How to Thin Shellac: What to Use and How Much to Add

Shellac doesn’t stay the same forever. As alcohol slowly evaporates, the mixture gets thicker and can start dragging under the brush. Other times the shellac was simply mixed heavier than you want for the job.

The way to thin shellac is by adding alcohol, usually denatured alcohol or ethanol, until the finish flows properly again. A small adjustment can make shellac much easier to brush and helps it level into smoother coats.

I thin shellac regularly depending on how I plan to use it. Sometimes the mix just needs loosening so it spreads better. Other times I want a lighter cut so the shellac works as a sealer instead of a full finish. Once you understand what to add and how much to adjust, it becomes a simple part of working with shellac.

Quick Answer: How to Thin Shellac

Shellac is thinned by adding alcohol, usually denatured alcohol, to reduce the mixture’s thickness. Start by adding a small amount, mix thoroughly, and test the flow before adding more. Many refinishers begin by adding about 10% more alcohol and adjust gradually until the shellac brushes smoothly.

Simple thinning method

Add a small amount of alcohol to the shellac.
Mix the solution thoroughly.
Test the flow with a brush.
Add more alcohol in small amounts until the shellac spreads smoothly.

Question	Quick Answer

What do you thin shellac with?

Shellac is thinned with alcohol, most commonly denatured alcohol.

Why would you thin shellac?

Shellac often thickens as alcohol evaporates, or it may be mixed heavier than needed for the job.

How much alcohol should you add?

Add small amounts at a time and test the flow. Many refinishers start by adding about 10% more alcohol and adjust from there.

Can old shellac always be fixed by thinning?

No. Shellac that has passed its shelf life should usually be replaced rather than thinned.

Thinning shellac is less about following an exact recipe and more about adjusting the consistency so it brushes smoothly and builds thin coats. The sections below walk through how this works in practice, including the difference between thinning store-bought shellac and batches mixed from flakes.

Why Thin Shellac?

Fresh shellac usually brushes on easily because the alcohol in the mixture keeps it thin and quick drying. Over time, though, some of that alcohol evaporates and the shellac gradually thickens.

When that happens, the finish can start dragging under the brush and leaving more visible strokes. Thinning the shellac brings the mixture back to a consistency that spreads more easily and allows you to build up thin, even coats.

Another reason people thin shellac is preference. Some store-bought products are mixed heavier than many refinishers like to use. For example, Zinsser shellac is typically a 3-pound cut, while many people prefer working closer to a 2-pound cut.

If you want to slow that thickening down in the first place, proper storage helps. I explain that in how to store shellac properly.

shellac being brushed on a wood veneer inlay table

Benefits of Thinning Shellac Finish

When shellac is thinned to the right consistency, it becomes much easier to work with. The finish flows more smoothly across the wood surface and spreads into thinner, more even coats.

A lighter mix also improves shellac’s natural self-levelling behaviour. Instead of sitting heavily on the surface, the finish settles more evenly as it dries, which helps reduce visible brush strokes. It also gives you more control when you are applying shellac with a brush.

Thinning can also help maintain shellac’s quick drying time. As the mixture becomes thicker, drying between coats can take longer. Adjusting the consistency helps keep the finish behaving the way shellac normally should.

Finally, thinning shellac is often necessary if you plan to spray it. A heavy mix can clog a spray gun, while a slightly thinner one sprays much more evenly.

What to Thin Shellac With

Woodworkers and restorers who make their own shellac have preferences for different types of alcohol. Some prefer denatured alcohol like ethanol or isopropanol, while others prefer pure alcohol with minimal water content. The choice is up to the individual.

Those who prefer pure alcohol believe it produces higher quality shellac because denatured alcohol can interfere with the finish. I am personally in the denatured alcohol camp. I can easily buy denatured alcohol like ethanol in the Netherlands in bulk and have it delivered to my home, which is convenient. I’ve never had any issues with the quality of the shellac I make.

Denatured Alcohol for the purpose of making Shellac for wood working

How you thin shellac depends slightly on whether you are working with store-bought shellac or a batch mixed from flakes.

Thinning Store-Bought Shellac

Store-bought Shellac; such as Zinsser or your other favourite brand, may have small print advising against thinning it. You can disregard this. Even though it may have a longer shelf life than homemade Shellac, it will eventually thicken. This happens naturally as the product is exposed to sunlight or as the alcohol evaporates. The way to thin your shellac is by simply adding your preferred solvent.

Tips for Thinning Store-bought Shellac

Start by transferring some Shellac to a different container. This will allow you to adjust the thickness if you add too much shellac solvent such as ethanol. Store-bought Shellac cannot be thickened by adding more shellac flakes like homemade Shellac can.

What is the ideal ratio to strive for? It varies for each person. Take into account your preference for Shellac thickness. Begin by combining Shellac with a solvent like denatured or ethanol alcohol until you achieve a smooth consistency for application on wood.

If you’re unsure if your Shellac is the right consistency, check how long it takes to dry. I usually thin mine to dry in 15 minutes. A mixture this thin also minimizes drips and brush marks. I rather build up multiple thin layers of shellac, then struggle with 2 or 3 thick layers.

Thinning Homemade Shellac

I love creating my own Shellac because it’s easy and I make small batches as needed to prevent it from sitting around and thickening. If you haven’t tried making shellac from flakes yet, you can follow the simple shellac recipe I use in my workshop.

I have little experience with store-bought Shellac due to its high cost in the Netherlands. Therefore, I learned to make my own because a nearby windmill sells top-notch, dewaxed shellac flakes in various colors.

From what I have seen, homemade shellac quality is based on the quality of the shellac flakes and denatured alcohol that you use. I personally use Shellac Flakes from De Kat Windmill, and I purchase (in bulk) 99.8% ethanol alcohol to use as my solvent. If you use good quality ingredients, you will get a quality product. Furthermore, buying the ingredients separately often means you save a pretty penny in costs as well.

Process of thinning homemade Shellac

The process is easy. Just add more solvent to your existing Shellac mixture and mix. It’s really simple. Remember the proportions of flakes and alcohol you used, and add approximately 10% more of the original alcohol.

So, say that your Shellac was mixed with 100 grams of ethanol alcohol; consider adding 10 grams more and mixing. Test out how smoothly the Shellac brushes now. If you are unsatisfied, add an additional 10 grams or 10% more alcohol. Adding small amounts at a time minimises the risk of over-thinning.

Veneer on a cabinet door front with shellac finish

Common Mistakes When Thinning Shellac

A few common mistakes can quickly ruin a shellac finish if you’re not careful.

The first is thinning the shellac too much. If the mix becomes too runny, it can pool on the surface and create an uneven finish. The goal is simply to loosen the consistency so it brushes smoothly without dripping.

Another issue is recoating too quickly. Shellac dries fast, but the previous coat still needs time to harden properly. I usually let mine dry around 15 minutes before touching it, but I wait closer to an hour before applying the next coat.

Over-brushing is another common problem. Shellac levels well on its own, so once it’s on the surface, leave it alone rather than working the same spot repeatedly.

Finally, don’t try to rescue shellac that’s well past its shelf life. Store-bought products have a best-before date, and homemade batches usually last around 6 months.

If the finish still drags, wrinkles, or dries unevenly, I cover more of those issues in troubleshooting common shellac finish problems.

Brush being loaded with shellac for application

Getting the Right Shellac Consistency

Thinning shellac is really just about adjusting the mix so it flows easily and builds thin, even coats without dragging under the brush. Once you understand how small changes in alcohol affect the consistency, it becomes a simple part of working with shellac.

If you want to keep learning and start using shellac with more confidence, the Shellac Starter Kit includes a decision guide, mixing recipe, and a cost comparison worksheet to help you decide when shellac makes sense and whether mixing your own is worth it for your projects.

Explore the Full Shellac Guide Series

If you’re exploring shellac for furniture refinishing, these guides walk you through the key decisions, techniques, and common questions refinishers encounter.

How to Thin Shellac (What to Use and How Much to Add)