Mineral surfaces are durable, not invulnerable — and their failure modes are all water-borne:

Freeze-thaw spalling: water in pores expands ~9% on freezing; enough cycles scale the surface off concrete, flake brick faces, and crumble mortar joints. Staining and soiling: open pores drink oil (driveways), tannins, rust, and grime that surface cleaning can't reach. Efflorescence: water migrating through masonry carries salts that bloom white on the face. Biological growth: damp porous surfaces feed algae and moss, which hold more damp. Rebar corrosion: in reinforced concrete, chloride-laden water (de-icing salt, coastal air) reaching steel is the structural end-game. Dusting: weak slab surfaces powder under traffic.

Sealing intercepts the common cause — water in the pores — either by repelling it at the surface (penetrating sealers) or barricading it (film sealers). The economics track exposure: a sheltered interior block wall may genuinely never need sealing, while an exposed driveway in a frost-and-salt climate, a stained patio, or a brick chimney taking wind-driven rain each repay the treatment many times over. 'Forever' concrete exists — it is mostly the concrete whose water was managed, by detail design, by luck, or by a sealer.

The fundamental fork in mineral sealing:

Penetrating sealers (impregnators) — silanes, siloxanes, and their blends — soak in and chemically line the pores, making the material repel water while staying vapour-open (the wall still breathes moisture outward). Appearance is unchanged: no gloss, no film, nothing to peel — and no film problems ever: UV-immune, foot-traffic-immune, renewed by simply re-applying years later. Their limit: they repel liquids but leave the surface texture exposed, so they resist stains rather than sealing against them absolutely, and they add no sheen for those who wanted one.

Film-forming sealers — acrylics, polyurethanes, epoxies — lay a continuous coat on the surface: gloss or satin 'wet look' colour enhancement, genuine stain/chemical barriers, and a sacrificial wear layer. Their costs are film costs: they can peel or whiten if moisture pushes from behind (the classic driveway-sealer failure), wear in traffic lanes, may yellow (cheap acrylics) outdoors, and commit you to recoat cycles.

The selection principle: breathable walls and frost-exposed exterior masonry want penetrating repellents almost always; decorative concrete wanting the wet look, interior floors, and stain-critical surfaces justify films — specified UV-stable outdoors and moisture-tested underneath. Where both virtues are needed, hybrid regimes exist: impregnate first, film over, accepting the film's maintenance in exchange for its looks.

By duty:

Driveways (concrete or block paving): the enemies are oil drips, tyre scrub, frost, and — on block paving — joint-sand loss and weeds. Penetrating repellents handle frost and moisture invisibly; purpose-made driveway sealers (typically tough acrylics or PU) add stain resistance and, on block paving, bind the joint sand — the main reason block drives get sealed. Film products here must be breathable-rated or applied to properly-dry substrates, or winter moisture whitens them from beneath. Hot-tyre-rated formulations matter on dark surfaces.

Patios: frost protection plus stain-and-biology management with looks on show. Impregnators for natural, no-change protection (the default on stone-look and riven products); colour-enhancing 'wet look' sealers where deepened tone is wanted — always tested on a spare slab, since enhancement is effectively permanent. Slip: any gloss film on smooth slabs wants an anti-slip additive.

Garage floors: interior, oil-prone, tyre-loaded — the natural home of film systems: epoxy/PU coatings (covered in their own category) for full protection and colour, or a clear concrete-rated sealer as the budget dust-and-oil answer. Bare-minimum garages at least take a penetrating densifier-sealer to stop surface dusting.

Universal preconditions across all three: cured concrete (28 days new), genuinely clean (degreased, de-mossed, efflorescence removed), dry per product, and a test patch — mineral surfaces vary more than tins assume.

Application is a saturation exercise for impregnators, a coating exercise for films:

1. Clean to mineral: wash off grime, strip biology with a masonry biocide, remove efflorescence (dry brushing/specialist cleaner), degrease stains — sealers lock in whatever they cover. Let the surface dry properly (typically 24–48 h; impregnators tolerate slightly damp, films punish it).
2. Penetrating sealers: flood on by low-pressure sprayer, roller, or brush to visible wet saturation, working top-down on walls; many specify a second 'wet-on-wet' pass within minutes. Wipe off surplus pooling on dense surfaces. No film means no lap marks — the forgiving family.
3. Film sealers: thin, even coats with roller or sprayer, two typically, respecting recoat windows and avoiding puddles in texture (milky spots later). Mask everything adjacent — dried film sealer on glass and frames outstays its welcome.
4. Conditions: 5–25 °C, no rain forecast (films: 24 h; impregnators: usually a few hours), and never onto sun-baked hot surfaces (flash-drying kills penetration).

Longevity: quality silane/siloxane impregnators protect 5–10+ years on walls (verify by water-spray beading, re-apply when absorption returns — no removal ever needed). Exterior film sealers realistically run 2–5 years on trafficked surfaces before recoat; interior films longer. The maintenance asymmetry is the quiet argument for impregnators wherever their invisible protection satisfies the brief.

Sealing helps with the outside-in problems and must NOT be misapplied to the inside-out ones:

Rain-driven damp through porous masonry — yes. A breathable penetrating repellent (silane/siloxane, or the newer masonry protection creams) on exposed brick, block, and render dramatically cuts wind-driven-rain absorption while letting the wall exhale vapour — the correct chemistry for soggy exposed gables, chimneys, and parapets, and a standard energy-efficiency measure (dry walls insulate measurably better). Critically, breathability is non-negotiable on solid walls: filming an old wall with non-breathable coating traps internal moisture and accelerates the very decay it was meant to stop.

Efflorescence — partially. The white salt bloom needs water moving through the masonry; a repellent that stops rain ingress starves the mechanism from the weather side. But salts driven by ground moisture rising, leaks, or condensation continue regardless — remove existing bloom first, fix the water source, then seal against re-wetting from rain.

Salt (chloride) damage to reinforced concrete — preventively, yes: silane impregnation is an established highway-engineering defence against de-icing and marine chlorides reaching rebar. Already-corroding structures need repair first; sealing is protection, not remediation.

What sealing cannot fix: rising damp and condensation. Ground moisture defeats surface treatments (that battle involves DPC remediation and drainage), and condensation damp is a ventilation/insulation problem wearing damp's costume. The diagnostic discipline — where is this water coming from? — decides whether the sealer aisle is the solution or an expensive way to hide the symptom for one season.

Impregnators — no. Penetrating repellents leave the surface texture untouched: a riven slab, brushed concrete, or brick face grips identically before and after. This is a genuine advantage of the family and the reason exposed paving defaults to it; the water beading looks slick and isn't.

Film sealers — yes, credibly, and manageably. A gloss acrylic or PU film smooths micro-texture: sealed smooth concrete, dense pavers, and polished stone can become measurably more slippery wet — the classic 'beautiful wet-look patio, treacherous November' complaint. The management toolkit:

1. Anti-slip additives (fine polymer bead or grit) stirred into the final coat — near-invisible insurance, standard practice on outdoor films (the same logic as anti-slip floor coatings generally).
2. Matt and satin formulations rather than full gloss — less film smoothing, less visual slickness, better ageing.
3. Zone the sheen: wet-look on the display areas, additive-loaded or impregnator-only on steps, falls, and walk lines — steps deserve the conservative choice always.
4. Keep films clean: algae on any sealer is the real slip hazard; sealed surfaces actually resist the biology better, provided falls drain and cleaning is periodic.

Buying rule: for any exterior film on a walked surface, treat an anti-slip measure as part of the specification rather than an optional extra — the additive costs cents per square metre, and its absence is what turns a sealing upgrade into a liability.

Diagnose first — the failure names the fix:

Whitening/clouding under a film = moisture beneath (or UV breakdown in cheap acrylic): localised blush sometimes re-flows with solvent (xylene on acrylics — the classic driveway-sealer first aid), but widespread whiteness means the film must go. Peeling and flaking = adhesion gone: stripping time. Simple dullness/wear lanes on sound film = the easy case — clean thoroughly and apply a maintenance coat of the same chemistry (acrylic over acrylic; never trap incompatible layers).

Stripping films: chemical sealer strippers matched to the resin (solvent-based for acrylics; methylene-free modern strippers for tougher films), dwell, scrub, rinse — repeat for multi-coat histories; mechanical routes (diamond grinding, media blasting) for epoxies and big areas, which also re-profiles for whatever comes next. Test patches tell you the chemistry and the labour honestly before the whole driveway commits.

Impregnators never need this ritual — they fade to absorbent and simply re-apply after cleaning: no film, no stripping, the lifecycle argument completing itself.

Renewal strategy after stripping: the moment of bare, clean, profiled surface is the cheap decision point — many owners who stripped a failed wet-look film twice choose the impregnator (or an impregnate-plus-breathable-film hybrid) the third time. Whichever path: fix the moisture story that killed the last film (drainage, falls, rising damp from below the slab), because sealers repeat their history when the substrate keeps its habits.