Can I patch repair cement on lime with more cement?

Strongly discouraged — perpetuates damage cycle. Best practice: rake out cement carefully (avoid further face damage), repoint in matching lime spec, replace any spalled bricks with salvaged matching London stock. Cost more upfront than further cement patch but stops face loss progression. SPAB + Historic England technical guidance unanimous on this.

What is hot lime + when do I use it instead of NHL?

Hot lime / lime putty = quicklime slaked on site + matured into putty for 3+ months before use. Soft, breathable, self-healing micro-crack closure. Used on pre-1850 buildings + best-heritage Grade I/II* listed where authenticity demanded. Slower set + cure than NHL — programme +30–50%. £40–£60/m² premium over NHL. Specialist contractors only (Cliveden Conservation, Pavilion Plaster, Owlsworth IJP).

How do I tell if my mortar is lime or cement?

Visual: lime is pale cream/off-white, soft (can score with screwdriver), often with sand visible; cement is grey/dark grey, hard (cannot score), uniform texture. Chemical test: drop dilute HCl on small sample — lime fizzes + dissolves, cement fizzes lightly + powder remains. Mortar analysis by Stone Federation member £180–£280 sample for definitive composition + recommended replacement spec. Builderr routine spec gate on pre-1919 jobs.

Lime Mortar vs Cement London Brickwork | Builderr

Lime Mortar vs Cement Pointing — London Heritage Brickwork

Pre-1919 London solid-wall houses (Georgian, Victorian, Edwardian) require lime mortar — NHL 2 or NHL 3.5 hydraulic lime, or hot-lime mix for pre-1850 stock. Cement mortar (1920s+) is too hard, traps wall moisture inside soft handmade brick + causes spalling, salt damage, irreversible face loss. Lime pointing cost £85–£180/m² depending on scope. LBC + most CAs mandate lime. Cement on pre-1919 brick = enforceable damage.

Why lime not cement on pre-1919 stock

London pre-1919 buildings constructed with soft handmade bricks (Smithfield stocks, London stocks, gault clays) bedded in lime mortar that breathes — moisture wicks through mortar joints + evaporates from surface. Cement mortar (introduced 1920s, dominant 1950s+) is harder than soft handmade brick — moisture cannot evaporate through cement so concentrates in adjacent brick face, freezes in winter, salts crystallise, brick face spalls + disintegrates over 5–25 years. SPAB + Historic England + English Heritage research consistent: cement pointing on solid-wall pre-1919 housing causes irreversible damage. Visible signs: spalled brick faces with cement joints proud (originally flush); rust streaks below cement; powdered brick at base of wall; rising damp readings false-positive due to trapped moisture. Lime mortar specification: (1) Natural Hydraulic Lime (NHL) — NHL 2 for soft Victorian/Edwardian stock + sheltered elevations; NHL 3.5 for harder bricks + exposed elevations + chimneys; NHL 5 rare in domestic, used for hard cappings only. Mix 1:2.5–1:3 lime:well-graded sharp sand. (2) Hot lime / lime putty — quicklime mixed on site to putty, matured 3+ months, used for pre-1850 buildings + best heritage practice. (3) Pre-mixed lime — Ty-Mawr, Lime Green, Anglia Lime — bagged ready-mixed convenient option, £18–£32/25kg. Joint profile must match original — flush, weatherstruck, or recessed depending on era + house style.

Cost + LBC enforcement + repointing scope

London lime repointing rates 2026: (1) Full repointing rear elevation 2-storey terrace ~75–95m² — £8,500–£16,500 + scaffold £2,200–£3,800. (2) Front elevation per linear metre joint £24–£42. (3) Per m² rates £85–£140 NHL standard, £140–£180 hot-lime/lime-putty heritage spec. (4) Chimney repointing (above roof) £1,400–£3,200 per stack including scaffold + drone survey. (5) Brick replacement (decayed faces) £85–£180 per brick supplied + fitted matching salvaged London stock. Programme: full elevation 2–4 weeks dry weather; chimney 3–7 days. Lime cure conditions: above 5°C, below 30°C, no rain forecast 48 hrs, no direct sun (hessian cover); Oct–March work limited. LBC + CA enforcement: cement-mortar repointing on Grade II listed = LBC breach + criminal offence; LPAs (Westminster, Camden, K&C, Tower Hamlets) actively enforce + require remedy. CA enforcement variable but rising. Insurance + selling: cement-on-pre-1919 increasingly flagged by surveyors on Homebuyer Reports + Building Surveys — lime spec is mortgage + insurance friendly. VAT: 0% on LBC repair on Grade I/II* listed; 20% on standard. Builderr practice: pre-1919 + every CA-located house defaults to lime spec — cement requested in writing only if owner insists despite warning + record retained.