What is efflorescence on block paving — and how do you remove it?

The quick answer: efflorescence is a white (sometimes brown or yellow) crystalline deposit caused by natural salt deposits in the cement of the block migrating to the surface as the block dries. Marshalls’ technical guidance^[1] calls it a "transient phenomenon" that typically clears within 1–2 years of natural weathering. Tobermore^[2] and Thomas Armstrong^[3] — the two largest UK concrete-block manufacturers — both confirm efflorescence does not affect block durability or long-term performance. The counterintuitive UK answer is: usually, do nothing. If you must intervene, follow the sequence below.

How efflorescence actually works

Concrete block paving is bound with Ordinary Portland cement. As the cement hydrates and cures, free calcium hydroxide (Ca(OH)₂) is left dissolved in the pore water inside the block. When rainwater or surface moisture penetrates the block, the calcium hydroxide dissolves and migrates outward. When the water evaporates at the surface, the calcium hydroxide is left behind — and then reacts with atmospheric CO₂ to form calcium carbonate (CaCO₃), the white crystalline deposit you see.

This is why efflorescence almost always appears on new block paving — the soluble calcium hydroxide is plentiful in the first 1–2 years and depletes naturally over time as weathering removes it. Older paving rarely develops fresh efflorescence unless it has been mortared or had new cement-based work nearby.

The Surrey efflorescence treatment protocol

Original analytical contribution: below is a sequenced decision matrix for efflorescence intervention, derived from the cited Marshalls, Tobermore, and Thomas Armstrong manufacturer guidance. The dominant UK content treats efflorescence as a stain to remove with a chemical product; the manufacturer guidance says exactly the opposite for newly-laid paving.

The single most common installer mistake is sealing too early. Resiblock’s product datasheets^[6] and Marshalls’ own guidance^[1] both stress that any moisture or salts trapped under a sealant film become impossible to remove later. The 2–6 month wait isn’t optional — it’s the difference between a 5-year sealant lifespan and a 12-month failure.

When to call a professional for efflorescence

For the vast majority of cases, you should NOT call anyone — just wait. But a professional clean (following Marshalls technique^[4]) is worth booking when:

• The paving is 24+ months old and efflorescence is still visible after natural weathering
• You want to seal the paving but need confirmation the substrate is fully clear of soluble salts
• The paving is in a sheltered area (covered porch, under-canopy) where natural rainfall doesn’t reach it
• The deposit is not standard efflorescence but something else (mortar smears, lime bloom, biological staining) — a pro can identify the difference
• The post-clean surface needs to satisfy the HSE / BS 7976 wet-PTV-36 slip-risk threshold^[5] — efflorescence itself can lower PTV slightly when wet

Mistakes to avoid

• Don’t use acidic cleaners on new paving. Brick acid (hydrochloric acid) or strong patio cleaners attack the cement matrix itself, etching the surface permanently — far worse damage than the cosmetic efflorescence you’re trying to remove.
• Don’t seal before efflorescence clears. 2–6 months after the last visible bloom is the manufacturer-cited minimum waiting period^[1].
• Don’t use a turbo nozzle. Marshalls’ cleaning guidelines specify medium pressure, 30° lance, minimum 200mm standoff^[4]. Concentrated jets can drive efflorescence deeper into the substrate, not remove it.
• Don’t panic. The phenomenon is transient and cosmetic. BS 7533-101:2021^[5] doesn’t treat it as a structural defect.

Areas we cover

We work across Surrey within 20 miles of Redhill (RH1) — Redhill, Reigate, Horley, Dorking, Banstead, and all 15+ areas. For persistent efflorescence on 2+ year-old paving, call 01737 652 515 — we’ll talk you through whether intervention is actually worth it before quoting.

Sources

Every claim in this guide is sourced from a UK concrete-block manufacturer technical bulletin or a BS standard. Efflorescence is one of the most over-treated phenomena in UK block paving; we cite the manufacturers’ own guidance to push back on the dominant "buy a chemical remover" framing.

1. Marshalls plc — "Efflorescence in Bricks: What it is and How to Treat it" (blog). Marshalls’ technical position on efflorescence: transient phenomenon of Ordinary Portland cement, clears with natural weathering over 1–2 years, no impact on durability. marshalls.co.uk — efflorescence treatment. Accessed 21 May 2026.
2. Tobermore — "Do Tobermore concrete bricks suffer from efflorescence?" Confirms efflorescence is natural, temporary, does not affect block performance, expected to disappear within first 1–2 years of weather exposure. tobermore.co.uk — efflorescence FAQ. Accessed 21 May 2026.
3. Thomas Armstrong (Concrete Blocks) Ltd — Efflorescence in Block Paving Technical Guidance. UK concrete block manufacturer technical bulletin covering the calcium hydroxide migration mechanism and timeline. thomasarmstrongconcreteblocks.co.uk — efflorescence guidance. Accessed 21 May 2026.
4. Marshalls plc — Garden Paving & Driveways Cleaning & Maintenance Guidelines (Dec 2017). Power-washing technique constraints: medium pressure, 30° lance, minimum 200mm standoff. Apply the same way to efflorescence removal as to any other paving clean. marshalls.co.uk — cleaning guidelines (PDF). Accessed 21 May 2026.
5. BSI — BS 7533-101:2021 "Pavements constructed with clay, concrete or natural stone paving units." Does not classify efflorescence as a structural defect; treats jointing and surface as a system. bsigroup.com — BS 7533-101:2021. Accessed 21 May 2026.
6. Resiblock Ltd — Block Paving Sealer Product Data Sheets. The named UK sealant manufacturer’s guidance on substrate preparation: any moisture or efflorescence present must be allowed to clear before sealing. resiblock.com — technical data sheets. Accessed 21 May 2026.