How to Prevent Underglaze From Sticking to the Kiln Shelf

It can be frustrating to spend hours carefully painting your underglaze design onto a piece of pottery, only to have it stick to the kiln shelf during firing. Not only does this ruin your hard work, but it can also damage the kiln shelf and cause future pieces to stick as well.

Fortunately, there are several steps you can take to prevent underglaze from sticking to the kiln shelf.  You can also use these methods on how to prevent underglaze from sticking to the kiln shelf to prevent other types of glaze from sticking as well.

What Causes Underglaze to Stick to the Kiln Shelf?

Before we dive into prevention methods, it’s important to understand why underglaze sticks to the kiln shelf in the first place. Underglaze is a type of glaze that is applied onto pottery before firing. It contains high levels of flux, which allows it to adhere to the clay and create vibrant colors. However, this high flux content can also cause the underglaze to melt and stick to the kiln shelf if certain conditions are not met during firing.

One common reason for underglaze sticking is using a low-fire clay body with a high-fire underglaze. The temperature at which the clay and underglaze mature may not match up, causing them to fuse together and stick to the kiln shelf.

Another reason is not applying enough kiln wash or refractory coating onto the kiln shelf before firing. The underglaze can then adhere directly to the bare shelf, creating a strong bond that is difficult to remove.

Why is it Important to Prevent Underglaze From Sticking?

Preventing underglaze from sticking to the kiln shelf not only saves your hard work and prevents damage to the kiln, but it also ensures that future pieces will not stick as well. If underglaze sticks to the kiln shelf and you continue firing, it can create a buildup of glaze on the shelf, making it difficult to remove and potentially damaging future pieces. Additionally, removing stuck underglaze can be a time-consuming and tedious process, so prevention is key.

Needed Tools and Materials

Kiln Wash or Refractory Coating

The most important tool for preventing underglaze from sticking to the kiln shelf is a good layer of kiln wash or refractory coating. Kiln wash is a mixture of alumina hydrate, kaolin, and flint that creates a barrier between the underglaze and the kiln shelf. Refractory coating is a liquid version of kiln wash that can be sprayed onto the shelf for a more even and consistent application.

Soft Bristled Brush

To apply kiln wash or refractory coating, you will need a soft bristled brush. This type of brush is gentle on the surface of the kiln shelf and helps to evenly distribute the coating.

Kiln Shelf

Of course, you will also need a kiln shelf to prevent underglaze from sticking. Make sure to clean and smooth the surface of the shelf before applying any coating.

Gloves

Always wear gloves when handling kiln wash or refractory coating to protect your hands from any potential irritation or chemicals.

11 Step-by-step Guidelines on How to Prevent Underglaze From Sticking to the Kiln Shelf

Step 1: Prep the Kiln Shelf

Before applying any coating, make sure to clean and smooth the surface of your kiln shelf. This will help create an even surface for the coating to adhere to. You can use sandpaper to smooth out any rough spots or leftover glaze from previous firings.

But be sure to wipe away any dust or debris with a clean cloth before moving on to the next step. The smoother the surface, the better the coating will adhere. If your kiln shelf is new, you can also preheat it in the kiln to remove any moisture that could cause the coating to flake off.

Step 2: Mix Kiln Wash or Refractory Coating

If you are using kiln wash, mix it according to the manufacturer’s instructions. If you are using refractory coating, shake the container well before use. If you are using a spray bottle, make sure it has an even misting function to create a smooth and consistent layer.

But, if you are using a brush-on coating, make sure to mix the solution well before application. You want a smooth and creamy consistency, similar to pancake batter. If the coating is too thick, add water a few drops at a time until it reaches the desired consistency.

Step 3: Apply First Coat

Using your soft bristled brush, apply a thin and even layer of kiln was or refractory coating onto the kiln shelf. Make sure to get into all the corners and edges of the shelf as well. Do not apply too thick of a layer, as this can cause cracking or flaking during firing. You can also use a spray bottle for an even coating.

It’s important to apply kiln wash or refractory coating on a cool shelf to prevent it from drying too quickly. But, make sure the shelf is dry before moving on to the next step. You can also use a fan to help speed up the drying process.

Step 4: Let Dry

Allow the first coat to dry completely before applying a second coat. This usually takes around 30 minutes to an hour depending on the temperature and humidity in your workspace. The coating should appear matte and dry to the touch before moving on.

It’s important to let each coat dry before applying the next. You can also use a fan to help speed up the drying process. But, make sure not to direct the fan directly at the shelf, as this can cause uneven drying. It’s important to apply at least three coats in total, but you can add more if desired.

Step 5: Sand Down Any Bumps or Rough Spots

After the first coat has dried, gently sand down any bumps or rough spots with a fine-grit sandpaper. This will help create a smooth surface for the second coat to adhere to. Be careful not to sand off too much of the first coat.

The goal is to create an even and smooth surface, not to remove the coating entirely. If using a spray-on coating, you may not need to sand between coats. The even misting application usually creates a smooth surface without any bumps. It’s always a good idea to test the surface with your fingers before moving on to the next step.

Step 6: Apply Second Coat

Once you have sanded down any rough spots, apply a second coat of kiln wash or refractory coating. This will create an extra layer of protection and ensure that the underglaze does not stick to the shelf. Make sure to apply the second coat in the same manner as the first, with a thin and even layer.

Let dry completely before moving on to the next step. You can also repeat this step and apply a third coat if desired. The more layers of coating, the better protected your kiln shelf will be. The average is 2-3 coats.

Step 7: Repeat as Needed

For added protection, you can repeat steps 5 and 6 for a third or even fourth coat of kiln wash or refractory coating. This will create an even stronger barrier between the underglaze and the kiln shelf. However, make sure to let each coat dry completely before applying another. it’s important not to rush this process.

It can take a few hours, but it’s worth the extra time for a well-protected kiln shelf. But, if you are satisfied with the second coat, you can move on to the next step. It’s always a good idea to test the surface with your fingers before moving on.

Step 8: Sand Final Coat (Optional)

If you have applied multiple coat of kiln wash or refractory coating, you may want to consider sanding down the final coat for an extra smooth surface. This will help prevent any bumps or ridges from forming during firing.

However, if you are using a spray-on coating, this step is not necessary. You can also use a damp cloth to gently smooth out any bumps or ridges if needed. You want the surface to be as smooth as possible for the underglaze application. But, make sure to let the final coat dry completely before moving on to the next step.

Step 9: Let Dry Completely

After all coats have been applied and sanded (if desired), let the final coat dry completely. This usually takes around an hour, but it’s important not to rush this step. The coating should be completely dry before firing to prevent cracking or flaking during the firing process.

But, if you are in a hurry, you can use a fan to help speed up the drying process. The coating should be completely dry before moving on to the next step. If you are using a spray-on coating, it may take longer to dry than a brush-on coating.

Step 10: Fire Your Pieces

Once the coating is dry, you are ready to fire your pieces in the kiln. Make sure to follow your specific glaze and firing instructions for best results. The barrier created by the kiln wash or refractory coating will prevent any underglaze from sticking to the kiln shelf during firing.

If you experience any sticking or issues, it may be a sign that the coating needs to be reapplied. But, with proper application and maintenance, you should have no problems with underglaze sticking to your kiln shelf.

Step 11: Clean and Reapply After Firing

After your pieces have been fired, make sure to clean the kiln shelf and remove any leftover glaze or underglaze. You can use a scraper or sandpaper to gently remove any residue. Make sure not to damage the coating while cleaning. Once the shelf is clean, you can reapply a thin layer of kiln wash or refractory coating before your next firing.

This will help maintain the protective barrier and ensure that your pieces don’t stick to the shelf in future firings. And remember, always clean and resurface your kiln shelf before each firing for best results. 

Overall on how to prevent underglaze from sticking to the kiln shelf, properly applying and maintaining a kiln wash or refractory coating is essential for a smooth and successful firing process. With these steps, you can ensure that your pieces will come out of the kiln without an unwanted layer of kiln shelf attached to them. Happy firing! 

Things to Remember

• Use a Soft Bristled Brush or Spray Bottle for Even Application 
• Allow Each Coat to Dry Completely Before Applying the Next 
• Sand Down Any Bumps or Rough Spots Between Coats 
• Consider Adding Multiple Coats for Added Protection 
• Let the Final Coat Dry Completely Before Firing 
• Clean and Reapply After Every Firing for Best Results.

In addition, it’s important to use a kiln wash or refractory coating specifically designed for ceramic firing. Other products may not withstand the high temperatures of a kiln and could potentially harm your pieces. And always follow the instructions provided by the manufacturer for best results.

With proper application and maintenance, you can prevent underglaze from sticking to your kiln shelf and achieve beautiful and successful firings every time. 

Needed for Maintenance

• Kiln Wash or Refractory Coating 
• Soft Bristled Brush or Spray Bottle 
• Fine-grit Sandpaper 
• Fan (Optional) 
• Damp Cloth (Optional)
• Scraper or Sandpaper (for Cleaning After Firing)  .

By taking the time to properly prepare your kiln shelf and maintain it, you can prevent the frustration and disappointment of underglaze sticking to your pieces. Follow these steps and always stay on top of maintenance for a smooth firing process.

Do You Need to Get Rid of Stubborn Underglaze Stains on Your Kiln Shelf?

If you have already experienced underglaze sticking to your kiln shelf, don’t worry. There are a few things you can do to remove the stubborn stains and get your kiln shelf back in working order. Some methods include using strong chemicals or sanding down the surface, but these options can be risky and may damage your kiln shelf.

For best results, it’s recommended to seek professional help or replace the kiln shelf altogether. Prevention is always the best method for avoiding this issue. So, make sure to follow these steps and properly maintain your kiln shelf to prevent underglaze from sticking in the first place.  .

With a little bit of patience and proper maintenance, you can keep your kiln shelf clean and your firings successful.

Frequently Asked Questions

Q: Do I Need to Add Multiple Coats of Kiln Wash or Refractory Coating?

A: It is recommended to apply at least two coats, but you can add more for added protection. Just make sure to let each coat dry completely before applying the next one. You can also sand down any bumps or rough spots between coats. It’s better to have too many coats than not enough for a well-protected kiln shelf.

Q: Can I Reuse the Same Kiln Wash or Refractory Coating?

A: Yes, you can reuse the same coating multiple times before needing to reapply. Just make sure to clean and resurface your kiln shelf between each firing for best results.

Q: Can I Use a Different Product Instead of Kiln Wash or Refractory Coating?

A: No, it’s important to use a product specifically designed for ceramic firing. Other products may not withstand the high temperatures of a kiln and could potentially harm your pieces. Always follow the instructions provided by the manufacturer for best results.

Q: How Often Do I Need to Clean and Reapply the Coating?

A: It is recommended to clean and reapply the coating before each firing for best results. This will ensure that your kiln shelf is properly protected and your pieces won’t stick during firing.  However, if you notice any issues with sticking or residue buildup, it may be necessary to clean and reapply more frequently.

Q: Can I Use a Kiln Wash or Refractory Coating on Any Type of Kiln Shelf?

A: Yes, you can use these products on any type of kiln shelf as long as it is designed for ceramic firing. Make sure to follow the instructions provided by the manufacturer for best results. Otherwise, you may risk damaging your kiln shelf or pieces. 

Conclusion

Properly applying and maintaining a kiln wash or refractory coating is crucial for preventing underglaze from sticking to your kiln shelf. By following these steps and staying on top of maintenance, you can ensure successful firings every time.

Remember to use the right tools and products, allow adequate drying time, and clean and reapply after each firing for best results. With these tips on how to prevent underglaze from sticking to the kiln shelf, you can achieve beautifully glazed pieces without the frustration of dealing with a stuck kiln shelf.  Happy firing!