How To Thin Water Based Polyurethane? 3 Methods To Do It

You might have just finished your grouting. However, you would like to coat the grout with water based polyurethane. But you think it’s quite dense. 

So, your concern is, how to thin water based polyurethane?

First of all, you can try thinning with Floetrol. Besides that, you would also like to try on paint thinner. However, if you’re using paint thinner, you need to be careful about its properties. Lastly, you can follow one of the simplest methods. That method is just adding water to your polyurethane.

This information is surely not enough for you. So, make sure to read along for the main part!

Sounds good? Let’s just get into it then!

WaterAdding water to water-based polyurethane to reduce its viscosity and make it thinner.Easy and readily available. Does not affect the drying time.Can dilute the polyurethane, reducing its durability and protection. Excessive water may cause the polyurethane to lose its effectiveness. May require multiple coats for desired finish.
Mineral SpiritsAdding mineral spirits (a type of solvent) to water-based polyurethane to thin it.Allows for better control of viscosity. Does not affect the drying time.Requires additional purchase of mineral spirits. May have stronger odor and more volatile fumes compared to water. May still require multiple coats for desired finish.
Floetrol or PenetrolAdding a paint conditioner such as Floetrol or Penetrol to water-based polyurethane to thin it.Specifically designed for improving flow and leveling of water-based coatings. Can help achieve smoother finishes.Requires additional purchase of paint conditioner. May affect the drying time and may require adjustments to application techniques.
Manufacturer’s ThinnerUsing the specific thinner recommended by the manufacturer of the water-based polyurethane.Ensures compatibility and optimal results. May not affect the drying time or performance of the polyurethane.Requires purchase of manufacturer’s recommended thinner. May be more expensive compared to other methods.

Why Should You Thin Water Based Polyurethane?

Water-based polyurethane should be thinned for a variety of reasons. One of the reasons is to enable it to be used in an HVLP spray gun. For optimal spraying outcomes, most spray guns require thinning. 

See also  How To Seal Creosote Lumber? 3 Easy Steps

Your brush will slide more smoothly this way. Thus, you won’t have a roughly brushed finish. 

Another common reason for thinning water-based polyurethane is making it look natural. That is, it would look quite natural when you apply it to the grout.

How To Thin Water Based Polyurethane

3 Simple Methods To Thin Water Based Polyurethane

Well, you’ve already got to know a brief about the methods. However, you need to go through the description of the method to implement them properly.

So, without any further due, we’re going to the main part, discussed below-

Method 1: Thinning Water Based Polyurethane with Floetrol

A lot of people ask “Can I thin water based polyurethane with Floetrol?” 

Yes, you are capable of doing the task. To do so, first, you need to mix Floetrol with your water based polyurethane. Make sure to add a water maximum of 10% in amount. Don’t add any more than that. Because adding more than that would completely spoil your polyurethane.

Then stir and mix it properly. It would make the polyurethane have a better flow during the application. 

However, an important point must be added to it! We know that Floetrol can be used to thin water-based polyurethane. Your water-based poly, on the other hand, might turn yellow with time. This happens especially if you add more Floetrol than required. 

Method 2: Using Paint Thinner to Thin Water Based Polyurethane

Now, you may ask how to thin water based polyurethane for spraying?

You can do it using paint thinners! Paint thinners can be created from a wide range of materials. However, they could have a variety of odors and toxicity levels. As a result, be sure the paint thinner you buy is compatible with polyurethane goods.

So, to begin with paint thinner, you need to make up the polyurethane first. At first, a clean stirring stick is required. Then, with the stirring stick, slowly mix the polyurethane in a figure-eight motion. 

Now, coming back to the method again. Make sure to scrape all of the thick material from the can’s bottom. Then whisk the polyurethane until it has a homogenous texture. 

See also  Can You Put Polyurethane Over Polycrylic (What's The Real Fact)

An important point must be added. If you shake the can, air bubbles would form. This would result in a less-than-smooth finish in the end.

Anyway, now, add the paint thinner slowly in several batches. Make sure you don’t add it too much. Polyurethane can be added up to 10% of the time. But adding more than that would most likely spoil your water based polyurethane.

Nevertheless, you can still use it to thin your water based polyurethane with no worries!

Method 3: Adding Water to The Water Based Polyurethane

A lot of people ask how to thin water based polyurethane for wiping?

So, here’s how you can do it using water. This is the simplest method to follow. 

However, this might not be followed by everyone. Because this doesn’t seem to be effectively workable to everyone. Moreover, adding water might also deteriorate the quality according to some people.

Nevertheless, you might still want to know about this method. So, all you need to do is just add water to your water based polyurethane. Do it before you apply the polyurethane. Make sure that you don’t add more than 10% of it. Finally, stir the mixture properly. 

Extra tip: Water can be used to thin any water-based substance, including finishes and paints. When using a brush to apply water-based polyurethane, remember to thin it out. You’ll have more time until it dries if you do it this way.

Method 4: Using Mineral Spirits

Step 1: Prepare the Polyurethane

Pour the desired amount of water-based polyurethane into a clean container.

Step 2: Add Mineral Spirits

Add mineral spirits to the polyurethane gradually. Start with a small amount and mix it thoroughly before adding more. Follow the manufacturer’s recommendations for the appropriate ratio of mineral spirits to polyurethane.

Step 3: Stir Well

Use a stir stick or paint stirrer to mix the mineral spirits and polyurethane thoroughly. Stir in one direction to avoid introducing air bubbles. Continue stirring until the mixture reaches the desired consistency.

See also  What Finish To Use For Wooden Coasters: An Easy Guide

Method 5: Using a Specific Thinning Agent

Step 1: Identify a Suitable Thinning Agent

Certain brands offer specific thinning agents formulated for their water-based polyurethane products. Identify a suitable thinning agent based on the brand and product recommendations.

Step 2: Follow Manufacturer’s Instructions

Follow the manufacturer’s instructions on how to use the specific thinning agent. The instructions may vary depending on the brand and product. Ensure that you measure and mix the thinning agent as directed.

So, these are the techniques for thinned water-based polyurethane.

Precautions and Tips

When thinning water-based polyurethane, consider the following precautions and tips:

  1. Wear protective gear, including gloves, safety goggles, and a mask, to prevent contact with the skin and inhalation of fumes.
  2. Test the thinned polyurethane on a small, inconspicuous surface before applying it to the entire project.
  3. Maintain proper ventilation in the work area to ensure good air circulation.
  4. Follow the manufacturer’s recommendations for thinning ratios and application methods.
  5. Clean brushes and other tools promptly after use to prevent the polyurethane from hardening.

Application of Thinned Polyurethane

Once the water-based polyurethane is thinned to the desired consistency, apply it using a brush, roller, or sprayer according to the manufacturer’s instructions. Follow proper application techniques and allow sufficient drying time between coats.

Cleaning Up

Clean brushes, rollers, and other tools immediately after use with soap and water. Dispose of any excess thinned polyurethane according to local regulations.


Question: How do you make polyurethane thinner?

Answer: You can do it with mineral spirits and varnish. Add 3 or 4 parts of varnish to 1 part of mineral spirits The ratio isn’t important. You can use a rag to apply these finishes if you want. If that’s the case, dilute them with 50 percent mineral spirits.

Question: Can water-based varnish be thinned?

Answer: Yes you can thin the water-based varnish. You can do it with water. This would improve atomization. The thinning is not the same as lacquer, though. A small amount of water makes a considerably bigger effect on lacquer than lacquer thinner. So start with 5% or less and see how things go.

Question: Can you wipe on polyurethane? 

Answer: Polyurethane is one of the most popular, long-lasting, and versatile finishes. It’s simple to apply, provides good protection, and adds a lovely sheen to the wood. Wipe-on or dry-erase markers can be used for the majority of your job. However, it depends on the project. Brush-on polyurethane can also be used for this.

Question: Can you thin varnish with paint thinner?

Answer: Yes, paint thinner can be used to thin varnish, but it’s important to check the manufacturer’s instructions as some varnishes may require a specific type of thinner.

Question: Can you spray water based polyurethane?

Answer: Yes, water-based polyurethane can be sprayed, but make sure to use a sprayer designed for water-based finishes and follow the manufacturer’s guidelines for proper application.

Question: Which on is the best thinner for polyurethane?

Answer: The best thinner for polyurethane depends on the specific product, but generally, water is the recommended and most commonly used option for thinning water-based polyurethane.

Final Words

Now, you know how to thin water based polyurethane! We believe our methods are quite simple and easy to follow. 

We would hope you follow our methods. Make sure to get in touch with us for any queries regarding water based polyurethane.

Leave a Reply

Your email address will not be published. Required fields are marked *