The most common defects in large porcelain slabs are bowing or twist, shade differences between slabs, printing faults, polishing marks, chipped edges and corners, hairline cracks and errors in size or squareness. Book-matched slabs add one more: sets that do not line up.
Many of these also occur on tiles. On slabs they are more visible, because each piece covers a large area and sits next to only a few joints.
Shape defects
Flatness limits and checks are explained in large slab flatness tolerance.
- Centre bow, edge curvature or twist, which cause lippage on floors and walls and gaps on worktops.
- Size or squareness errors, which make joints run off line across a wall.
- Thickness variation across the slab or between slabs, which shows at worktop joints and edges.
Surface and print defects
Shade control is covered in tile shade variation.
- Shade differences between slabs from different batches, or within one batch where sorting was weak.
- Print lines or banding, often from a blocked printer nozzle, running along the slab.
- Smudges, colour spots or missing ink.
- Pinholes and small glaze bubbles, which show most on polished and dark slabs.
- Polishing marks, haze or uneven gloss on polished finishes.
- Scratches from handling or packing without face protection.
Edge and body defects
- Chipped corners and edges, the most common transit damage.
- Hairline cracks, sometimes from firing, sometimes from handling, which may only show when the slab is lit from the side.
- Edge colour bands on standard-body slabs where a full or colour-matched body was ordered.
- Laminations or weak layers in the body, usually only visible when the slab is cut.
Matching and packing defects
- Book-matched sets that do not line up, or slabs shipped out of sequence.
- Mixed batches, shades or calibres in one design.
- Wrong or missing labels on frames and crates.
- Loose or damaged packing that has let slabs rub or move.
Which defects matter most
Not every defect matters equally for every use. On a floor, flatness and calibre matter most, because they decide lippage and joint lines. On a feature wall, shade and print quality matter most, because the eye reads the whole surface at once. On a worktop, body type, thickness, cracks and edge chips matter most, because the fabricator cuts and exposes the edges.
Rank the defects for your main use and write the strictest limits for those into your order.
How to keep defects out of your order
Most defects are caught or prevented before loading. Agree a written grade definition and measurable limits for flatness, size and shade. Keep a signed master sample. Then have production slabs inspected under good light before they are packed into the container.
Our guide on inspecting slabs before loading gives the method. The general tile list is in common floor tile defects.
Next step
We inspect slabs against your specification and the approved sample before loading and report every defect with photos. To set up inspections for your slab orders, book a free sourcing review.