How to thin Shellac – What you need to know.

Shellac, a wood finish made from lac bug resin, has a short shelf life compared to chemical finishes. It typically lasts 6 to 9 months and thickens quickly. Sunlight and open containers can speed up this process. To extend the life of your shellac and make it easier to apply, it is critical to learn how to thin Shellac.

 

Shellac remains a fan favourite finish for the  benefits it provides in refinishing furniture. however, it can be an expensive product. So how can you extend the shelf life of thickened shellac and save money?

Table of Contents

Why Thin Shellac?

Upon opening a fresh can of Shellac, its thin consistency allows for easy application on wood, drying quickly. As time passes and alcohol evaporates, Shellac thickens. This causes brush strokes to be more visible and increasing the drying time. To maintain a smooth finish, thin the Shellac, so you can apply multiple thin coats.

 

One reason to thin Shellac is if store-bought Shellac is too thick from the onset. For example, Zinsser Shellac is typically a 3-pound cut. Some prefer a thinner 2-pound cut or less, which is about 25 grams of shellac flakes to 100 grams of denatured alcohol. Find the full shellac recipe for this easy process.

shellac being brushed on a wood veneer inlay table

Benefits of Thinning Shellac Finish

When you opt to thin your Shellac, it will once again flow and spread more easily across the wood surface, allowing for a smooth, even application. The thin Shellac can easily penetrate deeper into the wood’s pores, increasing the finish’s protection level. Furthermore, shellac’s self-levelling abilities are higher when the product is at a thinner consistency. 

 

A key benefit of Shellac is its quick drying time. This permits a faster turnaround time for refinishing furniture. The drying is caused by the alcohol solvent in the product. When the denatured alcohol solvent evaporates from the product, causing the product to thicken, the drying time required increases. Thinning the shellac will cause the drying time to decrease.

 

Finally, thinning your Shellac before spraying will benefit you when applying it with a sprayer. With thinning, you will achieve an even spray and reduce the risk of the nozel getting clogged. 

Applying Shellac with Brush

What Type of Alcohol Solvent should you use?

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

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.

Applying Shellac with a brush

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.

Shellac flakes melting in ethanol

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 your own Shellac yet, here’s an easy recipe to get started.

 

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.

How to make your own shellac - tools required

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

There are a few common mistakes people make when thinning Shellac that can lead to a poor finish. Firstly, thinning the Shellac too much. This can make the Shellac too runny, causing it to pool and lead to an uneven finish on your project. It’s essential to find the right balance – thin enough to brush correctly but not so thin that it pools and drips everywhere.

 

Another mistake is not allowing proper drying time between coats. Shellac dries quickly, but sufficient drying is essential for proper adhesion between coats. Applying Shellac too soon, before the previous coat has hardened, can lead to dragging, wrinkling, and uneven sheen. While I aim for my shellac to dry within 15 minutes, I only recoat around an hour later.

 

Over-brushing is a common shellac mistake. Each stroke of the brush should be a single, smooth pass. Overworking the Shellac causes brush marks and bubbles that detract from the finish. Allow the Shellac to self-level after gently brushing it on without repeatedly going over the same spot.

 

Finally, don’t bother thinning a product well past it’s shelf life.  It’s not worth putting a sub-par product on your project to save a few dollars.  If your product is store-bought, it will have a best before date and for home-made it’s around 6 months.  After this period of time, the shellac tends to thicken beyond what is salvagable. 

 

Proper thinning technique, adequate drying time, and a light brush touch are vital to avoiding common Shellac thinning mistakes and achieving a smooth, professional finish

Brush with shellac for application

Final Thoughts

Thinning Shellac properly provides several benefits for wood finishing projects. Thinner Shellac has better flow and levelling over the wood surface, allowing for a smooth, even coat. Unlike thick coats, multiple thin coats create a glass-smooth finish. Thinned Shellac also dries faster, making the finishing process quicker.

 

Now that you’ve learned how to thin shellac, avoid discarding it too soon. Test consistency when thinning and make adjustments if necessary. Following these steps will result in a high-quality, long-lasting shellac finish for your woodworking and furniture restoration endeavors.

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Hey, I'm Sarah, the owner of Bold Wallflowers.

I'm on a self-taught journey through furniture refinishing and restoration, loving every experiment in my workshop.

Join me as I share my discoveries and gained knowledge with our vibrant community of fellow refinishers!

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