Sealed or unsealed: what a sealer actually protects.
A pale ring on a bench, a dark patch on travertine after a spill: the difference between the stone that wipes clean and the one that soaks up the mark is usually a sealer. Here is exactly what it does and does not buy you.
Natural stone has pores, fissures and mineral variation, and even a polished face is more absorbent than it looks. Unsealed, there is nothing between a spill and the pores. Sealed with a penetrating product, the pores are lined from inside and the spill sits on top long enough to be wiped. The operative word is slows.
What changes
Absorption. Oil, wine, coffee, cosmetics and dirty mop water take longer to get in, so a five-minute spill becomes nothing and cleaning stays on the surface where it works. Light stone stays even in colour instead of collecting shadows around the sink. And a restoration lasts longer, because the freshly honed and polished stone is protected from the first day.
What does not change
Etching. Acid reacts with the calcium at the face of the stone, above the sealer, so lemon juice dulls a sealed marble bench exactly as it dulls an unsealed one. Scratching, lippage, dullness and existing stains are also untouched. A sealer is not a shine and not armour.
Which stones need it most
Travertine and limestone, which are open and absorbent and often used in wet areas. Honed marble, whose matte face shows darkening from oils readily. Grout, which is more porous than anything beside it. Polished marble still benefits for stain resistance. Dense granite may need little; porcelain generally needs none, though its grout lines do. Terrazzo depends on its binder and any existing coating, and engineered stone is a different question again.
The test, and its limit
A few drops of water on a clean dry spot for ten minutes: beading means protected, darkening means due. It measures water absorption only. It does not reveal oil resistance, contamination, a failing coating, previous treatments or etching, and it cannot tell you whether the surface needs cleaning, honing or a different product. Blotches, dull lanes, recurring stains, peeling and a sticky feel after cleaning are all reasons to have the surface looked at before anything goes on it.
When sealing is the wrong first move
When the stone is already dull, etched, scratched, cracked or stained. Sealing over contamination locks it in and gives a patchy result; sealing over damage protects the damage. The sequence is assess, clean, correct, then seal on clean dry stone. Sealer chosen for a dense polished vanity is wrong on a textured travertine floor, and an enhancing sealer that deepens colour is a permanent decision on light stone, so the product is matched to the surface and tested first.
Afterwards the care is the same as ever: a neutral cleaner, spills wiped, no acids, coasters and boards on benches, mats at doors. Reseal when the water test says so, not when the calendar does.
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Related questions.
How often should marble be sealed?
It depends on the surface and what it takes. A kitchen benchtop or a shower, which see acid, oil and water daily, are usually resealed every twelve months. A floor or a table in a lower-traffic room goes two years or more. The honest test is the water bead: a few drops left on the stone for ten minutes should sit up. If they soak in and darken the stone, the sealer has worn and it is time. We add every surface we seal to a reminder list and message you when yours is due, so you do not have to remember. A sealer is not a coating sitting on top. A penetrating sealer soaks into the stone and slows how fast liquids get in, which buys time to wipe a spill before it becomes a stain. It does not stop etching, because acid attacks the surface of the marble itself rather than soaking into it, and nothing short of changing the stone prevents that.
I do not know what kind of stone I have. Does that matter?
Not for getting a quote. Send a photo and we can usually tell, and the difference between marble, limestone and travertine changes the method more than the price. If you want to check yourself: marble is usually veined and takes a high polish; limestone is more uniform and often honed; travertine has visible holes; granite is speckled and much harder; engineered stone is uniform with no natural veining and does not etch. A drop of lemon juice on an inconspicuous spot will etch marble and limestone within minutes and do nothing to granite or engineered stone. Wipe it off straight away either way.