How to Seal Clay Pottery

Sealing clay pottery is an essential step to ensure its durability, functionality, and longevity.

Whether you’re creating decorative pieces or functional items like planters or bowls, sealing helps protect the pottery from moisture, staining, and wear over time. This guide will provide you with how to seal clay pottery and preserve its beauty and quality.

Why Seal Clay Pottery?

Sealing clay pottery is crucial for maintaining the integrity and appearance of your creations. Unsealed clay pottery is porous, meaning it can absorb water, oils, or other substances it comes into contact with. Over time, this can lead to cracks, discoloration, or even structural damage.

For functional pieces like plant pots or dinnerware, sealing ensures they are water-resistant, making them more practical for everyday use. Additionally, sealing enhances the finish of the pottery, giving it a polished and professional look. Whether for artistic or practical purposes, properly sealing your pottery preserves its quality and helps it withstand the test of time.

Types of Clay Pottery and Their Sealing Needs

Different types of clay pottery come with unique characteristics that influence their sealing requirements.

1. Earthenware 

  Earthenware is a porous type of pottery fired at lower temperatures, making it especially prone to absorbing liquids and stains. To ensure durability and functionality, earthenware often requires a dependable sealant like a food-safe glaze, particularly if used for serving food or holding water.

2. Stoneware 

  Stoneware is more durable and less porous than earthenware, as it is fired at higher temperatures. While stoneware can sometimes be used without sealing, a glaze finish is often applied to enhance its appearance and to ensure complete water resistance, particularly for functional items like mugs and bowls.

3. Porcelain 

  Known for its translucence and fine texture, porcelain is non-porous after high-temperature firing. However, sealing or glazing porcelain is typically done to enhance its appearance or add unique textures and colors, rather than to improve durability or waterproofing.

4. Terracotta 

  Terracotta is a specific type of earthenware that is highly porous and frequently used for items like plant pots and decorative pieces. Since it easily absorbs water, sealing is often necessary for outdoor use or to prolong its lifespan. A breathable sealant is commonly used for plant pots to allow proper moisture and air exchange.

Understanding these differences ensures that the right sealing method is chosen for each type of pottery, preserving functionality and aesthetics.

10 Methods How to Seal Clay Pottery

1. Using Ceramic Glaze for Functional Sealing

One of the most common and effective ways to seal pottery is through glazing. After the clay has been bisque-fired, a ceramic glaze can be applied with a brush, dip, or spray method. Glazes are essentially a mixture of silica, fluxes, and colorants that melt during the final firing to form a glass-like, impermeable surface.

Not only does glazing seal the pottery, but it also allows for vibrant colors and decorative finishes. Glazing is especially ideal for food-safe items like cups, bowls, and plates. After glaze application, the pottery must be fired again in a kiln at a specific temperature to vitrify the glaze, making it durable and waterproof.

2. Applying Food-Safe Sealers for Air-Dry Clay

Air-dry clay does not undergo kiln firing and remains porous even when fully hardened. To make such pottery water-resistant and suitable for decorative or light functional use, a food-safe, water-based sealant like Mod Podge or a specialized acrylic polymer can be applied. These sealers are typically brushed on in multiple thin layers, allowing each coat to dry completely before applying the next. While this does not make air-dry clay entirely waterproof, it greatly enhances its resistance to moisture and stains. This method is perfect for pots, vases, or sculptural items not intended to hold water for long durations.

3. Using Epoxy Resin for Maximum Water Resistance

For pottery that must be completely sealed and waterproof—such as planters or indoor fountains—epoxy resin offers one of the strongest and most durable solutions. Epoxy is a two-part compound that cures into a hard, plastic-like finish. Once mixed and applied, it can be brushed or poured onto the pottery surface, covering it thoroughly. It is important to apply it in a dust-free environment and allow full curing time, which may range from 24 to 72 hours. Once hardened, epoxy provides a glossy, waterproof seal that is both long-lasting and highly resistant to wear.

4. Rubbing with Wax for Rustic Sealing

An old-fashioned but effective technique, waxing is a natural way to seal porous pottery surfaces. Beeswax or carnauba wax can be melted and applied to bisque or low-fired pottery using a cloth or brush.

Once the wax is absorbed into the clay body and cooled, it forms a water-resistant barrier that enhances the pottery’s earthy texture and tone. This method is ideal for decorative pieces or rustic-style pottery where a natural look is desired. While wax does not make pottery fully waterproof, it adds a modest level of moisture protection and an appealing soft sheen.

5. Boiling in Milk for Primitive Clay Sealing

An ancient method of sealing low-fired or earthenware pottery involves boiling it in milk. The proteins in milk—especially casein—react with the clay’s porous surface and form a natural seal when heated. To use this method, submerge the unfired or low-fired pot in whole milk and slowly bring it to a gentle boil. Simmer for about 30 minutes and then allow it to dry completely. The casein fills the pores and creates a mild sealant that repels water. Though not as durable as synthetic coatings, this traditional method is eco-friendly and adds a soft, natural finish.

6. Sealing with Linseed Oil for Matte Protection

Linseed oil, derived from flax seeds, is another natural sealer suitable for decorative pottery. Especially effective for terracotta or porous surfaces, linseed oil can be applied with a clean cloth, penetrating deep into the clay. Multiple applications may be required, allowing the piece to dry thoroughly between coats. The oil cures slowly and provides a matte, slightly darkened finish. This method does not create a fully waterproof barrier but helps prevent moisture absorption and is ideal for plant pots, outdoor pottery, and rustic vessels that do not require a glossy finish.

7. Spraying Acrylic Sealant for Quick Finishing

Acrylic sealant spray is a convenient and effective way to seal both air-dry and bisque pottery. Available in matte, satin, and gloss finishes, these sealants create a flexible, transparent film that helps protect the surface from moisture, stains, and UV damage.

The pottery should be clean and completely dry before spraying. Apply light, even coats in a well-ventilated area, allowing adequate drying time between layers. This method is perfect for craft projects, decorative items, and small pottery pieces where speed and ease of application are priorities.

8. Using Waterproof Tile Sealer for Outdoor Pieces

When sealing clay pottery intended for outdoor use—such as garden pots, birdbaths, or statues—waterproof tile or stone sealers offer excellent performance. These sealers, designed for masonry and ceramics, penetrate the clay surface and form a breathable, water-repellent barrier. They are usually applied with a brush or sponge and left to cure for several hours. Once dry, they protect against rain, humidity, and freeze-thaw cycles, helping prevent cracking and water damage. This method is especially useful for larger or structurally exposed pottery pieces that must withstand the elements.

9. Sealing from the Inside for Functional Pottery

For functional pieces like pitchers or cups, sealing the interior is especially important. In such cases, a food-safe waterproofing product should be applied only to the inside surface. Ceramic glazes, epoxy resin, or food-grade waterproof coatings can be used to ensure no liquid seeps through the clay body. After sealing the interior, it is essential to test the piece with water to check for leaks or absorbency. A proper interior seal is crucial for ensuring safety and functionality in everyday-use pottery.

10. Combining Sealants for Layered Protection

In some instances, combining multiple sealing techniques yields the best results. For example, pottery can first be treated with linseed oil or a penetrating sealer to strengthen and condition the clay, then finished with a topcoat of acrylic or wax. For air-dry clay sculptures, applying an acrylic base coat followed by a resin finish creates both visual depth and a strong protective barrier.

When layering sealants, it is critical to ensure each layer is compatible with the next and fully dried before the next application. This method is best used on decorative pieces requiring both aesthetics and durability.

Conclusion

Sealing clay pottery is a multifaceted process influenced by the intended use, the type of clay, and the artist’s personal preferences. From traditional milk boiling to modern epoxy application, each method offers distinct advantages and considerations.

Whether your goal is to create a waterproof vessel, a food-safe dish, or a beautiful decorative piece, the key to success lies in selecting the appropriate sealing method and applying it with care. With the guidance of these ten detailed approaches, potters of all levels can confidently enhance the strength, appearance, and longevity of their clay creations. Thanks for reading our blog post on how to seal clay pottery! We hope you found it helpful and informative.