Making a ceramic vase waterproof requires careful work during the vase's creation, but even if the vase looks perfect, a minor flaw can lead to pinpoint holes or unseen cracks that leave the vase leaky. The only way to deal with these minor flaws is by sealing the vase. Several layers of sealant applied to the vase can gain the waterproofing missed during the preparation process. The sealant covers the outside of the vase completely, closing off the tiny holes or cracks in the surface so that the vase will hold liquids without any signs of leakage, adding a level of use to its beauty.
Place the vase onto a level work surface.
Clean the vase with a ceramic cleaner and a soft cloth to remove any dirt from the surface that could interfere with the sealing process.
Place a small pool of acrylic floor sealant onto a piece of cloth. Spread the sealant over the outer surface of the vase with the cloth, taking care to cover the entire vase with the material. Allow the sealant to dry on the vase overnight.
Apply a second coat of sealant to the outside of the vase to augment the first, ensuring that no portion of the vase goes unsealed. Allow an additional 48 hours of drying time before placing any liquid into the vase.
Fill the vase with water and examine the surface for signs of leakage. Allow the water to sit inside the vase for 24 hours, checking occasionally for signs of leaking. If leaks occur, empty the vase, dry it off and apply two further layers of sealant following the same process used for the first two. Repeat the test to make certain the vase is completely sealed, then use the vase as normal.
If the vase still leaks after four layers, then there is a flaw that's too great to be fixed with sealing and the vase cannot be used to hold liquids.