Concrete flags divide by how they are made, which predicts how they perform:

1. Pressed (hydraulically pressed) slabs are compacted under high pressure into dense, dimensionally exact units — the classic utility flag and the public-footpath standard. Strong for their thickness, consistent, and the cheapest paved square metre available; the finish palette is functional (natural, buff, charcoal, textured).
2. Wet-cast slabs are poured into moulds, which is what allows decorative faces: riven stone effects, flagstone profiles, slate textures, and colour blends. Marginally less dense than pressed, entirely adequate for patio duty, and the mainstream choice for garden aesthetics on a budget.
3. Reconstituted stone raises the wet-cast recipe with crushed natural stone aggregate and refined moulds taken from real flags — the closest concrete gets to quarried character, at a price still under most natural stone.
4. Textured and exposed-aggregate slabs show decorative aggregate for grip and sparkle — long-lived municipal favourites.
5. Specials: council-pattern tactile flags, shed-base packs, and heavy-duty thick flags for trafficked areas.

Across all types the buying signals are declared strength class and thickness (see the loading FAQ), colour through the body versus surface-only pigment (through-colour hides chips), and whether the range includes matching edging and steps — the accessory question that decides how finished the job looks.

Concrete's case is straightforward: it delivers 80% of the function at 40% of the price — and its limits are just as clear.

Where concrete wins: upfront cost, availability (every merchant, every week), workability (cuts with an ordinary angle grinder, forgiving to lay on standard mortar), replaceability (standard formats stay in production for decades), and honest utility — for a shed base, a bin path, or a rental-property patio, nothing else makes financial sense. Modern wet-cast faces are genuinely attractive at first laying.

Where the premium materials pull away over time: concrete is porous, so it darkens when wet, feeds moss in shade, drinks oil and barbecue fat, and fades — surface pigment lightens over 5–15 years, and the crisp day-one face weathers toward its aggregate. Porcelain holds colour and repels stains permanently; natural stone weathers into character rather than away from it. Concrete also wears at edges and can spall in hard freeze-thaw if a cheap slab meets a wet winter (buy declared freeze-thaw-resistant grades in frost climates).

The honest matrix: short-tenure or budget-led projects, utility areas, and large areas where cost multiplies — concrete, without apology. Forever-home showpiece terraces, pool surrounds, and stain-critical dining patios — porcelain or stone repay their premium. The hybrid many gardens run: decorative wet-cast on the visible patio, pressed utility flags behind the shed — same trade, two budgets, both correct.

Concrete is the most forgiving slab to lay, which makes it the classic first landscaping project — the method:

1. Excavate and sub-base: dig out to firm ground, allowing for 100 mm compacted MOT Type 1 sub-base + 30–40 mm mortar bed + slab thickness, with the finished surface 150 mm below any adjacent damp-proof course. Compact the sub-base in layers with a plate compactor — base preparation is nine-tenths of a flat patio.
2. Set falls: string lines at a 1:60–1:80 fall away from buildings so rain sheds.
3. Bed: lay each slab on a full mortar bed (5:1 building sand:cement, wetter than bricklaying mortar) — resist the five-dab shortcut, which leaves hollow-sounding slabs that crack and rock. Tap down to the line with a rubber mallet; lift and re-bed rather than tapping forever.
4. Damp the backs of very dry slabs in summer so they don't suck the bed dry.
5. Joints: 8–12 mm for riven-effect, 5–10 for smooth formats. Point with mortar (classic), or a brush-in jointing compound for speed — sand alone washes out.
6. Cuts: angle grinder with a diamond blade, outdoors, with dust suppression and PPE.
7. Cure: keep foot traffic off for 24–48 hours.

One material-specific habit: work from several packs at once, because concrete colour varies by production batch just enough to band an unmixed patio — and wash mortar smears off faces immediately, since cement stains cement surprisingly well.

Concrete's open pore structure is the whole story: it drinks water, and everything dissolved or suspended in that water — algae spores, leaf tannins, spilt oil, rust — moves in with it.

The routine that keeps it smart: sweep often (standing organic debris is moss's seedbed), wash each spring with a stiff brush and a dilute concrete-safe patio cleaner, and treat green growth with a proprietary algaecide/biocide that keeps working for months rather than bleaching it white for a fortnight. Pressure washing works well on pressed and smooth wet-cast faces — moderate pressure, wide fan, sweeping motion — but ration it on decorative textured faces, where annual high-pressure blasting gradually erodes the moulded detail and the pointing.

Stain triage: fresh oil — absorb immediately (cat litter, sand), then degrease with a concrete degreaser; old oil needs poultice products and patience. Rust from furniture responds to concrete-safe rust removers (not raw acid on coloured slabs, which can etch pigment). Efflorescence — the white bloom on new slabs — is lime migration, normal, and best left to weather off over a season; acid-washing it early often makes patchwork.

Prevention worth its price: an impregnating concrete sealer applied to a clean, dry, cured patio slows the drinking dramatically — oil beads instead of soaking, green growth wipes off — refreshed every 3–4 years. On a decorative patio it is the difference between weathering gracefully and weathering visibly; on the bin path, nobody bothers, which is also correct.

Formats: the traditional council module is 600×600 mm, with 450×450 the garden-centre staple, 600×300 and 400×400 as companions, and mixed-size 'patio packs' (typically four sizes laid to a repeating random pattern) driving the decorative market. Larger wet-cast formats to 900×600 exist; concrete's weight (a 600×600×38 flag is ~30 kg) sets the practical handling limit.

Thickness and duty:

• 32–38 mm — standard garden patio and path grades; fine for all pedestrian use on a proper full mortar bed.
• 50 mm — heavy pedestrian and occasional light vehicle crossings (on an appropriate base); the traditional public-footpath spec.
• 60–70 mm+ pressed flags — trafficked and public-realm duty on engineered bases. For regular car traffic, the better concrete answer is usually block paving (60–80 mm blocks), engineered exactly for wheels; large flags under cars crack at corners unless the base is genuinely rigid.

Point loads deserve respect: hot tubs, large planters, and trampoline legs concentrate weight — spread them on pads, and check a slab patio over a soft base before parking a 1,500-litre hot tub on four feet.

The load truth every failure teaches: the slab is rarely what breaks — the bed and base are. A 38 mm flag on full mortar over compacted Type 1 outperforms a 50 mm flag on dabs over topsoil every time. Buy the declared strength class for the duty, then spend the real attention underneath it.

Yes — concrete is the most renovation-friendly paving there is, and a tired patio has four escalating options:

1. Deep clean + re-point. The step most patios actually need: patio cleaner, brush or measured pressure wash, moss treatment, then rake out and renew failed pointing (brush-in compound modernises the look in an afternoon). Often the 'new patio' was under the dirt all along.
2. Seal. On the clean, dry surface, an impregnating sealer revives colour depth slightly ('damp look' versions deepen it deliberately) and slows future staining — the maintenance reset button, redone every few years.
3. Paint or coat. Dedicated patio and concrete floor paints (water-based acrylics for pedestrian gardens; more durable resin coatings where budget allows) transform colour completely and are the honest answer for mismatched or stained-beyond-cleaning slabs. The realism: surfaces must be clean, sound, and dry; expect re-coating every 2–5 years as wear paths appear; and choose anti-slip formulations or additives — a painted smooth slab in rain is an ice rink. Landlords and quick-sale refreshes lean on this route heavily.
4. Overlay or replace selectively. Standard formats' long production lives mean single cracked slabs can often be swapped like-for-like (the spare-pack habit pays again); and where the base is sound, thin porcelain or resin systems can overlay a concrete patio entirely — the base concrete becoming the substrate for its own upgrade.

The framing: concrete paving is infrastructure with a cosmetic layer. The infrastructure usually outlives several cosmetic generations — renovate the layer that failed rather than excavating the one that didn't.

Slip: concrete's default texture is naturally grippy — pressed flags and textured wet-cast faces test well wet, which is why public footpaths are made of them. The exceptions are smooth power-floated or heavily-sealed faces, worn-glassy old flags, and any slab wearing an algae film — the biology, not the material, causes most concrete slips. Practical spec: choose textured or riven-effect faces for wet zones and slopes, keep the surface clean, and if painting or gloss-sealing, use anti-slip versions. For steps, pick purpose-made textured step units with defined nosings.

Frost: quality concrete slabs from reputable makers are produced with air-entrained, low-absorption mixes and declared freeze-thaw resistance (marked to the paving standard's weathering class) — those flags shrug off decades of freeze cycles; Nordic and alpine towns are paved with them. Failures — surface spalling, flaking faces after a hard winter — trace to economy imports without the weathering declaration, slabs standing in ponded water (missing falls, blocked drainage), and hard de-icing salt use on marginal slabs.

The winter care rules: maintain falls so slabs drain, prefer grit or paving-safe de-icers over generous rock salt on decorative faces, and let the datasheet promise frost resistance rather than assuming it — the declaration costs nothing to check at purchase and everything to discover missing in March. Combined with the slip habits above, a well-chosen concrete patio is one of the safest, most weather-indifferent surfaces a garden can wear.