What's the Difference Between Polyurethane, Lacquer, Shellac, and Varnish?

These terms for a finish or topcoat are often used interchangeably, but there is a big difference. Learn when and where to use the right one.

Choosing the Right Finish 

A durable top or finish coat can limit the ravages of time and use of a piece of furniture. While the names varnish, polyurethane, lacquer, and shellac are commonly used to reference a final finish in general, these products are not the same, nor are they advised to be used interchangeably.

Shellac

This finish is a natural product (it's made from blending a secretion from the female lac bug with a solvent such as alcohol) that is very safe once dried and hardened. In addition to adding a protective coating, it also can add a warm amber color to wood. It can be affected by heat or chemicals, so a kitchen table might not be the best place to use it. Fine furniture items can be considerably enhanced with shellac. Some shellac manufacturers recommend using it as a protective coat on non-wood items. Apply it with a natural bristle brush or with a cotton rag.

Shellac is accessible in most home centers as a liquid in a can. It also comes in solid form or in flakes that must be dissolved, and it has a less shelf life than other finishes. The liquid variety is the best option for the average homeowner.

Polyurethane

Essentially a plastic in the form of a liquid until it dries, polyurethane is available in both water- and oil-based options, and comes in variations from satin to glossy.

Water-based polyurethane is recommended because of its low odor and low toxicity. It goes on clear without adding a slight color that oil-based versions can, and it dries much quicker. As with shellac, water-based polyurethane won't hold up well to heat and elements. It's good for bookcases, desks, side tables and picture frames — anything that won't be exposed to extremes.

Minwax Polycrylic is an example of a fortified water-based polyurethane than can stand up a bit better to rough conditions. It can also go over oil-based finishes and can be applied using synthetic-bristle brushes, a foam roller or a rag, and other water-based polyurethanes. Water-based oil-modified polyurethane is a relatively new product that combines an oil base's strength with a water base's cleanup. This product can be used on wooden floors.

Oil-based polyurethane is slightly more durable than water-based, especially when handling heat, so a kitchen table is a good candidate. It adds a slight color tone and will bring out the richness of timber.

When working with oil-based polyurethane, use a respirator in a well-ventilated area. Apply using a natural-bristle scrub or rag. Oil-based takes much longer to dry and cure than water-based, so plan accordingly and follow the manufacturer's directions.

Both oil- and water-based polyurethane can be applied to latex/acrylic paint; however, oil-based polyurethane will create a yellow or amber hue, especially light colors. To add durability without affected color, use a water-based coating.

You can also purchase polyurethane in a spray, which makes it a bit easier to apply, especially on huge projects. Wipe-on polyurethane is used primarily by woodworkers who want to create a "hand-rubbed" finish on special projects. These two run the extremes of ease of use but produce excellent results.

Varnish

The name of this finish often is used generically for a finish or topcoat. It's very durable because it contains a higher ratio of solids. Spar varnish is perfect for outdoor projects, and raw wood used for exterior doors and trims on rustic homes. In addition to protecting the wood, it also provides natural ultraviolet light protection. Spar varnish is often used on items near or the water, like a wood boat, decks, beach chairs, etc. Apply using a natural-bristle brush.

Lacquer

Lacquer provides the extremely intense gloss finish often used on many Asian-inspired or ultramodern furnishings. It is extremely durable and resistant to damage; however, it can begin to discolor and become scratched over time. Wonder why it's so smooth? It's applied via a sprayer because it is thinner than the other finishes. You'll need a high-volume, low-presser (HVLP) sprayer and a well-ventilated and spacious workspace to apply it.

Other Finishes

Cutting boards and other wood items that come in contact with food do well with butcher-block oil and food-grade mineral oil. Wooden tool handles will hold up better with an annual rubdown with boiled linseed oil.

A Few Words About Applicators

The general rule of thumb is to use natural brushes, sometimes referred to as China brushes, for all oil-based finishes, and synthetic brushes, sometimes referred to as nylon brushes, for latex, acrylic, or water-based finishes. Rollers and rags can work for either type of finish.

Because these are the top coats being applied, you'll want them to look as fresh and as smooth as possible. The best conditions to apply are when there is as little dust or other airborne particles as possible. Clean your work area as thoroughly as possible and allow some time for the dust (literally) to settle. Consider using a dust collection system or air purifier.

When applying a coating with a brush or roller, you may notice some bubbles pop up. 

Don't freak out. 

Many times these will settle out as the finish dries. If it's a problem, use a rag to wipe it down. You can often avoid this by applying a thinner coat. Also, shaking a can of finish will certainly add bubbles, so try stirring instead.

After the first coat dries, you'll need to either sand it with a fine-grit sandpaper (220 grit) or use steel wool. You may have heard to only use steel wool, but many manufacturers recommend either one. Just be careful not to scratch the finish deeply and certainly do not sand off the finish to the point where you reach raw wood. Wipe off the dust generated and apply another coat. A couple of coats are usually enough, but you can apply further coats (more wiped-on coats can be applied than brushed or rolled) to create a thicker and more durable finish. Try not to exceed four or five layers of finish.

 

 

 

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Filling polyurethane resin with used tea or coffee

I've just written some outline notes explaining fillers' uses with resins and posted them in the 'Materials/-casting' section entitled Common fillers for resin casting. Here you will find the various reasons for using fillers listed, i.e., to save on cost, to thicken the resin, alter the weight or strength of casts, or achieve a particular surface appearance. I've also detailed the fillers I know about how much they cost and where to get them.

I'm making some tests filling polyurethane resin with used tea-bag tea and coffee grounds, and here are the first results. The tea or coffee must be thoroughly dry, and I usually just spread them out on absorbent tissue where I leave them for at least a week but drying them out in an oven on very low heat would work just as well if they're needed sooner. 

For these tests, I've used Biresin G26 polyurethane resin from Tiranti, which is my favorite for its reliability. In each case, Parts A and B of the resin were mixed thoroughly but quicky first before mixing in an amount of coffee or tea and pouring (or spreading) into the oval mold. This is essential when filling resin with anything even slightly absorbent. In the first place, if the material is mixed with either part of the resin first, it will start absorbing it, meaning that some of it won't be combined properly with the other resin part when added. In the second place, the mix will quickly become too thick (whichever part is used first) to distribute the two resin parts evenly anyway.

Working from left to right, for the first form above, I mixed 25g resin (12.5g of each part) and could add 15g coffee grounds before I felt the mixture was becoming too thick to do anything with. It was certainly not pourable, but I could easily paste it into the mold, making sure that it was properly packed down evenly. As the resin began to set, the mix reached a 'dough-like' state fairly quickly where I could continue to press or even stretch it with my fingers—certainly more press casting than anything else. When set (c.15mins), the resin had filled the surface smooth, but the coffee had colored it a rich brown, and the coffee grains were visible underneath as an even speckle.

Next to it, I mixed tea and resin in equal weight (in this case, 10g each). Tea-bag tea differs from loose tea in that the particles are smaller, more like small grains plus dust. But these expand immediately on contact with the resin, and very quickly, the mix became like damp soil. But it was workable enough to trowel and press into the mold and like before, after a minute, or so I could press it down further with my fingers. The result was equally attractive but different. Because the tea is much more absorbent than the coffee and I had used less resin anyway, there was not enough of it to fill the surface, and the resultant effect is very much like a peaty soil pressed into shape. Unlike real soil, though, the resin had bonded the tea into a very strong, hard solid.

For the next sample, I used less tea (half as much, in fact, 20g resin to 10g tea this time). The mixture was still thick i.e., more of a paste, but much 'wetter' than before and could be more easily introduced into the mold. When set, the forming surface was smoother (albeit broken in parts) because more resin could coat the mold surface. The tea didn't stain the resin itself like the coffee had done because the used tea-bags been rinsed after use.

For the final sample in this small series, I added even less tea ( 20g resin, 7g tea) because I wanted the resin to coat the cast's surface uniformly. Still, after full curing of the form, I cut back the surface, a term used to describe using an abrasive on a filled cast's surface to expose the filler better. The result of sanding with coarse sandpaper, below, was a surface that looks very like sandstone but is much easier to carve.

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Power Buffing Polyurethane For Flawlessly, Glass-Smooth Results

If you pay heed and get the details right, you'll be one of those who can apply a great finish on wood, and do it each and every time. It all comes down to a trick called "buffing."

Why Is Polyurethane Finish Buffing So Efficient?

Buffing wood is the best-kept mystery of the wood finishing world. What amazes me is how few woodworkers know of it, considering how often people have difficulty creating a wood finish they can triumph. Buffing can create a glass-smooth finish, even after polyurethane has been applied not-too-well with nothing more than a brush in an ordinary home workshop. Buffing is particularly valuable for dealing with waterbased urethane's dirty side – the brush strokes, the bubbles, and the less-than-smooth results many people struggle with. The dirty little secret of the wood finishing world is that waterbased waterbased urethane is significantly more difficult to apply than its oil-based ancestor. Buffing does make it easy to get superb results on wood finished with polyurethane. That's what you'll learn about here. Buffing works beautifully, even if you've applied a finish that's not too smooth to begin with.

Most people who attempt to apply a polyurethane finish wood eventually resign themselves to sub-standard results, all for lack of one tiny piece of information. But a rough, ho-hum wood finishing outcome isn't certain when you understand how to do power buffing. It works flawlessly on all flat wooden surfaces, using the ubiquitous random orbit sander power tool. I'm not talking about using this sander for sanding, but rather for buffing a finish that you've already implemented.

How To Buff Polyurethane Finishes

You can power-buff all kinds of finishes – wood, metal, and even car bodies. When you get to the bottom of this article, check out my video on how I used buffing techniques to eliminate scuffs and scratches on my vehicles. In this article, I'll show you how it applies here to polyurethane wood surfaces — either oil-based or waterbased. Buffing can transform an average wood surface into one that's smooth as glass and very inviting to the touch. And the work takes just a few minutes. Click the window above to watch an overview of the power buffing process.

Before you do anything else on an original project, read and understand all the steps below.

Polyurethane Finish Tip#1: Start With A Thick Coating

The primary thing to understand is the need, to begin with, a thick polyurethane finish film to assure that you don't buff right through bare wood. That's not to say you should apply each coat thickly. Four regular coats of urethane applied one over the other is a good starting point. Sand lightly with 240-grit sandpaper between coats, then let the last coat dry for at least 24 hours. This is standard practice with any wood finishing job and is nothing out of the ordinary. That said, sanding bare wood beforehand to create a smooth base is key. 

Although buffing makes any urethane look and feels like glass, it might as well use a formulation that's as easy as possible to succeed with. 

Tip 2: Level The Surface Of The Polyurethane

Video Feature

Have you ever contemplated using waterbased stains? These are different than waterbased urethane.

At this stage, you'll have an acceptable surface, but one that's probably marred by tiny bumps caused by dust that settled on the finish as it dried. This is why leveling is the pre-buffing step required next. Start with one of the old pieces of the 240-grit sandpaper you used to sand between coats earlier, then wrap it around a block of Styrofoam and rub the wood surface lightly in the same direction as the grain. It only takes a few strokes to remove the dust bumps, so don't overdo it. Also, be sure to avoid fresh sandpaper for this job because it cuts too aggressively. You don't want to go right through the finish to bare wood. Like I said, use a piece of old 240-grit sandpaper left over from the sanding you did between coats of urethane.

After just a few strokes, you'll find that the surface feels noticeably softer right after de-bumping, though the sheen will be irregular to the eye. It won't be very interesting where the sandpaper did most of its work and shinier where it did less. This is normal. As long as the surface feels perfectly smooth, it's time to move on to the next step.

Tip 3: Power Buffing The Levelled Surface

Now comes the fun. It's time to power buff. Grab your random orbit sander tool and a piece of superfine 3M rubbing paper. This is a thick, non-woven, synthetic abrasive material accessible at woodworking outlets and better hardware stores. It comes in different abrasive ratings, and the superfine type is what you need (it's usually white in color). Cut a 6-inch x 6-inch piece, place it on your project, then put your sander on top. 

Turn on the power. 

As the oscillations and rotations of the tool are transmitted to the pad and the wood, it buffs the surface, removing tiny imperfections while leveling out the sheen beautifully. Work over the whole area evenly and slowly in a grid pattern. A bright light reflecting off the surface at a shallow angle is the best way to highlight areas that need more further work. The more you polish, the shinier the results.

You won't be able to get a sander into every nook and cranny, and that's why you should prefinish parts as often as possible before assembly. 

You can also extend the reach of the buffing treatment using the rubbing pad by hand. You'll find that the process also works on curved surfaces and trim if you use #0000 steel wool. This ultra-fine abrasive is excellent for buffing, but there's a danger. Even though it's metal, fine steel wool can catch fire and burn quickly. Store it in a tightly-sealed metal can for safety. Finish up with a coat of paste wax, also buffed out under power, and you'll have the smoothest possible finish that can be put on wood. You won't be able to resist running your fingers over it.

VIDEO TRANSCRIPT: One of the largest challenges of woodworking is finishing.

It's sometimes a lot easier to build a good project until you get to the finishing part, and that's where disappointment often sets in. This is especially true if you're working in a home shop and you're applying a polyurethane finish with a brush. I want to show you a technique here that will enable you to produce glass-smooth finishes without spray equipment, just using an ordinary brush and polyurethane finish. Now you need to start with a finish of adequate thickness, so that would be at least three layers of polyurethane, and preferably four. The problem at this stage is that your surface is probably going to have little bumps on it from dust bits that have settled out from the air. There may be some brush strokes too, and these are the things that would make the finish ugly. These are the things that I'm going to show you how to remove after the fact.

It all comes down to the right kind of abrasion. So what you want to begin with is a piece of fine sandpaper. This is 320 grit, and it's wrapped around a bit of foam. This could be Styrofoam. This is a little squishier than Styrofoam. You don't want to wrap it around a wooden block. You want something with a little bit of resilience, but you don't want to use the sandpaper by hand. This sample has four coats of waterbased urethane, and the first step involves knocking off the dust bumps. So, you're just drawing this back and forth across the surface.

You're not trying to extract significant amounts of polyurethane, to knock off those little high spots. You want to knock off the mountains, and you're going to know if you've done that adequately with your fingertips. A little bit of movement of this sanding block with paper on it will yield a much softer finish. You'll feel the difference instantly. It's going to be smooth, but it's not going to have an even sheen. Where more abrasion happened, it's going to be dull; and where less abrasion happened, it's going to be shinier.

Further refining the surface is what happens next, and that's where something like this comes in. This is a 3M rubbing pad, so it's non-woven. This is the light grit, and you want to use this, believe it or not, in conjunction with a random orbit sander with no abrasive disc on it. So, the sander causes the rubbing pad to move and polishes the surface. Now, if you want a matte polyurethane coating or something with just a little bit of gloss to it, then all you need to use is this fine pad. It'll smoothen things out and give you just the tiniest little bit of sheen. If you want something shinier, you will accompany this up with the superfine pad used in the same way.

This is what it looks like. It's really pretty simple. You can turn the speed of your sander down a little bit, at least at the beginning until you get the hang of it. I'll just switch on and start the buffing. Now this is a very flat sheen, so you're not going to see some reflections off of it, but it is extremely smooth. It just feels like a piece of glass, and it didn't start off that way. Now if you want it a little bit shinier, you can continue with the power buffing using this ultrafine pad. Now it feels about the same, but you can see some shinier reflections there. It can get even shinier if you buff more. You'd have quite a bit of control over the level of sheen that you can achieve.

Now not every woodworking situation is as nice and flat and open as this sample piece I'm showing you here now, but the same process can be used on any kind of shape or profile. You can start with the knocking off of the dust bumps, and the only difference is that you don't use the random orbit sander for buffing. You just do all the work by hand, and these are flexible enough that they can go around contours and along the edges of panels where they meet stiles and rails, so you can get this kind of result on any surface you might be dealing with.

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