ᐅ Cracks are forming at the joints in the Kallax unit – what can be done?

Hello everyone,

While assembling my new Kallax shelf, I noticed small gaps and unevenness at the joints between the shelves and side panels. These are not only visually distracting but also cause instability when placing items, as they can wobble or tip slightly. All the shelf parts were properly glued and screwed together, yet the issue remains.

I suspect this might be due to material expansion or uneven load distribution, but I’m not entirely sure. Does anyone have experience with this problem and practical advice on how to smooth out or at least visually hide the joints? I’m also interested in hearing about sanding or filler work if that makes sense.

Thanks in advance for your help!

Hello vinpi,

Joints between Kallax units often show unevenness due to slight manufacturing tolerances of the particle boards as well as material stresses caused by assembly and environmental conditions (humidity, temperature).

The first step is to check the flatness using a spirit level or a straightedge. If the irregularities are minor (under 1–2 mm (0.04–0.08 inches)), carefully sanding the edges with sandpaper (grit 120 to 240) is recommended. Use a sanding block to keep the surface even and straight.

Alternatively, wood filler can be used to fill larger gaps; after drying, sand the area and, if needed, paint or stain to achieve a uniform appearance.

It is important that the substructure (e.g., wall mounting or base support) is absolutely stable and level to avoid tension and deformation.

In short: measure, sand, fill, and then finish — these are the proven steps to follow.

usbla schrieb:
Cracks at the Kallax joints often result from minimal manufacturing tolerances of the chipboard as well as stresses in the material caused by assembly and environmental conditions (humidity, temperature).

That sums it up very well. To add:

I recommend analyzing the exact cause of the cracks before any repairs. Are they due to manufacturing tolerances, or are external factors (e.g., high humidity or temperature fluctuations) causing the wood-based materials to expand and contract?

A sensible approach would be:
1. Check all joints again for a secure fit, especially the tongue-and-groove connections.
2. Measure the moisture content of the material using a thickness gauge.
3. If moisture absorption is the cause, try letting the furniture rest in a dry place with constant temperature before performing any repairs.

If the cracks are caused by slight unevenness, then careful sanding, as usbla suggests, is recommended.

Regarding fillers: I prefer using a flexible wood filler that does not crack even with slight movements. Especially for Kallax, which is often placed in living rooms and exposed to fluctuating conditions, I would avoid very hard fillers.

One more tip: Small unevenness can sometimes be stabilized using adhesive furniture braces or special connectors on the backside. These reduce movement at the joints and can help minimize the formation of cracks.

Finally: What looks good aesthetically is not always ideal functionally. When in doubt, it is better to accept small visible cracks than to risk unstable furniture.

TEBILO schrieb:
If the cause is moisture absorption, try to let the piece of furniture rest in a dry place at a constant temperature before making any repairs.

Exactly, that’s how I did it. Afterwards, I worked on the edges with fine sandpaper, everything turned out perfect.

vinpi schrieb:
Does anyone know this issue and have practical tips on how to smooth the transitions or at least mask them visually?

I can really understand how frustrating this is. I experienced something similar, and what helped me most—besides sanding and filling—was patience. It’s also worth considering how the shelf will be used and how much pressure the edges need to withstand. Sometimes attaching small spacers or transparent rubber pads underneath can help reduce wobbling. It might not be a perfect visual finish, but the feeling of stability makes a big difference.

Are there specific items on your shelf that wobble more than others? That information could help find a better solution.