How To Thin Polyurethane? (Step-by-Step Guide)

The technique of diluting polyurethane is popular among those who engage in woodworking and painting.

It is necessary to water down the material to properly coat the surface that needs to be protected with polyurethane.

If the polyurethane is not thinned, it will become too thick and not dry appropriately, which may result in peeling or splitting.

In this article, we will instruct you on how to thin polyurethane in a way that is both secure and efficient. In addition, we will discuss the most effective polyurethane thinner, as well as the appropriate mixing ratio.

Be careful, yet enjoy yourself while working on your creations!

VIDEO: How To Thin Polyurethane?

How to Reduce the Thickness of Polyurethane

When diluting polyurethane, you should begin by stirring the poly and then transferring it into a glass jar. After that, pour in the appropriate medium for thinning. 

Finally, give it one more stir to ensure everything is thoroughly combined. 

To thin water-based polyurethane, either water or alcohol that has been denatured can be used. In addition, you can soften oil-based poly with mineral spirits, paint thinner, or turpentine.

How Much Is Water Needed to Dilute Polyurethane?

The ratios for thinning polyurethane are different depending on the type of polyurethane, the manner of planned application, and the surface’s size. 

Applying polyurethane with a spray gun or paint sprayer, thin the material to a consistency of 10% for water-based poly and up to 50% for oil-based polyurethane. 

Then, gradually dilute it while examining the consistency and changing the proportions according to your preferences.

If, on the other hand, you need to dilute polyurethane with a paintbrush, you should combine the product with one part thin and three parts polyurethane.

Always ensure that there should be more polyurethane than the specific thinner; with the except forms, you must put in half mineral spirits and half polyurethane.

When watering down polyurethane, you should add the thinning agent to the polyurethane rather than doing it the other way around.

To Spray the Polyurethane, Is It Necessary to Dilute It?

 You may achieve a pleasant-looking finish smooth by thinning the polyurethane. However, this is optional in any way.

Most polyurethane spray cans do not need to be thinned because these cans are already intended to contain the least amount of product feasible production process will be simplified as a result. If the polyurethane does not come in a spray can and you are planning to apply it via spraying.

The wood is much more actively sealed with thinned polyurethane, which prevents blotches and streaks from forming.

Regular polyurethane coatings take longer to dry but have fewer texture bumps and are more effective overall when compared to coatings made with thinned polyurethane.

Many solvents, including naphtha, mineral spirit, and others, have a rapid evaporation rate. Therefore, putting a thinner coat of polyurethane will also result in a quicker drying time due to the rapid evaporation.

Rough ordinary polyurethane is notoriously difficult to dry, and its surface is prone to blotchiness and other imperfections.

If you are starting in the wood finishing world, it is best to deal with thin polyurethane to reduce the number of problems you run into.

A significant moisture content can be found in ordinary rough polyurethane. Because of this, the drying rate is high, and they lay on the surface for a significantly extended period until they dry.

How Can I Dilute Oil-Based Polyurethane So That It Can Be Sprayed?

Mineral spirit, naphtha, or lacquer thinner are the three solvents used to thin oil-based polyurethane. They perform the role of a solvent, which allows the coating of polyurethane to be reduced in thickness.

To better understand oil-based polyurethane for spraying, let’s go through each previously discussed process in depth.

Jar made with clean glass.

The glass jar is preferable to paint buckets since the reaction medium can be seen clearly, and you won’t be able to mix polyurethane and mineral spirit in the wrong proportion if you use the paint buckets.

It is vitally crucial to clean a glass jar thoroughly since this is the location where polyurethane and mineral spirit come into contact, and a reaction takes place.

The reaction must occur in an uncluttered space free from any outside influences to get the best results from mineral spirit when used to dilute polyurethane.

Using warm soapy water, wipe off the inside of the glass jar and remove any paint or dust that may be present.

Alcohol can remove stains and other residues from surfaces by simply wiping them off.

 Polyurethane should be poured.

 I recommend against cutting the spray can. If you are spraying polyurethane and it comes in a can for you to use, you can use it.

Since spray cans are already built to contain a thin layer of polyurethane, there is no need to reduce their thickness further.

Before spraying any polyurethane that does not come in a can with a thinning agent already included, it is recommended to dilute the material.

Therefore, crack open the polyurethane can and transfer an adequate amount of the substance into the glass jar.

 Mineral Spirit or paint thinner can be added to the mixture.

 Then pour mineral spirit or paint thinner into the previously empty glass jar. Maintain the ratio of 1:4 while adding mineral spirits or paint thinner to the glass jar. This means that you should add four polyurethane parts for every part of the mineral spirit.

Use a measuring cup to determine the appropriate proportion of polyurethane to mineral spirit. For example, the mineral spirit should be added to one gallon of polyurethane by pouring one-half cup in.

To get the best results when spraying polyurethane, make the layer of polyurethane as thin as possible.

Because of this, it is increasing the amount of paint thinner or mineral spirit that is added to the polyurethane can be acceptable depending on the kind of application that is being used.

 Mix the Ingredients Well.

 Take the stick that has been thoroughly cleaned, and stir the mixture of polyurethane and mineral spirit for approximately ten minutes.

 When you are stirring, keep even pressure on the stick and stir in a figure 8 motion. This will ensure that the ingredients are thoroughly combined. If you stir the polyurethane mixture too quickly, you can end up with bubbles.

Even after applying coatings, if the air bubbles are unable cannot cause them to be encased within the material, this might be a significant challenge.

After you have finished swirling the mineral spirit and polyurethane combination, you will not observe any air bubbles in the mixture. This is because, at that very moment, the process of thinking polyurethane had already started.

 Experiment with polyurethane.

 After preparing the thinned polyurethane, test it with a spray gun by applying it to a piece of cardboard or wood. After you have completed the application test, you will be able to see the true colors once the polyurethane has dried.

 Congratulations, you have effectively thinned the oil-based polyurethane if the resulting polyurethane layer has no flaws, such as bubbles or differences in color. If this is the case, then the oil-based polyurethane.

If you think the polyurethane is too watery, add a little more polyurethane to the mixture, stir it, and then perform the test once more.

If the polyurethane still has an uneven texture, add a bit more mineral spirit to the mixture, stir it, and then repeat the test.

 The spray gun needs to be loaded with polyurethane.

 Load the polyurethane into the spray gun or sprayer as soon as you have finished thinning the polyurethane, and the resulting mixture has reached the appropriate consistency.

At present, polyurethane is thin, so it is possible to attain a finish that is exceptionally smooth and glossy without leaving any blotches on the surface.

Because it produces better outcomes than its regular counterpart, working with thinned polyurethane is much simpler than working with the ordinary.

In this manner, you should dilute oil-based polyurethane so it can be sprayed.

How Can I Dilute Water-Based Polyurethane So That It Can Be Sprayed?

Water or alcohol that has been denatured can be used to thin water-based polyurethane. The amount of water that is needed for a polyurethane product depends on the type of application as well as the brand.

To obtain a better understanding of water-based polyurethane for spraying, let’s go through each of the procedures that were above in greater depth.

 

Jar made with clean glass.

 When cleaning the jar, follow the same steps when we discussed oil-based polyurethane for spraying.

Because this is where the reaction between the water-based polyurethane and the water occurs, the cleaning glass jar is essential because the reaction must take place in an environment that is clean and free from any interference.

Warm soapy water is used to clean a glass jar, removing dust and any paint that may be present.

 Polyurethane should be poured.

 It is advisable to dilute water-based polyurethane before spraying it, especially if the product does not come in a spray can. Therefore, crack open the polyurethane can and transfer an adequate amount of the substance into the glass jar.

Be sure to grab the glass jar that has adequate capacity for both the polyurethane and the water you need.

 You can add water or alcohol that has been denatured.

 A thin water-based polyurethane can be created by adding water in ever more significant amounts until the appropriate consistency is reached. Add water or denatured alcohol at a volumetric ratio of 2% to 3% of the total volume.

As an illustration, include 0.4 fluid ounces of water into a volume of polyurethane that is 20 fluid ounces.

 Most of the time, the amount of water that should be added to the polyurethane has been specified on the packaging.

To get the best results when spraying polyurethane, make the layer of polyurethane as thin as possible.

Therefore, you should never instantly add 90 percent polyurethane to 10 percent water since this can cause the polyurethane to become overly watery.

The most effective technique for reducing the thickness of polyurethane is gradually incorporating more water into the mixture while simultaneously raising the total amount to the point where it reaches the ideal volume.

 

Mix the Ingredients Well.

 Now, take the clean stick, and stir the mixture of polyurethane and water very gently for around ten minutes.

When stirring, you should only move the polyurethane mixture slowly, as you can end up with bubbles.

Therefore, when stirring, be careful not to shake the mixture too vigorously for too long.

 Experiment with polyurethane.

 After preparing thinned polyurethane, test it by putting a tiny amount of the substance into the spray gun and applying it to a piece of cardboard or wood.

After you have completed the application test, you will be able to see the true colors once the polyurethane has dried.

 If the water based polyurethane layer that results from your efforts has a uniform spray that does not contain any defects, bubbles, or color fluctuations, this indicates that you have successfully thinned the layer.

If you think the polyurethane is too watery, add a little more polyurethane to the mixture, stir it, and then perform the test once more.

If the polyurethane is still too rough, add a little bit more water or denatured alcohol to the mixture, stir it, and then perform the test again.

The spray gun needs to be loaded with polyurethane.

After thinning water based polyurethane and the resulting mixture is uniform and has reached the desired consistency, load the mixture into the spray gun or sprayer and apply it.

You can add as much water as you want, up to a maximum of ten percent, to get an extremely smooth surface by gradually increasing the volume of the water by two to three percent.

To spray polyurethane or water based polyurethane more effectively while avoiding the majority of common pitfalls associated with the material, you should thin it in the manner described above.

FAQ on How To Thin Polyurethane