Joining slip is the adhesive that holds handbuilt pottery together. It’s made from the same clay body you’re working with, which means it shrinks at the same rate as your piece during drying and firing. That compatibility is what makes it work — unlike commercial adhesives or water alone, joining slip becomes part of the clay when it dries.
What Makes a Good Joining Slip
The slip should be the consistency of thick cream — spreadable but not runny. Too thin and it doesn’t provide enough bond; too thick and it creates a heavy layer that shrinks differently from the surrounding clay and can cause cracks at the join. Always use slip from the same clay body you’re building with. Different clay bodies shrink at different rates — a mismatched slip will pull the join apart.
Materials
- Bone dry clay scraps or trimmings from the same clay body
- Immersion blender
- Two containers with lids — deli cups or yogurt containers work well
- Ziploc bag
- Rubber mallet
- Water, vinegar, or magic water
Step-by-Step
1. Collect and Dry Your Clay Scraps
Save trimmings, failed pieces, and throwing slip from your wheel sessions — all from the same clay body. Let them dry completely to bone dry. Bone dry clay breaks down into slip much more easily than leather-hard or wet clay. Keep a dedicated container to collect scraps between studio sessions.
- Safety note: Dry clay creates silica dust. Keep scraps in a sealed bag or container while drying and always crush them in a sealed bag — never in open air.
2. Crush the Dry Clay
Place the bone dry scraps inside a sealed Ziploc bag. Use a rubber mallet to crush them into a fine powder. Keep the bag sealed — you don’t want a cloud of silica dust in the air.
3. Add Liquid
Pour your liquid into a clean container first, then slowly add the clay powder. The ratio is roughly equal parts by volume as a starting point — adjust until you reach the right consistency. Liquid options:
- Water: Straightforward, works for most standard joins at matching moisture levels.
- Vinegar: Adds tack and acts as a mild deflocculant. Good for leather-hard to leather-hard joins.
- Magic water: The strongest option. Use for difficult joins, pieces at different dryness stages, or when extra insurance is needed.
4. Let It Soak
Let the clay powder sit in the liquid for at least a few hours — overnight is better. The clay needs time to fully absorb the liquid and soften before blending.
5. Blend Smooth
Use an immersion blender to blend the mixture until smooth with no lumps. Don’t over-blend — a minute or two is enough. Check the consistency and add more liquid or clay powder to dial it in.
6. Store with a Lid
Store in a sealed container. Joining slip keeps indefinitely as long as it doesn’t dry out. If it thickens over time, add a small amount of water and stir. Label the container with the clay body so you don’t mix them up.
How to Use It
Always use joining slip as part of the full slip and score process — score the surfaces first, then apply slip to both sides before pressing together. Slip on unscored surfaces won’t hold.
