Who this guide is for
- Owners selecting stone for a kitchen, bathroom or hallway
- Anyone who has been offered several stones described as equivalent
- People whose existing stone has dulled, stained or worn along a walking line
- Readers who have been told a sealer will protect a stone and want to know from what
- Anyone about to select slabs at a yard and unsure what to ask
Four vulnerabilities, not one scale of quality
Stones differ along axes that do not line up with one another, which is why a single ranking is impossible. Acid reactivity is one, and it is a chemical property of the minerals present. Porosity is a second, and it governs staining. Hardness is a third, and it governs scratching and burnishing. Direction is a fourth, and it governs how the stone breaks down over time.
The reason the axes matter separately is that they are independent. Hardness tells you nothing about porosity, so a stone that resists scratching can still absorb a spill readily. That single fact explains a great deal of the disappointment in this subject.
- Acid reactivity: a chemical attack on the mineral, not dirt
- Porosity: how readily liquids and colours are taken up
- Hardness: scratching, burnishing and how traffic lines appear
- Direction: bedding planes and cleavage, and how the surface breaks down
The carbonate family and etching
Marble is recrystallised limestone, and both are carbonates: lemon juice, vinegar, wine and many household cleaning products dissolve a little of the surface and leave a dulled mark. Etching is a chemical change in the stone rather than dirt, so it cannot be cleaned away and is dealt with by refinishing. Onyx behaves the same way, being a direct carbonate precipitate.
Two things follow that are easy to miss. Many everyday cleaning products are mildly acidic, so cleaning choices matter as much as spills. And a honed surface shows etching far less obviously than a polished one, which makes the finish decision as consequential as the stone decision.
The silicate family, and why it is not simply safer
Granite, quartzite and slate are silicates and are not etched by the mild household acids that dull calcite stones. That is a genuine difference and it is not immunity. Granite is dense but not without porosity, and lighter, more open slabs can take up oils and coloured liquids. Quartzite has real porosity that varies enormously between quarries, and it is frequently impregnated by fabricators.
Slate has weaknesses of a different kind again: some slates carry iron sulphide or carbonate inclusions that can rust or bleed at the surface, and because the rock splits along cleavage, damage often takes the form of surface flaking rather than the rounding seen on a granular stone.
Sandstone and soapstone: the two outliers
Sandstone is defined by its natural cement rather than its colour. A silica-cemented bed is a silicate and is much less troubled by acids; a carbonate-cemented bed behaves far more like limestone. The cement has to be identified rather than assumed from appearance, and sandstone is a family rather than a material.
Soapstone is soft enough to be marked by everyday objects, with very little open porosity, so liquids sit on the surface rather than soaking in. Oil or wax is applied for appearance rather than protection. Owners who like it treat the accumulating marks as patina, and owners who expect a pristine surface find the same behaviour unacceptable.
Direction: the vulnerability that is a laying decision
Sandstone was laid down in beds, so units are normally set with the bedding planes horizontal, on their natural bed, so that weathering works across the layers rather than lifting them apart. Face-bedded stone, where the layers stand parallel to the exposed face, is the classic cause of flaking and contour scaling.
That makes it a laying error rather than a stone defect, and it is usually invisible until the surface starts to shell off years later. Bed orientation has to be marked and understood by whoever lays the stone rather than left to the judgement of the moment.
What a sealer actually does, and what it does not
An impregnating sealer is drawn into the pores and leaves the active lining the pore walls rather than bridging them. It slows the rate at which liquids are taken up, which buys time to deal with a spill before it becomes a stain. That is narrower than the word sealer suggests.
It is not a barrier, it does not make a surface stain-proof, and it does not stop acids etching a carbonate stone, because that is an attack on the mineral rather than on the pores. Etching and staining are different problems and only one of them is affected by a treatment. Cleaning products bought later can undo the treatment quietly.
Naming is unreliable, and that is a selection risk
Trade names for stone are not standardised, and the word granite in a slab yard may cover a related igneous stone. Material sold as quartzite is sometimes dolomitic marble, and the seller may believe the name in good faith. Building onyx and gemstone onyx are different materials entirely.
The response is to ask the supplier to state the rock type in writing rather than accepting the marketing name on the slab rack, and to ask for the quarry and bed name with the supplier's own technical information for that bed. A sample tile also rarely represents the figure and ground colour of the slab that will be installed.
Start from the room, then look at slabs
The useful order is to write down what the room actually presents — acidic spills, oils, abrasive grit walked in from outside, standing water, dragged furniture, the cleaning products the household really uses — and take that list to the yard. A stone is then selected against a known exposure rather than against a photograph.
Expectations belong on the same list. Whether a patina is welcome or unacceptable is something to settle before ordering, because several of these stones will change whatever anyone prefers, and refinishing a stone floor is disruptive work that generally needs the room emptied first.
Selecting stone against the risks a room presents
- 1Write down what this room actually spills, drops, drags and walks in
- 2List the cleaning products the household really uses, not the ideal ones
- 3Ask the supplier to state the rock type in writing, not the marketing name
- 4Ask for the quarry or bed name and the technical information for that bed
- 5For sandstone, establish which natural cement binds it
- 6Ask whether the slab contains softer or soluble mineral seams
- 7Decide the finish as deliberately as the stone, since honed and polished differ
- 8Ask whether any treatment is intended, by whom, and what it is expected to slow
- 9Establish that etching and staining are different problems in this room
- 10Ask about bed orientation and who marks it before laying
- 11Select slabs in person where the figure and ground colour matter
- 12Settle whether a patina is welcome before ordering rather than after
- 13Ask what repair and refinishing would involve for this particular stone
Common mistakes to avoid
- Assuming hardness implies imperviousness, when porosity and hardness are separate
- Expecting a sealer to prevent etching, which is an attack on the mineral not the pores
- Accepting a trade name at the slab rack as a statement of what the rock is
- Choosing a polished finish where a honed one would hide etching far better
- Judging a natural material from a small sample rather than the actual slab
- Laying a bedded stone face bedded, which shows years later as shelling
- Using everyday cleaning products that are mildly acidic on a carbonate surface
- Treating an accumulating patina as a defect in a stone that was always going to change
When to involve a professional
- The quarry or supplier's technical information for the exact stone and finish governs its use, since two stones sold under similar names can behave very differently
- Whether a floor or wall can carry the weight of stone is assessed by a qualified professional
- Which surface treatment suits a particular stone, and when it is applied, follows the supplier's guidance for that stone
- In wet rooms and shower construction, the waterproofing and drainage design governs and belongs to a qualified professional
- Whether an existing stone surface can be refinished, and how, is a specialist judgement made at the building
Frequently asked questions
Questions readers ask about this topic
What is the difference between etching and staining?
Etching is a chemical change in the stone where an acid has dissolved a little of the surface, and it cannot be cleaned away; it is dealt with by refinishing. Staining is a substance taken up into the pores. A treatment that slows staining does nothing about etching.
Does a sealer make stone stain-proof?
No. An impregnator lines the pores rather than blocking them, slowing the rate at which liquids are taken up so there is time to deal with a spill before it becomes a stain. The word sealer leads owners to expect a barrier, which is not what the product provides.
Is quartzite always harder and safer than marble?
Genuine quartzite is a silicate and is not etched by household acids, which is a real difference. It still has porosity that varies enormously between quarries, and softer mineral seams within a slab show wear first. A great deal of material sold as quartzite is also something else.
Why did my sandstone paving start flaking?
That pattern is often face bedding, where the layers stand parallel to the exposed face instead of horizontal. It is a laying error rather than a stone defect, and it is usually invisible until the surface starts to shell off years later.
Which stone is best for a kitchen?
No page can answer that for your kitchen, and the useful version of the question is the reverse. Write down what that kitchen actually presents — acids, oils, grit, dragging, the cleaning products used — and take that to the yard, where slabs are selected against a known exposure.
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