The primary goal when handling woodwork is to deliver a protected and durable surface. But sometimes, one must apply a wood finish to preserve the lumber’s integrity.
In addition, you may have to use multiple wood formulas to guarantee the desired outcome.
However, first things first: it is essential to learn which finishes to combine and how. So, here is a detailed account answering the question: Can You Polyurethane Over Shellac?
It is not advisable to Polyurethane over Shellac. Besides, Amber Shellac is waxy, resulting in a flaking finish.
It also delivers white marks after contacting water splatters. Thus, you’ll need to strip off the Shellac and apply the polyurethane coat.
Fortunately, we have shellac finish types that accommodate polyurethane finishes.
As a result, you can still coat Shellac with Polyurethane. Only use the appropriate products.
This article gives more insight into the polyurethanes and shellac formulas.
It also highlights their pros and cons and how best to combine them for a long-lasting finish.
Table of Contents
What Is Polyurethane?
Polyurethane is a solid varnish that creates a water-impervious finish when dry.
Further, the resulting surface is scratch and solvent-resistant, assuring maximum protection.
Unlike conventional varnishes, Polyurethane has microscopic resin molecule chains that bond tightly with each other.
Thus, you get a sturdier and more lasting finish.
Although a polyurethane coating delivers superior wood and metal protection, it is not an ideal finish coat.
The formula is an artificial polymer and does not penetrate the wood, like Shellac and Lacquer.
However, Polyurethane is still more impact resistant.
In addition, the coating levels out well on surfaces and adheres to any previous finish. It is also less likely to chip under heavy use and traffic.
The formula’s enhanced impact and chemical resistance make it an effective automotive product.
However, please be careful during applications as the product does not flow effortlessly from the spray gun.
Also, polyurethane’s ingredients are toxic, requiring you to get protective clothing, eyewear, and a respirator.
Manufacturers engineer the polyurethane polymer to deliver superior chemical resistance to natural polymers.
Therefore, the coating is less susceptible to discoloration and spotting than other coatings.
In addition, it is a better alternative to lacquer for bars and countertops, where spills are frequent.
Polyurethane is a liquid plastic and cures into a glossy smooth finish. Further, it is available in two types: Oil-based and water-based Polyurethane.
Types of Polyurethane
The two main types of polyurethane are:
This product has a strong odor, a slower drying time, and an amber tint. You can also use it outdoors and on items experiencing more wear and tear.
Oil-based Polyurethane is more durable and heat resistant than the water-based version.
The formula features a minimum odor, cures into a clear coat, and dries very quickly. It is also handy for multiple indoor applications.
However, water-resistant Polyurethane is unsuitable for workpieces exposed to natural weathering or heat.
Remember, the polyurethane base does not affect the sheen level but influences the color.
For example, while water-based formulas do not feature color issues, oil-based Polyurethane turns yellow over time.
Darker woods may not reveal the yellowing. Moreover, some lumber types become more appealing with the warming effect.
But oil-based Polyurethane can eventually ruin lighter-colored wood types. Hence, use the most suitable finish for your workpiece.
In addition, the formula’s base also influences its durability. For example, an oil-based finish is more durable than water-based versions.
It cures within the wood and works best for kitchens, worktables, dining rooms, and flooring.
Further, you must apply more water-based polyurethane coats to deliver long-lasting.
But still, the formula collapses under heat and certain chemicals. Thus, it is a poor choice for furniture and floors.
Fortunately, we have a water-based, oil-modified polyurethane version. It cures into a durable, amber-toned surface.
The product also has a lower toxicity level and cleans up with water and soap.
Like other finishes, oil-based and water-based Polyurethane comes in various sheens. They include matte or flat, satin, semi-gloss, and high gloss.
- Matte or Flat Finish
A matte finish is flat and thus the least reflective. Besides, it features the lowest luster in the spectrum.
The surface has no reflected light. So, it projects a leveled or flat appearance, working perfectly on hardwood flooring.
Matte finishes conceal scratches, dirt, and scuffs, meaning you will not quickly notice lumber flaws and imperfections.
Some woodworkers love a matte appearance, while others find it drab and dull. Thus, it depends on your aesthetic choices and preferences.
The sheen delivers a natural wood grain look and feel. In addition, it is in rustic oak color, camouflaging marks and blemishes.
Also, homeowners prefer matte finishes for functional and practical reasons.
For instance, the finish gives hardwood floors decent traction, minimizing the slippery risk.
Furthermore, it allows pets, toddlers, and the elderly to move around quickly and safely.
- Satin Finish
A satin surface is a popular choice among the existing finishing types. Moreover, it also works magic for hardwood flooring.
The finish is midway, leaning towards a low shine level. It also features enough luster and shies away from too much gloss.
Thus, you will enjoy the benefits of glossy and low-luster matte finishes.
Like matte finishes, satin hides the lumber’s imperfections. But it is clear enough to accentuate the beautiful wood grain.
Besides, smudges, pet scratches, and footprints go unnoticed on satin hardwood floors. Yet, they do not look cloudy like matte surfaces.
A satin finish is easier to maintain and helps keep the floor’s natural appearance.
In addition, the less shine makes it perfect for homes in harsh weather conditions and high moisture regions.
- Semi-Gloss Finish
A semi-gloss surface is also mid-way but appears shinier. In addition, it effectively enhances the wood’s beauty.
Homeowners choose this finish when looking for a shiny appearance. Hence, you will find it in cabinetry and other lumber furniture.
However, there is a caveat. A semi-gloss surface needs regular maintenance and upkeep as the lumber imperfections are easily visible.
- High-Gloss Finish
This finish has the highest sheen level and, thus, the most reflective.
Further, it is eye-catching and works best on exotic hardwood since it emphasizes the natural grain.
You can also use the product for decorative wood carvings, tables, balustrades, and chairs for interior decor.
But remember, a high gloss finish is best for low-traffic areas as it wears and tears more quickly.
In addition, streaks, pet hair, dirt, dents, water marks, dust, and dings are readily visible. Therefore, having a frequent maintenance routine is advisable.
High gloss finishes are excellent for interior wood decor. They project an upscale home decoration level, especially when the wood grain is a focal point on the workpiece.
Sometimes, woodworkers wonder which polyurethane finish delivers the most durable outcome.
But generally, Polyurethane’s superior qualities do not depend on the luster or sheen level. Instead, your result will bank on whether the formula is water or oil based.
Nevertheless, oil-based Polyurethane is more durable than its water-based counterpart regardless of the finish.
What Is Shellac?
Someone discovered years ago, sometime in the 1590s, that if this resin could protect the insect’s larvae, it could preserve the wood.
As a result, the product’s use expanded to include dyes and later became a shellac ingredient.
Shellac comes from the lac bugs of Southeastern Asia. These organisms secrete a natural resin that undergoes processing to deliver a wood finish.
The manufacturer dries the formula and processes it into flakes. Also, they dissolve these flakes in alcohol and create liquid Shellac.
Shellac is an excellent finish on wood workpieces. In addition, you can have it in your medicine cabinet as pharmaceutical companies use it to coat tables.
Further, cosmetic companies use the compound to manufacture hair spray.
The tree where the lac originates from determines its color. Besides, Shellac’s natural hues range from dark brown, yellow, and orange to dark garnet.
Orange or amber Shellac adds richness to mahogany and walnut.
Tinting shellac with any color is possible. Furthermore, this aspect is handy when you want to repair a furniture piece or match an existing color.
All shellac finishes deliver a glossy sheen. In addition, the formula imparts a deep color to the wood and highlights its natural beauty.
However, Shellac is not durable. It easily collapses and dissolves in alcohol and water.
Also, white rings are a problem because you cannot apply the product to very humid regions. The humidity turns the finish white.
Shellac finishes absorb water and turn white or hazy over time. Even worse, although repairs are easy frequent retouching is mandatory.
The product is soft after drying. Therefore, waxing is almost essential to preserve the surface from elements.
Nevertheless, you can comfortably use the product on decorative pieces. Only ensure that the project does not have to withstand hard wear and tear.
Shellac comes in two colors: orange and white. But your choice depends on the furniture’s wood type.
White Shellac comes in handy for light woods. It also needs thinning with denatured alcohol.
In addition, you can tint it with an alcohol-soluble aniline solution, which comes in multiple colors.
On the other hand, orange shellac gives the lumber an amber color. Moreover, it works best on dark wood and is especially attractive on teak, walnut, and mahogany wood.
Shellac also comes in several concentrations or cuts. And the most common category is a four-pound cut.
You can use the product for multiple purposes:
- Use Shellac to seal and polish wooden surfaces. It is available in white and orange flakes, thus accommodating different project needs.
- You can have white Shellac as a sealer. However, a concentrated shellac and alcohol solution delivers a durable coating.
- Orange Shellac is perfect for lumber polishing and gives the surface an amber hue.
How to Apply Polyurethane Over Shellac
There are multiple strategies to adopt when applying Polyurethane over Shellac. You can choose to wipe, brush, or spray the formula and still expect a perfect outcome.
However, each method has its benefits and drawbacks. Therefore, choose the one that guarantees a good finish.
Brush On Technique
This method is among the most popular polyurethane application strategies. It works best for flat surfaces where durability is a priority.
Furthermore, it is straightforward and gives you more control over the amount to apply.
However, you risk having visible brush marks on the cured surface.
So, consider a natural bristle paintbrush for the project and work the formula in long, uniform strokes.
Wiping on Polyurethane is a famous alternative for contoured workpieces. It also works best when you do not want to see brushing drips.
Spraying Polyurethane is among the quickest and easiest ways to deliver a smooth, uniform coat.
Further, you will get a successful outcome even on hard-to-reach surfaces.
However, the method is challenging as you risk over-spraying the formula. Thus, please be careful and patient during the process.
Also, it is advisable to consider the Shellac type before applying the polyurethane finish.
Polyurethane Over Waxed Shellac
Here, please avoid applying Polyurethane over waxed Shellac. The formula will not stick to your surface, resulting in a failed project.
Unfortunately, regular Shellac tends to be waxed. Therefore, melt the topcoat over the wax before adding Polyurethane.
Besides, Polyurethane cannot blend or mix with something. So, it will not stick to the waxed Shellac.
Polyurethane Over De-Waxed Shellac
Polyurethane adheres to dewaxed Shellac regardless of being oil-based or water-based.
In addition, the finish seeks physical adhesion, and dewaxed shellac sticks physically with any topcoat.
Also, dewaxed Shellac is perfect for coatings between polyurethane and stain finishes. This way, you get a stronger bond.
Hence, consider applying Polyurethane over dewaxed Shellac if you want a durable and polished-looking surface.
Let’s now look at a step-by-step procedure for applying Polyurethane over Shellac.
Dilute Shellac With Alcohol
Mix the shellac formula with alcohol before the application. Also, calculate the required alcohol and shellac amount based on the wood’s dimensions.
Brush the Solution
Use a hairy brush to apply the formula onto the lumber.
Further, dip the accessory into the mixture. Then, brush back and forth until you get complete coverage.
Sand the Workpiece
Sand the surface to remove oil, dirt, and dust that may compromise a smooth result. Use the appropriate sandpaper grit for a flawless surface.
Apply the Polyurethane Coat
Apply a polyurethane layer with a clean cloth or paintbrush.
A water-based formula will not need much time, as two hours are usually enough. On the other hand, an oil-based solution needs more time to cure, say around 48 hours.
It is advisable to wait for the first coat to dry before adding subsequent ones. Next, repeat the previous two steps and apply the second polyurethane coat.
Finally, you need three to four layers to deliver a durable workpiece and a rich color.
Watch the Video Below for More:
Can You Put Shellac Over Polyurethane?
You can put Shellac over Polyurethane. But please consider the wood type before application.
Besides, while some polyurethane types do not adhere well to shellac surfaces, waterborne versions do just fine.
So, consider oil-based Polyurethane for minimized problems.
Further, resinous or oily Polyurethane creates bonding issues with other finishes.
Hence, always use a non-abrasive product when applying Shellac over a polyurethane surface.
Shellac is more durable than most finishes. And you can apply it over Polyurethane without affecting its integrity.
It also retains its scratch resistance and flexibility.
However, please clean the surface thoroughly before applying Shellac. An excellent strategy to adopt is using sandpaper to prepare the workpiece.
Moreover, choose a water-based formula as it cures faster. Then, let the first coat dry properly before adding the next, and sand the finish when necessary.
Lastly, please note you’ll need two to four polyurethane coats to deliver the desired outcome.
How to Apply Shellac Over Polyurethane
You can choose to brush or pad on Shellac, depending on the available accessories and preferred outcome.
Brushing on Shellac
Brushing is the most common technique for applying Shellac. The process needs a fine, natural, or china paintbrush.
Next, apply a two- or three-pound formula cut using long, smooth strokes.
Further, Shellac dries quickly. Thus, take care to avoid blotchy areas and drips during application.
Also, you may not have time to over brush to remove the blemish.
Padding on Shellac
This technique is more engaging than brushing,
First, find a clean white rag or sock and cut a clean medium-weight cotton muslin piece or a lint-free polishing rag.
Ensure you cut them into a 12-inch square. This way, you get an efficient pad for the work.
Next, pour the formula into a squeeze bottle with a fine tip. Then, squeeze a generous shellac amount into the sock.
Please do not ignore the sock, as it is a reservoir assuring complete coverage.
Wrap the muslin piece around the sock and hold the fabric edges behind it. Then, lightly squeeze the pad to allow a small shellac amount to seep through the muslin.
Add a lubricant, such as mineral oil, to the applicator before operation.
The solvent does not affect the wood’s final color or finish. Instead, it prevents the pad from being sticky when applying Shellac.
Thus, keep a small bowl of mineral oil for light dipping.
Quickly ease the applicator on and off the workpiece to prevent blotchy areas. Also, please avoid positioning the pad directly on the lumber and rubbing it.
Work the pad using irregular and gentle patterns rather than only following the wood grain.
This way, you guarantee complete shellac coverage. Besides, feel free to squeeze more formula onto the pad if you need more.
Many shellac users prefer to use a brushing and padding combination.
It involves applying the formula with a brush. Then, immediately smooth the surface with a muslin piece.
In addition, use long, uniform strokes along the wood grain for a better finish.
Completing the Shellac Finish
Lightly sand the workpiece with 400-grit sandpaper after the first shellac coat dries. Then, wipe off the white residue with a tack cloth before adding the second coat.
Repeat the process until you deliver the desired coats. However, three or four shellac layers are enough to guarantee a beautiful, uniform finish.
Shellac results in a high-gloss surface. Further, you can achieve a mirror-like glossy finish with french polishing.
But if you want a less glossy surface satin finish, buff the final layer with non-silicon-based paste wax and oooo steel wood.
Next, lightly wax the formula until you cover the surface and allow the wax to dry.
Finally, wipe the wax off and buff the lumber to a lustrous finish.
Pros and Cons of Polyurethane
Generally, adding a polyurethane coat protects your workpiece, extends its life, and enhances its appearance.
We have numerous benefits of adding a polyurethane topcoat. Here are the top five.
Manufacturers combine polyurethane finishes with epoxy primers to deliver a smooth protective film.
The barrier is virtually impenetrable to environmental elements such as salts, moisture, and ultraviolet light.
Further, polyurethane finishes, combined with an epoxy primer, deliver protection against corrosion.
This aspect is essential in coastal environments, especially when keeping sand and salt from harming the structure.
A polyurethane topcoat also protects projects against chemicals harming steel and concrete.
Even better, it keeps bird droppings, debris, dirt, and harmful bacteria from eating away at the material.
Forgoing the finish means taking costly risks in terms of shortened coating life cycles and increased maintenance expenses.
A proxy primer and polyurethane finish work best on multiple finishes.
You can use it on non-ferrous metals, engineered plastic systems, structural steel, and engineered foam systems.
Aliphatic Polyurethane does not have harmful chemicals. Therefore, you do not have to worry whether it’s an appropriate finish material.
Polyurethane’s versatility is among the primary reasons for the product’s prevalence in the market.
Further, it comes in handy for all construction projects, whether adhesives, coatings, and sealants.
The product’s versatility is also evident in its various finishes. You can get it in pearl, solid, and metallic color finishes across the entire spectrum: from gloss to flat/matte.
Lastly, Polyurethane is easy to apply with a roller, brush, or sprayer.
Polyurethane coatings enhance the substrates’ beauty and natural aesthetics.
Besides, aliphatic Polyurethane comes in solid colors and metallics, making the surface reflect with a mirror finish or look wet.
Transparent polyurethane finishes bring out furniture or cabinetry’s beauty. Hence, they are ideal for interior wood applications.
Moreover, you can use the product on stone. It creates a shiny glaze, giving a deeper reflective appearance that livens the surface.
Polyurethane finishes come in handy in architecture. They improve the cleanability and graffiti resistance of metal and cementitious surfaces.
Safety and Application
Polyurethane comes from natural molecules known as monomers.
Further, the formula comes from the term’ polymer,’ a long chain of repetitive monomers.
This finish emits mild vapors after curing. Therefore, it is safe for people and the environment.
However, please wear appropriate safety equipment, especially after spraying the product.
In addition, ensure you have the skills, knowledge, and proper equipment when using Polyurethane.
Improved Durability & Energy Savings
The excellent weathering protection from these finishes gives the project extended life-cycle service.
In addition, aliphatic polyurethanes have a tightly bound resin structure, making them scratch-resistance.
So, you add multiple years to your workpiece by adding a polyurethane coat.
Moreover, most woodworkers prefer it for various projects, like paneling, handrails, doors, window mullions, metal roofs, signage, and metal stairwells.
The formula also adds infrared heat reflectivity, reducing the surface temperature.
As a result, it prevents injuries caused by hot surfaces and aids in reducing a building’s cooling costs.
However, just like other products, polyurethane finishes have a few drawbacks. It is advisable to go through them before choosing the formula for your work.
These cons include
Frequent Maintenance and Reapplication
Unfortunately, Polyurethane has hygroscopic tendencies, that is, water absorption qualities. Thus, it eventually disintegrates and loses its support quality.
Similarly, polyurethane sealants and adhesives absorb atmospheric moisture, affecting their durability.
You Need Safety Equipment During Application
Although Polyurethane’s odor is not highly noticeable, it is advisable to have a facemask during operation.
The petroleum-based compounds and flame retardant fumes can cause physical problems. Besides, prolonged polyurethane exposure makes people ill.
Health problems associated with the product include allergic reactions, loss of consciousness, blindness, rashes, and difficulty breathing.
Clean and rinse them to avoid severe effects when your skin or eyes come in contact with Polyurethane.
Polyurethane foam produces toxic fumes when burned.
Moreover, some blowing agents in the formula produce greenhouse gases with adverse atmospheric effects.
Some polyurethane foam features non-renewable fossil fuels, adversely affecting the environment.
Finally, please note that although Polyurethane is not as toxic as other compounds, it still harms the environment.
Pros and Cons of Shellac
Shellac, like Polyurethane, has pros and cons. Further, it is prudent to go through them to enhance your decision-making process.
Pros of Shellac are
- The formula is non-toxic, with no fumes or odor. Therefore, it is environmentally friendly.
- It is safe for surfaces used by kids and pets.
- Shellac is easier to handle as you can brush it on or spray it.
- It dries quickly, allowing you to complete your project on time.
- The product delivers a hard, natural-looking finish.
- Repairs and maintenance exercises are easy. You only need to apply a new shellac topcoat when necessary.
- Shellac finishes are available in various colors.
- You can strip the topcoat with alcohol.
- The shellac surface is resistant to ultraviolet rays and does not darken with age.
Further, the cons are as follows.
- Shellac is vulnerable to anything with alcohol, such as cologne or liquor.
- It softens under heat, requiring you to keep it away from hot surfaces.
- The finish deteriorates after sitting in an alcohol mixture for a while.
- Shellac surfaces are not water-resistant. Therefore, they are unsuitable for bathrooms and kitchens.
- Watermarks and humidity give the finish a whitish tinge.
- Shellac is not as durable as other lumber finishes. Thus, it is advisable to coat it with a more robust finish.
Nevertheless, shellac finishes are still an excellent wood product. Do not let these drawbacks dissuade you from using them.
Frequently Asked Questions
Some of the most asked questions are:
Why Should I Not Put Polyurethane Over Amber Shellac?
Generally, many people believe that you should not apply Polyurethane over Amber Shellac.
Besides, even Shellac cans warn about the combination, and the finish is prone to chipping.
But regardless of the belief, bold woodworkers ignore these warnings and use Polyurethane over Amber Shellac.
Another reason to avoid using Polyurethane over Amber Shellac is because of the former’s decreased quality.
Lastly, coating Amber Shellac with three polyurethane layers delivers a cloudy finish.
In addition, the surface can become yellow over time, depending on the product brand.
Is Shellac a Good Wood Finish?
Shellac is an excellent wood finish thanks to its incredible qualities. For instance, it highlights the wood grain and is easy to handle.
Besides, the formula is very versatile, accommodating multiple applications and surfaces.
Shellac finishes enhance the wood’s smoothness. And it seals the surface by creating a moisture barrier.
Furthermore, the product does not deliver a plastic appearance like lacquer or Polyurethane.
Shellac does not discolor or turn yellow over time. It has impressive UV rays resistance, maintaining the workpiece’s integrity.
In addition, you can use it on Mahogany and Walnut workpieces and expect a fine, mellow finish.
The formula also polishes well, and woodworkers associate it with traditional French polish.
Although shellac surfaces are heat-sensitive, they are reasonably durable.
Also, place a trivet or coaster on the workpiece to prevent white rings. Otherwise, you risk leaving white rings on the surface.
Shellac is easy to brush on, and you can also apply it with a cloth when working on cabinets.
Finally, use denatured alcohol to cut the shellac amount for a satisfactory outcome.
Is Shellac Wood Finish Toxic?
Shellac is not toxic. It comes from lac, a resin secreted by an insect.
The formula is 100 percent natural and has FDA approval for use in coating medicines, foods, and cosmetics.
As a result, a shellac surface is appropriate for use on children’s furniture.
Can You Apply Lacquer Over Shellac?
Although Shellac is an excellent sealer, it falls short in water and scratch resistance. Therefore, you’ll need to coat it for guaranteed durability.
Fortunately, you can apply lacquer over the finish. This way, you protect the underneath surface and deliver better quality work.
However, it is advisable to sand the surface smoothly before adding the lacquer coat.
In addition, use dewaxed Shellac when applying lacquer or strip a previously waxed surface.
How to Waterproof Over Shellac
Shellac is a classic product for premodern woodwork and remains a primary finishing option for authentic history lumber furnishing restorations and re-creations.
You can also use it for implements and fixtures.
Unfortunately, the formula falls out of fashion due to its water and alcohol susceptibility. So, you need to coat it with a transparent sealant for added longevity.
The first step is to lay out several old newspaper layers or a drop cloth. This way, you protect the surrounding area from spills.
Next, sand the shellac finish with fine-grit sandpaper on a sanding block. The exercise scuffs up the surface with micro-scratches, creating a rough surface.
As a result, the waterproofing sealant bonds better.
However, please sand lightly to avoid removing the finish or a substantial wood amount.
Wipe the surface with a tack rag to remove sawdust and debris. Then, apply a transparent polyurethane finish using long, even strokes.
Lastly, wait for a few hours before adding subsequent coats.
Can I Apply Polyurethane Over Zinsser Shellac?
Unfortunately, Zinsser Shellac manufacturers do not recommend applying Polyurethane over the product.
But you can do some tests during your DIY escapades and confirm if the strategy works for your project.
Can I Paint Over Shellac?
You can paint Shellac. But please note that its glossy finish does not hold paint well.
So, the project needs extra preparation to deliver a durable outcome. Further, remove the shellac finish before applying the paint.
This way, you keep the paint coat from flaking off the workpiece later.
How Long Does Shellac Need to Dry Before I Apply Polyurethane?
Unlike a polyurethane finish which needs 24 hours to dry thoroughly, Shellac does not need much time.
Besides, it only requires one hour before screening or sanding. And the second Shellac coat should cure within two to three hours.
However, remember that Shellac is less durable and vulnerable to scratches than Polyurethane.
Various sources differ on whether you can apply Polyurethane over Shellac surfaces.
Moreover, some reputable wood finishers and several Shellac manufacturers discourage coating shellac with Polyurethane.
But despite the seemingly ordinary rule, woodworkers are curious whether they can bend the directive.
So, check out the discussion on:
Can You Polyurethane Over Shellac?
Applying Polyurethane over Shellac is not advisable. The latter has wax qualities that compromise adhesion.
However, all hope is not lost. You can deliver a successful outcome with the correct application techniques and supplies.
For instance, an oil-based polyurethane formula guarantees a more durable surface than its water-based counterpart.