Polyurethane is a famous coating that protects lumber surfaces from scratches and water damage. It also improves your furniture by delivering a smooth, glossy finish.
The formula is easy to apply with various accessories, whether spray or brush. But although each applicant may deliver a satisfactory result, choosing the most suitable one is advisable.
In addition, professionals recommend spraying, meaning you’ll need to thin the product. Therefore, let’s engage in an insightful discussion on How to Thin Polyurethane for Spraying.
The first step is to stir the formula and transfer it into a polyurethane glass jar.
Then, add the recommended thinning medium and stir again for excellent mixing.
Moreover, it is advisable to use the correct thinner.
For instance, water-based Polyurethane thins with denatured alcohol or water.
The oil-based version works best with lacquer thinner, mineral spirits, and naphtha.
However, please avoid over-thinning the formula. And consider a one-to-four ratio for mineral spirit and Polyurethane, respectively.
Thinning Polyurethane is an essential exercise before spraying.
Thus, read this article for an in-depth understanding of handling oil and water-based Polyurethane to guarantee expert results.
What Is Polyurethane? And Why Should You Thin It?
Polyurethane consists of two primary chemical compounds: urethane and polymers.
Further, the manufacturer links the polymers by urethane groups, creating a versatile formula.
As a result, the product takes many forms while being safe, stable, and durable.
Unlike multiple potential synthetic compounds, polyurethane products are heat resistant and do not melt when heated.
This quality makes them excellent for applications emitting large energy amounts, like cars and refrigerators.
More specifically, a polyurethane finish is a sturdy varnish with tightly bonded microscopic chains of resin molecules.
Moreover, it cures to deliver a solvent, water, and abrasion-resistant surface.
Also, you will not have to worry about wear and tear from regular use.
Polyurethane formulas are available in two primary types: Oil-based and water-based.
In addition, manufacturers recently introduced a third category, water-based oil-modified Polyurethane.
However, although all polyurethane finishes deliver a smooth and gorgeous finish, using the wrong product compromises the outcome.
In addition, while oil-based and water-based Polyurethane give the same result, they feature unique attributes.
Here are some comparisons to help in your decision-making.
It is prudent to know how various polyurethane finishes appear. For example, oil-based formulas look yellowish, whereas water-based products are milky.
Further, the oil-based Polyurethane features an amber hue and darkens over time, whereas its water-based counterpart dries crystal clear and remains transparent.
Thankfully, these colors are neither a good nor a bad aspect. It boils down to personal preferences.
Choose an oil-based finish for a darker and more lively-looking hue or a water-based product to accentuate the lumber’s natural beauty.
Oil-based Polyurethane needs five to 12 hours before you can add a second and third coat.
On the other hand, the water-based version requires only two hours or less in a favorable environment.
Volatile Organic Compounds and Toxicity
Unfortunately, spray polyurethane features isocyanates and emits VOCs, making them toxic.
Worse still, this toxicity heightens during spraying. Therefore, it is wise to work in a well-ventilated area or outdoors.
Although both polyurethane versions emit VOCs, the fumes are more significant in oil-based finishes.
These products have larger chemical quantities, requiring you to handle them carefully.
In addition, wear protective gear during the application, and please keep the formula away from children, pets, and anyone with respiratory challenges.
Another consideration when working with Polyurethane is how easy or challenging it is to clean your tools.
For instance, you can quickly thin a water-based formula and clean applicants with water and a gun-cleaning solvent.
Thus, cleaning up messes during the application is cheap and helps you save time later.
Conversely, oil-based Polyurethane needs mineral spirits and solvents during thinning and cleaning. This process needs considerably more time and is quite engaging.
Various woodworkers have different reasons for thinning Polyurethane.
For instance, some assume that thinning the product with naphtha and other solvents delivers a faster-drying formula.
However, this thought is not necessarily true. The thinner evaporates faster in oil-based Polyurethane, leading to a slow crosslinking process.
Crosslinking activity refers to a reaction between oxygen molecules and the formula.
Moreover, adding more thinning solvents to Polyurethane does not guarantee that the second stage will complete faster. The oxygen reaction takes the same duration.
Applying thin polyurethane coats guarantees a faster drying duration, but you’ll need more layers for a long-lasting finish.
Hence, thinning Polyurethane does not fasten the formula application procedure.
On the other hand, other woodworkers thin Polyurethane because they prefer how it levels on the surface. The formula also quickly builds up gradually in slow, thin coats.
We also have woodworkers who love Polyurethane’s appearance after thinning.
Furthermore, a thinner formula gives the user more control during the application, leading to a better finish.
Lastly, laying thin layers helps you see when you need to stop. It is easier to notice when the polyurethane layer is thick enough.
This way, you deliver adequate surface protection while preventing a plastic appearance.
What Do You Use to Thin Polyurethane
Woodworkers can use various thinning strategies and mediums to wipe varnish or thin Polyurethane.
These products include denatured alcohol, turpentine, mineral spirits, water, and paint thinner.
Although this formula is excellent for thinning Polyurethane, it is best suited for diluting water-based formulas.
Further, like water, the product does not mix well with oil-based finishes and would only ruin the outcome.
Work in a well-ventilated area when working with denatured alcohol. The solvent features strong fumes and irritates the skin.
In addition, thin Polyurethane with the exact denatured alcohol amount you would with water.
Utilize this mild solvent for oil-based Polyurethane and varnishes. Besides, mineral spirits are petroleum distillates and contain oily resins from trees.
The mineral spirits quantity used depends on how thin you want the formula.
In addition, although the product has a low odor, operating in a well-ventilated space and wearing gloves is advisable.
Turpentine is suitable for thinning oil-based Polyurethane. However, most woodworkers use it for thinning oil-based polyurethane paint.
Use the same quantity as mineral spirits to dilute oil-based Polyurethane.
Also, please note that turpentine has a heavy scent with a toxic smell that does not dissipate quickly.
As a result, work outdoors, and wear long sleeves, gloves, and a respirator mask. Otherwise, overexposure to these fumes triggers skin irritation and headaches.
Water only works for water-based Polyurethane, not its oil-based counterpart.
The primary reason is that water-based formulas use water as their base and carrier for product particles.
Therefore, water does not affect the formula’s viscosity and texture. In addition, it is the safest thinning alternative, just like the water-based product.
Lastly, paint thinner is another medium to thin Polyurethane. Further, we have an oil-based and water-based variety to accommodate multiple applications.
So, you only need to match the paint thinner with the polyurethane base.
Simply put: utilize an oil-based thinner for oil-based Polyurethane and a water-based one for a water-based product.
Also, please note that using the wrong paint thinner leads to a failed polyurethane job. Thus, gather the correct supplies.
How to Thin Oil Based Polyurethane
The project needs naphtha, mineral spirits, or lacquer thinner as the polyurethane thinning agent.
In addition, you require a glass jar, Polyurethane, clean rags, a spray gun, and a clean stick for mixing.
Next, follow the steps below:
Clean Glass Jar
Using a glass jar is better than a paint bucket, as you can see the medium’s reaction clearly. It helps you mix Polyurethane and mineral spirits in the correct ratio.
Further, cleaning the glass jar is advisable as it ensures no contaminants compromise the process.
Thus, clean and eliminate paint and dust from the glass jar using warm water and soap.
In addition, you can remove stubborn stains and residues by wiping them with alcohol.
Please avoid cutting the spray can when using Polyurethane in a spray container.
Moreover, manufacturers design the product as thin Polyurethane. Hence, you do not need additional thinning.
Conversely, manufacturers recommend thinning Polyurethane that does not come in spray cans. Therefore, open the container and pour enough formula into the glass jar.
Add Mineral Spirits or Paint Thinner
The next step is to add mineral spirits or paint thinner to the glass jar. Also, maintain a one-to-four ratio: one part mineral spirit and four parts polyurethane.
A measuring cup can deliver the perfect medium and polyurethane ratio. Pour half a cup of mineral spirit or paint thinner into one polyurethane gallon.
The goal is to dilute the Polyurethane as much as possible without compromising its efficacy. Thus, add the thinning agent according to the application type.
Stir the Mixture
Take the clean stirring stick and stir the mineral spirit and polyurethane mixture for ten minutes.
Further, maintain a uniform pressure on the stick and adhere to the figure eight stirring motion during mixing.
Otherwise, stirring too quickly creates bubbles in the mixture.
In addition, these bubbles are a huge challenge as they never leave even after polyurethane application.
Moreover, stirring eliminates air bubbles and initiates the polyurethane thinning process.
Test the Polyurethane
Test the thinned polyurethane formula with a spray gun on a wood piece or cardboard. Then, wait until the formula dries to observe its appearance.
You have successfully thinned the finish if the resulting polyurethane coat has no bubbles, imperfections, or color variations.
However, adding some polyurethane to the mixture is okay if you find it too thin. Stir the formula and test it again.
Also, add mineral spirits if the Polyurethane is still too rough.
How to Thin Water Based Polyurethane
This project requires denatured alcohol and water. Further, the solvent needed depends on the polyurethane brand and application technique.
Other supplies include a spray gun, a clean mixing stick, and a glass jar.
Then, follow the thinning procedure below.
Clean Glass Jar
Cleaning the glass jar is essential as it houses the thinner and Polyurethane during the reaction. Besides, you need a clean mixing environment with zero interference.
So, clean the jar using warm water and soap to remove paint and dust. This way, you guarantee a successful result.
Water-based Polyurethane in containers other than spray cans requires thinning before spraying. Thus, open the can and pour a sufficient polyurethane amount.
Also, please ensure that the glass jar has enough space to house polyurethane and water/denatured alcohol.
Add Water or Denatured Alcohol
Add the chosen thinning agent, water, or denatured alcohol in small increments until you get the desired level.
Moreover, add the medium about two to three percent of the total volume. For instance, add 0.4 water ounces to the 20 fluid polyurethane ounces.
Generally, manufacturers state the water amount to add to Polyurethane on the package.
In addition, they recommend that the formula is as light as possible to deliver the best outcome.
Thus, please follow the product directives and avoid instantly adding 90% polyurethane to ten percent water. Otherwise, you’ll over-thin the formula.
Furthermore, adding water slowly while gradually increasing the amount until it meets the best thinning volume is the best practice.
Stir the Mixture
Take the clean stirring stick and gently stir the water and polyurethane mixture. Spend about ten minutes and avoid moving in a hurry lest you introduce bubbles in the formula.
In addition, please avoid shaking the mixture too much during stirring.
Test the Polyurethane
Finally, test the thinned formula on a lumber piece or cardboard. Add a small polyurethane amount to the spray gun and apply it to a scrap piece.
Observe the result: Check whether the Polyurethane has a consistent finish with no blemishes, color variations, or bubbles.
Finally, add Polyurethane if the mixture is too thin and repeat the test or some denatured alcohol or water if the Polyurethane is too rough.
How to Spray Polyurethane
Ideally, spraying Polyurethane is the quickest application strategy. Further, the finish dries faster and guarantees a more uniform coat.
This next session gives you the correct procedure to follow when spraying Polyurethane. However, remember that the finish is flammable.
Therefore, please avoid applying it near open flames or direct sunlight.
First, you need the following supplies:
- 220-grit sandpaper
- Mesh filter
- Mineral spirits or paint thinner
- Spray gun or paint sprayer
- Tack cloth
- Drop cloth
- Vacuum cleaner
Then, check out the steps below.
Wear Protective Gear
Covering yourself fully to remain safe from Polyurethane is essential. The formula has Volatile Organic Compounds and isocyanates, which are toxic.
Even worse, they can accidentally enter your nose, eye, and mouth, causing health hazards.
Generally, the formula’s toxins and fumes cause problems during spraying. Thus, please avoid using a sprayer if you have respiratory conditions or are asthmatic.
Further, consult a doctor before handling the product.
The four primary items to have when spraying Polyurethane are gloves, goggles, an overall, and a respirator.
You can wear long clothing instead of an overall when applying water-based Polyurethane.
Prepare the Work Area
Unfortunately, spraying Polyurethane is challenging to control. Hence, it will accidentally spill on other wooden surfaces and surrounding areas.
As a result, use a drop cloth or painter’s tart to protect other items in the workshop.
In addition, open the doors and windows when working indoors to facilitate proper ventilation.
You can switch on the fan but ensure it does not blow in your direction.
Prepare the Formula
Preparing Polyurethane is mandatory. Otherwise, it will not finish properly, compromising the final result.
Luckily, the preparation procedure is not something out of this world, but pretty straightforward.
Stir the Polyurethane
Although shaking spray paint does not pose a bubbling risk, it is not ideal for Polyurethane.
Shaking the latter causes bubble trouble, leading to unnecessary turbulence during operation.
On the other hand, stirring Polyurethane mixes flattening agents and solids. Moreover, flattening mediums determine the final sheen.
Therefore, you are sure of a more consistent and solid color.
Filter the Finish Using a Pantyhose or a Mesh Filter
Thin the Polyurethane or pour it directly into the sprayer, depending on the product version.
But thinning the formula guarantees a smoother and more consistent finish. Hence, set aside some time for it.
Please use the correct thinner for your polyurethane type. For instance, use mineral spirits for oil-based formulas and water for water-based ones.
Also, follow the manufacturer’s instructions on the can.
Wipe Away all the Dust
Sanding the surface is prudent before you apply Polyurethane. The exercise roughens the material and facilitates better adhesion.
It also removes blemishes that would compromise a professional outcome.
Afterward, use a tack cloth or vacuum cleaner to remove residual dust after sanding.
Also, remember that although spraying eliminates the bubbling risk, you can still get dust nibs. Thus, take your time to clean the surface.
Clean dust sources around you. Otherwise, the fan or the wind will blow it on your work and ruin the outcome.
Test the Sprayer
Like other motorized devices, a paint sprayer is unpredictable. Besides, it splutters when you spray the first batch.
Hence, test the tool on a random surface before working on the workpiece.
In addition, check whether you get a smooth, even flow, and test it on a wooden surface if handling a lumber project.
This exercise is also crucial as you may or may not like the finish. Therefore, you can make the necessary changes before coating the workpiece.
For instance, oil-based Polyurethane adds an amber tint to the surface. So, feel free to switch to a water-based formula if you want to change how it appears.
However, although water-based Polyurethane dries crystal clear, testing it out is advisable.
The finish still causes yellowing and discoloration on white-painted surfaces.
Spray the First Coat of Polyurethane
Hold the canister ten to 12 inches away from the workpiece. Then, spray the first polyurethane coat quickly to avoid over-spraying one spot.
Moreover, maintain a stiff wrist and apply the formula in continuous, sweeping motions, ensuring you stay in one area for a short time.
Otherwise, you risk delivering drip and runs, especially when coating a vertical surface.
Always finish spraying the workpiece in one motion. Also, utilize thin coats as they dry faster and are easier to evaluate.
We have three spray patterns on polyurethane sprayers to accommodate various surfaces. They include
Horizontal Spray. This type is applicable when spraying fronts, doors, and cabinet sides.
It works best on vertical surfaces, and the patterns move from left to right or right to left.
Vertical Spray. This strategy works best on flat or horizontal surfaces like tables. However, the manufacturer designs it to move vertically and horizontally.
Wait for the Surface to Dry, Then Sand
Typically, Polyurethane needs approximately two to four hours to cure before adding a new coat. Then, remove dust nibs, runs, and uneven spots with 220-grit sandpaper.
Sand the surface gently, following the wood grain. But avoid going too deep lest you scratch the surface.
You only need enough pressure to even the wood and roughen it for better adherence.
Remove the Sanding Dust Again
Bring out your tack cloth or vacuum cleaner after sanding. Also, be patient during this process, as the surface will have dust particles, which the spray will blowback.
Apply Another Polyurethane Coat
Spray another coat just as you did the previous one. However, test it on unfinished lumber surfaces to confirm the sprayer is working correctly.
Next, repeat steps six to nine until you get the desired finish. And remember that you’ll need three to four coats for a smooth surface.
Let the Surface Cure
Allow the polyurethane coating to cure appropriately after application. Further, please avoid placing heavy objects on the workpiece before it cures.
The average waiting duration is four weeks for oil-based Polyurethane and three weeks for its water-based counterpart.
Here’s a Video On How to Spray Polyurethane:
Tips to Consider When Using a Sprayer
Spraying Polyurethane is pretty straightforward, but it is challenging if you do not know what to check out. Here are some guidelines when handling the formula.
- Watch out for drips and runs when applying Polyurethane on vertical surfaces.
- Also, spray thin coats and only go over a spot once it dries completely. Then, use a sharp razor blade to remove runs gently.
- Always spray the formula in a clear light and observe the workpiece from various angles. This way, you’ll not worry about over-spraying or missing an area.
- Spray the surface when working on plain pieces like tabletops. It helps cover all areas quickly and easily.
- On the other hand, use a brush for edgy and curvy projects like table legs. It delivers better coverage. Remember, filling holes and cracks with a sprayer requires you to over-spray the spot, causing uneven coating.
Recommended Sprayers for Applying Polyurethane
YATTICH Paint Sprayer: Best for Oil-Based Polyurethane
This accessory takes versatility to the next level. It is a high-powered spray gun with five copper nozzles, making it perfect for multiple applications.
Furthermore, you can use it with any polyurethane type or for outdoor and indoor applications.
YATTICH sprayer features three spray patterns: horizontal, vertical, and circular. It also has a volume control knob to release less or more formula.
Although oil-based Polyurethane is prone to clogging during spraying, this product has copper nozzles that deliver better spraying output.
Besides, you can clean the tool after use without damaging them.
YATTICH paint sprayer is detachable, making cleaning convenient after every application.
It also traps moisture and dust during the application, a critical requirement when applying oil-based Polyurethane.
Lastly, you will receive a complete kit with a fluid nozzle cleaning needle, a spanner, a lidded pot, a cleaning brush, and a viscosity cup.
These features guarantee optimal operation and a successful outcome.
HomeRight C800971: Best for Water-Based Polyurethane
This unit is light, easy to use, and does not consume much power.
Further, water-based Polyurethane is ideal for extensive projects due to its quick-drying attribute. Thus, using a suitable sprayer is prudent.
HomeRight is a multipurpose paint sprayer suitable for many polyurethane formulas.
In addition, it works best for multiple indoor and outdoor projects, from small cabinets and desks to fences and walls.
The tool runs on 450 W of power, making it perfect for extensive applications. It is also easy to adjust using the volume control knob.
HomeRight’s air cap sprays in three directions: vertical, horizontal, and round. Therefore, you can use it on other formulas, such as milk paint and chalk paint.
In addition, the unit has three brass spray tips, offering better consistency and plastic tips. These tips are also corrosion and wear-resistant, guaranteeing longevity.
However, the spray gun is more challenging to clean than other excellent units. Therefore, you may spend more time and effort during clean up.
What Happens If You Over-Thin Polyurethane?
Over-thinning Polyurethane is a primary risk factor associated with thinning the formula. Worse still, the practice has several consequences.
For example, over-thinning the formula makes the finish too light to apply.
It ruins the product’s tint and compromises the original color, making it pointless to apply the finish.
Another consequence is increasing the dripping and running risk during application. This aspect is a nightmare when coating vertical surfaces like walls and doors.
In addition, overly thin finish coats do not adhere to the workpiece. Therefore, the coat eventually flakes and peels off, causing wastage.
Even worse, sometimes the coat fails within six months of application.
Another potential Polyurethane over-thinning outcome is that the formula losses its water-resistance qualities.
Hence, you predispose the surface to moisture damage; thus, the finish may look dull and blurry.
Finally, strictly follow the manufacturer’s recommended thinning ratios to guarantee a successful application.
However, salvaging the over-thinned formula is possible by adding more Polyurethane. So you do not have to panic after over-thinning the product.
Frequently Asked Questions
Do I Have to Thin the Polyurethane Before Spraying?
Generally, thinning Polyurethane is optional before spraying. But the process enhances a smoother and uniform finish. So, professionals highly recommend it.
However, ensure you purchase the most suitable thinner for your polyurethane type.
Water-based Polyurethane works best with water and denatured alcohol, whereas oil-based formulas need paint thinner or mineral spirits.
Also, test the thinned product on small wooden surfaces. This way, you confirm that it will deliver the desired outcome.
Is Spraying Polyurethane Toxic?
Unfortunately, spraying Polyurethane is toxic. The exercise releases VOCs into the air, posing environmental and health hazards.
Hence, wear safety gear when handling the formula for maximum safety.
Besides, VOCs cause multiple health issues. So, ensure you follow the manufacturer’s application recommendations properly.
On the positive side, Polyurethane’s toxicity ends after drying. Therefore, the workpiece is safe for use once it cures.
Are there Finishes That Don’t Need Thinning?
We have finishes that do not need thinning to deliver complete coverage and a smooth surface. They include hard wax, linseed, and tung oils.
In addition, some Varnishes and oils already include petroleum distillates and mineral spirits. Thus, they are perfect for use without thinning.
Water-based Polyurethane is famous for its low VOC levels, meaning it is not as toxic and hazardous as other formulas.
Moreover, thinning the product is unnecessary, thanks to its innate consistency.
How Much Can I Thin Polyurethane?
Typically, polyurethane thinning ratios depend on the intended application mode, the formula type, and surface size.
Thin the Polyurethane at ten percent for the water-based version and up to 50% for oil-based Polyurethane.
Also, thin it gradually while observing the formula’s consistency and adjusting the ratio accordingly.
However, mix the product with three parts polyurethane to one part thinner if you’ll apply the formula with a paintbrush.
Also, ensure the Polyurethane is always more than the thinning medium, except when working with half Polyurethane and half mineral spirits.
Lastly, pour the thinning solvent into Polyurethane, not vice versa, when diluting the product.
How Do I Thin Water-Based Polyurethane for Wiping?
Transform a water-based formula into a wipe-on by adding ten to 15% water. This quantity makes Polyurethane thin enough for rag application.
But remember, professionals, recommend spraying and brushing for water-based polyurethane application.
Can I Use Fleotrol to Thin Water-Based Polyurethane?
You can thin water-based Polyurethane using Fleotrol.
Besides, although the product is primarily designed for latex paints, it works perfectly with water-based finishes.
Fleotrol enhances the formula’s consistency, self-leveling features, flow, and weather resistance.
How Much Should I Thin Polyurethane for Spraying?
Always thin oil-based Polyurethane by adding one part mineral spirit to four parts of Polyurethane. So the ratio is 1:4 for mineral spirit to Polyurethane.
Conversely, thin water-based Polyurethane by adding water in small increments, usually two to three percent.
Proceed until you reach the optimal consistency. Also, increase the added water level to ten percent of the total volume.
Finally, the Polyurethane to water ratio varies depending on the application type and product brand.
What Happens If I Over-Thin Polyurethane for Spraying?
Over-thinning Polyurethane compromises your furniture’s final finish. Further, the coating needs a sufficient binder and polymer to adhere to the surface.
Therefore, the practice leads to troublesome occurrences such as poor durability, a blurry finish, and susceptibility to water and scratches.
In addition, the finish may adopt a lighter color than intended and even result in blotchiness.
Can Paint Thinner Thin Polyurethane?
Paint thinners can thin Polyurethane for better application. But the product is available in multiple types.
Therefore, check the product label to ensure it is compatible with the polyurethane type.
Paint thinner works magic as long as it’s compatible with the polyurethane finish. So, add it in stages to avoid over-thinning the topcoat.
Furthermore, the formula is very effective, and using too much leaves a watery solution.
Open the polyurethane can and pour the paint thinner slowly. But please do not go crazy here; instead, add a little at a time.
You can always add more later to get the desired consistency.
Next, stir the solution with a clean stirring stick and determine if you need more paint thinner.
Which Is the Best Thinning Technique to Use?
Although we have various thinning agents and techniques, using the correct one is prudent to avoid wasting your Polyurethane.
In addition, add the thinner as carefully as possible.
The best way to thin a formula involves using a clean stirring stick. You can get the accessory from hardware and paint stores.
Also, please avoid shaking the polyurethane container. Otherwise, you will add air bubbles into the mixture, making the finish less smooth.
Hence, slowly pour the thinner in several batches, stirring it using a figure eight motion.
Ensure you scrape thick materials from the can’s sides and bottom. And continue until the Polyurethane has a uniform texture.
Lastly, pay attention during this process to avoid making the Polyurethane too watery.
This occurrence compromises the formula’s efficacy. So, work slowly until you deliver the perfect texture.
Thinning Polyurethane is standard practice for painters and woodworkers.
Besides, it is necessary if you want to deliver smooth and perfect coverage. Otherwise, the finish will be too thick and not dry well, resulting in cracking and peeling.
Unfortunately, please avoid guesswork as much as possible during the process.
Ensure you use the correct polyurethane thinner and in the correct ratio to guarantee a safe and effective operation.
In addition, consider the guide above for an excellent outcome.
How to Thin Polyurethane for Spraying
Generally, thinning Polyurethane is critical to delivering a successful finish. But each product type thins differently.
Always use paint thinner, mineral spirits, and turpentine for oil-based Polyurethane and denatured alcohol or water for the water-based version.
Lastly, adhere to the recommended thinning ratio. Slight alterations with the thinner may cause over-thinning and compromise the finish.