Sintered Stone Slabs: Writing a Fabrication Brief Your Cutter Can Actually Follow

Every buyer asks the same four things about sintered slabs: price per square metre, thickness, lead time, and whether you can ship with the furniture. The questions that actually decide whether the project goes well are different, and they mostly live in the room where the slab gets fabricated — which in most cases is not the plant that made it.

I've watched slabs come off a very good Guangdong line, get crated immaculately, cross an ocean without a scratch, and then get destroyed by a fabricator with a dull blade and a lazy saw table. The material was fine. The purchasing decision was fine. The gap was in the brief.

What you're buying, briefly

Most "sintered stone" on the market is a pressed and fired ceramic slab — clay, feldspar, silica, pigments, no resin — fired around 1200°C at high pressure. Different from quartz composite, which is resin-bound and heat-sensitive, and different from natural marble, which is soft and porous. The Chinese trade term is 岩板 (yánbǎn), literally rock slab, and the naming has become loose enough that you should ask for the technical data rather than the marketing category.

The numbers that matter: water absorption under 0.1%, bending strength usually quoted between 45 and 60 MPa depending on the producer and thickness, and a Mohs hardness in the 6–7 region. These are sensible levels and broadly consistent across the better producers. What varies is consistency — same nominal spec, different batch, and the flatness moves.

Thickness is a specification, not a price lever

The same design will be sold at 6, 9, 12, 15 and 20 mm. Buyers grab 6 mm because it's cheaper and because the freight maths looks better, then discover that 6 mm cannot take a 45 mm mitre joint properly, can't span a 600 mm cabinet without a substrate, and needs a full support base on countertops.

Rough rule from the fabricators I trust: 3 mm and 6 mm for wall cladding and cabinet doors, bonded to a substrate; 12 mm for countertops where you want a mitred edge; 20 mm where the design calls for a chunky visible edge or the slab is being used as an island top with a waterfall. Carting 20 mm around a site is a two-person job and worth it only if the design needs it.

One concrete consequence of getting this wrong: a 3200×1600 slab at 20 mm weighs roughly 150 kg. That is past the point where two men move it comfortably, past the point where a standard A-frame on castors is safe, and past the point where "we'll just carry it up the stairs" is a plan. If you're buying 20 mm into a retrofit, price the lifting equipment or buy 12 mm.

Cutting: where most of the loss happens

Wet cutting only. The blade matters — a continuous-rim diamond blade designed for dense, hard porcelain, not a segmented blade for concrete and not a marble blade. Feed rate wants to be slow: around 1.5 to 2 m per minute on a bridge saw. Push a dull blade fast and you get chipping on the exit edge and, worse, micro cracks that surface as a crack three weeks after installation in a heated kitchen.

Ask your fabricator two questions before they touch a slab. What blade are they running and when was it changed? And what's their water flow? A fabricator who changes blades on a slab count rather than "when it feels slow" is a fabricator who's done this before.

Chipping tolerance should be written down. On a visible polished edge, chips over 1 mm are a reject; over 2 mm on an internal cut covered by trim is acceptable. If you don't write it, you'll get a top edge with a 3 mm nick and a conversation about "the material's fault."

Cutouts: the numbers that stop a countertop from cracking

This is the part of the brief most often left to the fabricator's judgment, and where the failures come from.

• All internal corners of a cutout need a radius. R5 minimum, R10 is safer. A square internal corner is a stress riser and it's where cracks start.
• Distance from the edge of a cutout to the edge of the slab: 50 mm minimum, 80 mm preferred on a sink that's being used hard.
• Distance between two cutouts (hob and sink, for instance): at least 100 mm of material between them.
• Hob cutouts get a heat-isolation strip and, on 12 mm, a reinforcement frame if the span exceeds 500 mm.

If your design puts a sink close to a wall edge on a narrow counter, the geometry may simply not work in 12 mm, and you should find that out at the drawing stage, not on site. Ask the fabricator to redline the shop drawing against these numbers and send it back. It takes an afternoon and saves the whole job.

Book-matching: the order of operations nobody explains

Book-matched slabs — mirrored veining, the look that makes a slab wall look like an open book — have to come from the same block and be cut as a pair at the plant, with matching serial numbers marked on the crates. You cannot book-match after the fact by buying two slabs of the same design code. The veining won't correspond and it will look like a mistake.

The practical instruction for the purchase order: request book-matched pairs by serial number, photograph the pair together at the plant before packing, and get the serial numbers into the packing list. When the container arrives, match serial numbers on the crate to the list before the fabricator cuts anything. Once cut, the pairing is gone.

Second point: colour and veining vary across production batches on the same design code. A job needing 20 slabs should come from one batch, or the client should accept a visible shift in a seam. Most plants will tell you this if you ask; few will volunteer it.

Transport: the pallet that costs you the job

Slabs ship vertically. Always. A-frame crates, strapped, with foam or cork between slabs. Horizontal stacking of large-format slabs in a container is how you get a crack running from one corner, and it will be blamed on the material.

Three things to check on the loading photos: the slabs standing on their long edge, not their short edge; a wooden spacer between every slab or every other slab with sufficient thickness; and the A-frame feet secured to the container floor. Then check the truck that takes them from port to your fabricator — a lot of damage happens in that last 50 km on a flatbed with the crate resting on its back.

Then, at the fabricator: never store slabs flat on a floor, even briefly. Never let anyone lean one against a wall at 10° and walk away. A 3200 mm slab leaning at a shallow angle is a 150 kg lever waiting for a footstep.

What to ask before you order

Ask for the batch technical report covering water absorption, bending strength and stain resistance for the exact thickness you're buying — thickness affects strength and reports are often issued only for one. Ask for the flatness value at the plant, not on the datasheet. Ask who fabricates for you and whether they've worked with this material before; if the answer is "the installer will figure it out," either find another installer or buy a smaller format.

Sintered slab is a good material and it solves real problems — big, thin, hard, non-porous, no resin to yellow. It also punishes cheap decisions in the last two steps of the chain far more than in the first. The plant price is maybe 40% of the installed cost. The other 60% is blades, skill, crates and patience, and that's where your project actually lives.