most oils are classified as non-drying oils. That’s why the motor oil that didn’t do well on your kitchen table works so well in your automobile. Also the Food and Drug Administration would have a problem with placing motor oil or any petroleum based oil on your dinner table.
The exception would be highly refined petroleum based oils like mineral oil (sold under many trade names like butcher block oil, salad bowl oil, cutting board oil, etc.). The problem is that refining oil to that degree degrades the very nature of the oil causing it to evaporate in a short time frame. This type oil requires re-oiling frequently as maintenance.
PLANT BASED OILS – A BETTER CHOICE
Most oils suitable for use on wood are found in nature and are plant based. Here again we see so many plants based oils sold for wood protection.
There are three problems with the vast majority of plant based oils:
Many break down and evaporate too fast (requires constant maintenance);
A lot remain wet and tacky for very long periods (non-drying oils);
Almost all have an issue with turning rancid (plant oils are biological fats which spoil and rot over time);
The majority are poor at water repellency (offer minimal wood protection)
LINSEED OIL vs TUNG OIL – THE WINNERS
There are two oils that stand out and most commercially sold oil finishes have one of the two as their base. They are classified as drying oils (become hardened at normal room temperatures) making them acceptable wood finishes.
Linseed oil comes from the seed of the flax plant. It has two issues when used on wood: It has an extremely slow dry time, it’s too thick to apply properly and it while its liquid resistant its not liquid proof. To resolve these issues linseed oil has been chemically modified over the years.
Today linseed is commonly sold as Boiled Linseed Oil (BLO) and contains petroleum based thinners, heavy metal stabilizers, drying agents and mildew retarders. Each manufacturer’s product formula is different and some add a polyurethane or varnish resin to the mix which aids in waterproofing.
Once modified it becomes an inexpensive, easy to apply, fast drying finish that produces a durable and beautiful appearance. It accentuates the woods patterns and grain.
The cons of BLO is the additives and resistance to liquids. It is not considered a food safe nor a GREEN PRODUCT. Also because each manufacturer modifies it differently the finish is often not consistent from one manufacturer to the next.
Today a few manufacturers offer Polymerized Linseed Oil (sometimes called Purified Linseed Oil). Here the oil is superheated (300 degrees F) in airtight tanks for a few days. The polymerization process alters the viscosity and enhances the speed of drying.
This process adds considerably to the cost. While the product is now rendered an eco-friendly and green there is still an issue with rancidity and its resistance to liquids.
My all-time favorite finish for beauty, durability and ease of repair is tung oil. It is liquid proof, heat resistant, UV resistant, mildew free, additive free, food safe and durable. Oh and did I mention it is by far THE MOST luxurious wood finish enhancing the beauty, feel and texture of the wood.
CAVEAT: Finishes sold as tung oil may or may not be tung oil. Because in pure form has an extremely slow dry time and thick viscosity tung oil like Boiled Linseed Oil it is often sold in a highly modified form. Manufacturers have it modified to a point where there may be little or no actual tung oil in the product. Be sure your purchase is labeled Pure Tung Oil or Polymerized Tung Oil.
TUNG OIL FINISH – most products labeled tung oil “finish” are highly modified and not recommended.
PURE TUNG OIL
For years I used Pure Tung Oil on my projects. You can see the procedure I follow in the post “How to Apply Tung Oil Properly -Tips & Techniques“. It’s a great system for those with time as the application process can take weeks due to the extremely slow dry times.
POLYMERIZED TUNG OIL
The game has changed and super-heating pure tung oil in the absence of oxygen changes the chemistry and renders it a fast, easy and virtually foolproof for all skill levels. Polymerized tung oil allows the most novice DIYer to get a professional finish in their garage or basement without expensive spray equipment or brushes.
You apply it with a rag and the next day (at normal temperature and humidity) perform a very light sand and reapply (4-5 coats recommended). This is my GO-TO oil finish.
TUNG OIL PROS
Easy to apply
Easy to repair
Long lasting (decades)
Won’t turn rancid
Water and Liquid Proof
Chemical and heat resistant
Food Safe (Pure Tung Oil & Raw Linseed Oil Only)
TUNG OIL CONS
Polymerized Tung Oil tends to be pricey
Polymerized Tung Oil becomes food safe after thinners evaporate.
PAUL’S COMBO FINISH
Varnish adds a softness and warmth to wood and tung oil accentuates the wood’s grains and patterns while adding a luxurious glow and feel. So let’s mix our own special finish that will put all the high priced specialty finishes to shame.
Basically I combine Polymerized Tung Oil with Tung Oil based Spar Varnish. I’ll be publishing a post on my website with complete details and mixing instructions very soon (I promise).
Sheer beauty and a luxurious feel.
Easy to repair when damaged
Chemical and heat resistant
Won’t turn rancid
Not Food Safe
FOOD SAFE WOOD FINISHES
Pure tung oil, shellac, mineral oil, walnut oil and raw linseed oil all food safe with no volatile organic compound emissions.
Shellac is not waterproof, heat or chemical resistant and therefore becomes a poor choice in food prep areas. Raw linseed oil is slow to dry and not waterproof.
Pure tung oil can be thinned with citrus oil which makes application easier but is still slow to dry. Polymerized tung oil comes thinned with a thinning agent (mineral spirits, naphtha, turpentine, paint thinner, etc) but requires complete evaporation (30 days) before it becomes VOC free and food safe.
Mineral oil is a petroleum product but highly refined. It has been sanctioned by the Food and Drug Administration for use in food prep areas. Walnut oil and some of the other plant based oils are food safe but are subject to rancidity and along with mineral oil requires regular reapplication due to evaporation.
SUMMARY: Quick Overview, Comparison Chart and More
So here’s our arsenal and ideas of when to use each
Polyurethane – indoors on high use surfaces that need a high degree of protection from liquids, heat, and physical abuse. Examples: Kitchen tables, desks, work surfaces, bar counters, railings, ballasts, wall and window trim, floors, steps. (NOT FOOD SAFE)
Boiled Linseed Oil – liquid free projects where a nice inexpensive oil finish is desired. Decorative wood pieces and furniture where fast dry and cost is a concern (NOT FOOD SAFE)
Tung Oil – the ultimate in luxury, texture, feel and esthetics, wood kitchen counters, salad bowls, cutting boards LEFT UNTHINNED POLYMERIZED AND PURE TUNG OIL ARE FOOD SAFE AND VOC FREE WHEN APPLIED WITHOUT THINNING
Combo Finish – same as tung oil with a little more durability. Fine furniture, antiques, wood carvings, decorative pieces, expensive flooring/staircases. The varnish adds warmth and a slight sheen not readily achievable with pure or polymerized tung oil alone. Should not be used where food safe applications are a consideration (NOT FOOD SAFE)
Rattle Can Spray Lacquer – this isn’t a particularly nice finish but for small detailed pieces (hard to brush or wipe on finishes) like carved pieces or projects where appearance isn’t important they fast easy and inexpensive. A bad choice for flat surfaces or medium to large projects. (NOT FOOD SAFE)