Sealing need tracks porosity and placement, not price:

High-need: the calcium family in service — travertine (naturally holed and thirsty), limestone, honed marble, plus sandstone and porous slates: these darken with a water drop in seconds and drink wine, oil, and grime the same way. In kitchens, bathrooms, and floors they are sealed as a matter of course. Moderate: polished marble (polishing tightens the face; the acid-etch risk remains regardless of sealer — a separate issue), many granites (variable — some absorb oil slowly, some barely at all), quartzite, and dense slates. Low-to-none: gabbro-class 'absolute black' granites, serpentines, and soapstone (protected by its own oiling tradition rather than sealers); and engineered quartz is not stone for this purpose — its resin binder means no sealing, ever.

The one-minute audit that outranks any list: water drop and oil drop (cooking oil) on an inconspicuous spot, wiped after 10–15 minutes — darkening marks absorption, and the speed of darkening ranks the urgency. Placement then weights the verdict: the same limestone that needs annual attention as a kitchen floor needs almost none as a fireplace surround.

And the boundary worth stating early: sealers govern absorption. They do not stop etching — the acid dulling of calcium stones — which is a chemistry problem with its own FAQ. Knowing which of the two an owner fears most is half of choosing correctly.

One family dominates for good reason, with deliberate variants:

Breathable penetrating impregnators — modern fluoropolymer or silane/siloxane chemistry carried into the pores — are the default for effectively all natural stone: invisible, vapour-open (stone must exhale ground and setting-bed moisture or spalling follows), no film to scratch grey or peel, and rated versions repel both water and — crucially for kitchens — oil (check the tin says oleophobic/oil-repellent; water-only sealers under-serve worktops). Solvent-carried impregnators penetrate dense polished faces best; water-carried versions serve most other duties with easier handling.

Colour-enhancing impregnators — same chemistry plus tone-deepening: slate goes charcoal-rich, honed limestone warms, flamed granite saturates. Genuinely handsome and genuinely committing — enhancement does not strip on request — so the test tile is doctrine, viewed dry, in the room's light.

Topical/film stone sealers and waxes: a shrinking niche — high-traffic commercial terrazzo systems, terracotta traditions, some exterior anti-graffiti duties. On domestic stone their films scratch, cloud, and interfere with the stone's own feel; most 'my stone went patchy-shiny' stories start with a topical product on a surface that wanted an impregnator.

Specialist corners: anti-etch worktop coatings (sacrificial films for marble kitchens that accept the maintenance trade), grout-and-stone combined impregnators for tiled fields, and exterior stone repellents shared with the masonry-sealer world.

The purchasing shortcut: a reputable stone-specific, breathable, oil-repellent impregnator — natural or enhancing finish per taste — answers nine stone questions in ten.

The impregnator ritual, done properly once a year or three:

1. Clean to bare stone: pH-neutral stone cleaner (or the maker's deep cleaner for grimed floors), full rinse, and — non-negotiable — complete drying: 24 h typical, longer for thick or freshly-laid stone; impregnators cannot enter water-filled pores. New installations wait until setting beds and grout have released their moisture (installer guidance, often 2–4 weeks).
2. Apply liberally and evenly — pad applicator, sponge, or brush on floors; lint-free cloth on worktops — keeping the surface uniformly wet for the product's dwell (typically 5–15 minutes), feeding thirsty zones so nothing flash-dries.
3. The step that separates professionals: buff off ALL residue before it cures — every trace of surplus wiped with clean dry cloths within the stated window. Impregnator dried on the surface is the smeary haze that gives sealing a bad name (and needs solvent or re-emulsifying with fresh sealer to remove).
4. Second application on absorbent stones, wet-on-wet or per label; dense granites rarely take more than one.
5. Cure: foot traffic in hours, water exposure typically 24 h, full stain performance and worktop food-prep return per label (commonly 24–72 h).
6. Verify with the water/oil drop test once cured; feed any thirsty patches.

Worktop note: choose food-contact-rated stone impregnators for kitchen surfaces — the mainstream stone brands certify exactly this. Floor note: seal yourself out of the room, not into its corner — the oldest joke in the trade survives because it keeps happening.

The most important distinction in stone care, and the one sealer marketing blurs:

Stains are absorption: wine, oil, or rust enters the pores and discolours from within. Impregnating sealers are built for exactly this — they are highly effective stain defence, buying wipe-up time measured in hours instead of seconds.

Etching is corrosion: acids — lemon, wine, vinegar, fizzy drinks, harsh cleaners — chemically dissolve the surface of calcium-based stones (marble, limestone, travertine, onyx) on contact, leaving dull matte marks that are damaged topography, not embedded colour. Penetrating sealers do not prevent etching: the acid attacks the stone surface the sealer left exposed. A sealed marble worktop shrugs off olive oil and still etches under a lemon slice — both truths at once.

Managing etch-prone stone honestly: habits first (boards, coasters, prompt acid wipe-ups, neutral cleaners only); finish choice second (honed marble shows etching far less than polished — many owners pre-hone kitchen marble and relax); remediation third (light etching polishes out with marble polishing compound; deep etching is a re-honing service); and for owners wanting marble looks without the chemistry, the alternatives are sacrificial anti-etch worktop films (real protection, visible maintenance) or acid-immune stones — granite, quartzite — wearing marble's palette.

The buying takeaway: seal calcium stones for stains and accept an etiquette for acids — or choose stone whose chemistry ignores the lemon. Sellers who promise one product beats both physics are selling the wrong half of the truth.

Guideline bands, then the test that overrules them: kitchen worktops in porous stone 6–12 months (oil exposure is the clock); stone floors in kitchens/entries 1–2 years; bathrooms and showers 1–2 years; low-traffic floors, walls, and fireplaces 3–5+ years; dense granites often 3–5 years even in kitchens; exterior stone on the masonry-repellent cycle (5+).

The water-drop test is the real schedule: drops on the working zones — beside the hob, the sink run, the doorway lane — that darken within a few minutes mean reseal that zone soon. Stone wear is local: the professional pattern is spot-resealing the working strips annually and full-field resealing on the long cycle, which halves product and labour without protection gaps.

What accelerates the clock: steam mops (formally discouraged on sealed stone), non-neutral cleaners (each alkaline degrease or acid descale eats sealer — routine pH-neutral cleaning is sealer preservation), abrasive pads, and outdoors, UV plus rain cycling.

What the renewal costs: almost nothing when caught — impregnators layer over their fading predecessors after a clean and dry, no stripping — versus the stained-then-poulticed-then-resealed cycle of the neglected worktop. Quality premium impregnators honestly stretch every band above (some warrant 5–15 years in residential floors); economy sealers halve them — amortised per year, the premium tier is routinely the cheaper chemistry.

One habit institutionalises all of it: reseal-test day once a year — the same afternoon the grout gets its check — and stone care collapses into minutes.

Stone stains lift by poultice — the technique that pulls discolouration back out of the pores — chosen by stain type:

The method: mix an absorbent powder (kaolin, whiting, even paper towel as carrier) with the stain-appropriate liquid into a peanut-butter paste; spread 5–10 mm thick over the stain plus margin; cover with plastic film taped down; let it work 24–48 h as the liquid dissolves the stain and the drying powder wicks it up; lift, rinse neutral, dry — repeat for stubborn depth. Commercial pre-mixed poultices exist for every category below.

By stain: oil and grease (the kitchen classic) — poultice with a degreasing solution or acetone; organic (coffee, tea, wine, leaves outdoors) — poultice with dilute hydrogen peroxide (12%); rust (planters, metal furniture) — dedicated stone-safe rust remover poultices only, never bare acids; inks and markers — alcohol or acetone poultice; biological (mould, algae) — oxygenated stone cleaners; water rings/mineral marks — often surface deposits: gentle scrub with neutral cleaner or fine 0000 wool on granite, and remember a 'stain' that is actually an etch (dull, not dark) needs polishing, not poulticing.

The rules that protect the stone while you work: identify before treating (wrong chemistry sets some stains), never acid on calcium stones regardless of what the internet suggests for rust, test any product on a hidden spot, and re-seal the treated area once dry — the poultice that lifted the stain also cleaned out the sealer.

And the honest scope line: deep old oil in pale limestone, iron migrating from within some marbles, and large-area discolouration are restoration-professional territory — poultices are superb at incidents, not archaeology. Sealed promptly-wiped stone rarely needs any of this page; that is the sealing economy in one sentence.

Both work well; both shift the specification:

Showers and wet rooms: seal, absolutely — daily soap, body oils, and hard-water minerals are exactly what impregnators intercept, and unsealed honed stone in a shower grimes fast. The differences: use a breathable impregnator rated for continuous wet areas (the standard stone brands state this), because the stone-and-bed system must release the water that showering drives in — filming products trap it into spalling and shadowing; expect the short end of resealing cycles (the wettest wall annually); pair with pH-neutral, hard-water-capable stone shampoo, since limescale removers are acids and acid meets marble badly; and accept that sealing does not stop hard-water crust on the surface — squeegee culture manages that, exactly as on glass. Calcium stones in showers remain a maintenance lifestyle even sealed — slate, granite, and quartzite are the low-effort stone choices where the habit isn't wanted.

Outdoors: patios, copings, and stone furniture take exterior-rated impregnators — UV-stable chemistry, freeze-thaw pedigree, and breathability again non-negotiable over damp ground. Colour-enhancers are popular outside (wet-look permanence on slate and sandstone) with the standard test-first commitment; anti-slip is unaffected by impregnators (no film — the texture keeps its rating), which is precisely why impregnators, not glossy topicals, are the outdoor-stone default. Application windows care about weather: dry stone, dry forecast, and shade over baking sun. Cycles run 3–5+ years, verified by the same water test after each spring clean.

The shared principle: wet and weather double down on breathable and penetrating — anywhere water pressure can arrive from behind the surface, films fail and impregnators forgive.