# How to Prevent S-Cracks in Wheel-Thrown Pottery

Source: https://potterynest.com/blog/s-cracks-in-bottom-of-pots
Published: 2026-09-13
Publisher: Pottery Nest

S-cracks are curved or S-shaped cracks that appear in the bottom of wheel-thrown pots, often only discovered after drying or firing. They are one of the most common problems for new potters, and they can ruin an otherwise successful piece. S-cracks come from uneven stress in the base, usually because clay particles in the bottom were not compressed and aligned during throwing. Good throwing habits and even drying prevent most of them.

## Why S-cracks form

When clay is centred and opened on the wheel, the particles in the base are spun into a spiral pattern. If the base is not compressed, those particles remain loosely aligned and shrink unevenly as the pot dries, which creates stress along the spiral and eventually a crack.

Water pooling in the bottom of the pot during throwing softens the base and makes it weaker. Bases that are much thicker than the walls also dry more slowly and shrink differently, increasing stress.

## Compress the base

After opening the clay, compress the floor of the pot with your fingers, a sponge or a rib, moving from the centre outward and back several times. Compression aligns particles and strengthens the base.

Many potters also compress again after pulling the walls, especially on wide bowls and plates. A rib designed for compressing floors helps apply even pressure.

## Remove standing water

Sponge out water that collects in the bottom of the pot while throwing. Soggy clay in the base expands and then shrinks more as it dries.

Use a sponge on a stick for tall or narrow forms. Removing water also makes the base firmer and easier to trim later.

## Keep base thickness even

A base that is very thick in the centre and thin toward the edges dries unevenly. Check base thickness with a needle tool before pulling walls, and aim for an even floor thickness suited to the form.

When trimming, avoid leaving the centre much thicker than the rest of the base, and compress the trimmed foot area lightly with a rib if it looks rough.

## Dry slowly and evenly

Pots dry fastest at the rim and walls, while the base stays wet longer, especially if pots sit on non-porous surfaces. Uneven drying adds stress and can open cracks.

Dry pots slowly under loose plastic, and flip them upside down once the rim is firm enough so the base dries at a similar rate. Placing pots on ware boards or drying racks lets air reach the bottom.

## Check your clay

Some clay bodies are more prone to S-cracks, particularly smooth clays with fine particles and porcelain. Clay with grog or sand can be more forgiving for beginners.

Wedge clay thoroughly to remove air and even out moisture. Recycled clay that has not been fully mixed can also create weak spots that crack.

## Related buying guides

- https://potterynest.com/best/best-pottery-ribs
- https://potterynest.com/best/best-ware-boards
- https://potterynest.com/best/best-clay-for-beginners