Brickwork and Pointing Guide for London Homes

LONDON STOCK BRICK IS A KILN-FIRED CLAY BRICK PRODUCED FROM THE YELLOW BRICKEARTH FOUND ACROSS THE LONDON BASIN. ITS DISTINCTIVE YELLOW-GREY COLOUR AND IRREGULAR SURFACE TEXTURE COMES FROM THE INCLUSION OF CHALK AND COAL ASH (BREEZE) IN THE BRICK MIX, WHICH FIRED IMPERFECTLY IN TRADITIONAL SCOTCH KILNS. THE RESULT IS A RELATIVELY SOFT BRICK (COMPRESSIVE STRENGTH 10-15 N/MM2 — COMPARED WITH 35-70 N/MM2 FOR MODERN ENGINEERING BRICKS) WITH MODERATE POROSITY (12-20% WATER ABSORPTION). THE KEY IMPLICATION OF THESE PROPERTIES IS: LONDON STOCK BRICK IS SOFTER AND MORE POROUS THAN MODERN BRICK. THE MORTAR USED IN JOINTS MUST ALWAYS BE SOFTER AND MORE POROUS THAN THE BRICK ITSELF — OTHERWISE MOVEMENT AND MOISTURE MIGRATION ARE FORCED INTO THE BRICK FACE RATHER THAN THE SACRIFICIAL MORTAR JOINT, CAUSING SPALLING. ORIGINAL MORTAR IN VICTORIAN LONDON TERRACE BRICKWORK WAS LIME MORTAR — TYPICALLY LIME PUTTY (CALCIUM HYDROXIDE) GAUGED WITH SHARP SAND AND SMALL AMOUNTS OF HYDRAULIC LIME OR NATURAL CEMENT (ROMAN CEMENT). MODERN PORTLAND CEMENT MORTAR (OPC: SAND RATIO 1:3 OR 1:4) IS FAR TOO HARD AND IMPERMEABLE FOR LONDON STOCK BRICK AND MUST NEVER BE USED FOR REPOINTING ORIGINAL VICTORIAN BRICKWORK.

THE CORRECT REPOINTING MORTAR SPECIFICATION FOR LONDON STOCK BRICK FOLLOWS ESTABLISHED GUIDANCE FROM HISTORIC ENGLAND, SPAB (SOCIETY FOR THE PROTECTION OF ANCIENT BUILDINGS), AND BS 4721. THE KEY PRINCIPLES: (1) BINDER — USE ST ASTIER NHL 3.5 (NATURAL HYDRAULIC LIME, FEEBLY HYDRAULIC) AS THE PRIMARY BINDER FOR MOST LONDON REPOINTING. ST ASTIER NHL 2 (VERY FEEBLY HYDRAULIC) FOR EXTREMELY SOFT OR FRIABLE BRICKS. FOR EXPOSED GABLE WALLS AND CHIMNEYS WHERE FASTER STRENGTH GAIN IS NEEDED: CONSIDER ST ASTIER NHL 5 (EMINENTLY HYDRAULIC) IN 1:2.5 MIX. PURE LIME PUTTY MORTAR (NO NHL) IS APPROPRIATE FOR INTERNAL WORK OR VERY SHELTERED POSITIONS. (2) AGGREGATE — WELL-GRADED SHARP SAND IS THE STANDARD AGGREGATE. THE GRAIN SIZE AND COLOUR SHOULD MATCH THE ORIGINAL MORTAR AS CLOSELY AS POSSIBLE — SOME LONDON BRICK SUPPLIERS AND CONSERVATION MORTARS OFFER COLOUR-MATCHED AGGREGATES. MIXES: NHL 3.5: SHARP SAND = 1:2.5 (STANDARD REPOINTING FOR MOST LONDON STOCK BRICK TERRACES). FOR EXPOSED LOCATIONS: 1:2 (NHL 3.5: SHARP SAND). (3) MIXING — HAND MIXING IS PREFERRED FOR SMALL QUANTITIES TO AVOID OVER-WETTING. A SMALL AMOUNT OF LIME PUTTY (1 PART LIME PUTTY TO 1 PART NHL) ADDED TO THE MIX IMPROVES WORKABILITY AND ADHESION IN DIFFICULT CONDITIONS. (4) TOOLING — REPOINTING SHOULD BE FINISHED WITH A FLUSH OR SLIGHTLY RECESSED JOINT (POINT FLUSH, THEN LIGHTLY BRUSHED BEFORE INITIAL SET TO EXPOSE THE AGGREGATE). NEVER USE A STRUCK, BUCKET-HANDLE, OR RODDED JOINT ON LONDON STOCK BRICK — THESE DIRECT WATER INTO THE BRICK FACE.

THE MAIN BRICKWORK DEFECTS IN LONDON HOMES ARE: (1) SPALLING — LOSS OF THE OUTER FACE OF THE BRICK DURING FREEZE-THAW CYCLING. CAUSED PRIMARILY BY: (A) CEMENT REPOINTING TRAPPING MOISTURE IN THE BRICK FACE; (B) OVERSATURATED WALLS (FAILED GUTTERS, FLASHINGS, RENDER) THAT CANNOT DRY OUT; (C) OVERFIRED OR UNDERBURNED BRICKS (LONDON STOCK QUALITY WAS VARIABLE). TREATMENT: REMOVE SPALLED BRICKWORK AND REPLACE WITH MATCHING SECOND-HAND LONDON STOCK (SALVAGE YARDS SUCH AS BROOKFIELD SALVAGE, LASSCO, OR LONDON BRICK COMPANY SECONDS SUPPLY MATCHING MATERIAL). NEW HANDMADE BRICK TO MATCH: MICHELMERSH LONDON BRICK RANGE (SLOUGH BLEND, REGATTA BLEND) MOST CLOSELY MATCHES ORIGINAL LONDON STOCK. (2) EFFLORESCENCE — WHITE CRYSTALLINE SALT DEPOSITS ON THE BRICK FACE, CAUSED BY WATER-SOLUBLE SALTS IN THE BRICK CLAY BEING DRAWN TO THE SURFACE AS MOISTURE MIGRATES AND EVAPORATES. NOT STRUCTURALLY DAMAGING; USUALLY RESOLVES NATURALLY ONCE THE MOISTURE SOURCE IS CONTROLLED. TREATMENT: DRY BRUSHING ONLY (NO ACID WASHING — THIS SETS THE SALTS BACK INTO THE BRICK). (3) DIAGONAL CRACKING THROUGH BRICKWORK — INDICATES DIFFERENTIAL MOVEMENT BETWEEN PARTS OF THE STRUCTURE. STAIR-STEP CRACKING THROUGH MORTAR JOINTS IS TYPICALLY DUE TO SUBSIDENCE (LONDON CLAY SHRINKAGE IN DROUGHT PERIODS), THERMAL MOVEMENT, OR SETTLEMENT. STRAIGHT VERTICAL OR HORIZONTAL CRACKING THROUGH BRICKS SUGGESTS MORE SIGNIFICANT STRUCTURAL LOADING. STRUCTURAL ENGINEER ASSESSMENT IS REQUIRED FOR ALL BUT MINOR SURFACE CRACKING.

CORRECT REPOINTING IN LIME MORTAR IS A SKILLED PROCESS THAT CANNOT BE RUSHED. THE STEPS ARE: (1) RAKING OUT — MINIMUM 15-20MM DEPTH OF EXISTING MORTAR MUST BE REMOVED BEFORE NEW MORTAR CAN BE APPLIED. FOR CEMENT MORTAR REPOINTING (WHICH MUST BE FULLY REMOVED): USE AN ANGLE GRINDER WITH MORTAR RAKE DISC (CAUTION: RISK OF DAMAGE TO BRICK FACE — SKILLED OPERATIVES ONLY) OR HAND TOOLS (PLUGGING CHISEL AND CLUB HAMMER — SLOWER BUT SAFER). NEVER USE AN ANGLE GRINDER WITH A CUTTING DISC ON LONDON STOCK BRICK — THE BRICK FACE IS ALMOST ALWAYS DAMAGED. COMPRESSED-AIR CHISEL TOOLS GIVE GOOD RESULTS FOR LARGE AREAS WITH SKILLED OPERATORS. (2) CLEANING AND PREPARATION — ALL LOOSE MATERIAL, DUST, AND DEBRIS MUST BE REMOVED FROM RAKED JOINTS BY AIR BLAST AND DAMPING DOWN WITH CLEAN WATER. JOINTS MUST BE PRE-WETTED TO PREVENT RAPID MOISTURE ABSORPTION FROM THE NEW MORTAR BY THE DRY BRICKWORK (WHICH WOULD CAUSE EARLY DRYING AND CRACKING OF THE NEW MORTAR). (3) MORTAR APPLICATION — TROWEL MORTAR FIRMLY INTO THE JOINT IN 3-4 PASSES FOR DEEP JOINTS; DO NOT APPLY IN ONE THICK LAYER AS THIS SLOWS CARBONATION AND CAUSES CRACKING. (4) CURING — NATURAL HYDRAULIC LIME MORTAR MUST BE KEPT SLOWLY DAMP (NOT WET) FOR MINIMUM 72 HOURS AFTER APPLICATION. IN HOT SUNNY CONDITIONS: HESSIAN OVER THE WORK AND MIST DAMPING TWICE A DAY. IN COLD CONDITIONS: NHL MORTAR MUST NOT BE APPLIED WHEN TEMPERATURES ARE BELOW 5°C (FROST KILLS HYDRAULIC LIME SET). (5) POINTING COLOUR MATCHING — FOR CONSERVATION AREA AND LISTED BUILDING PROPERTIES, COLOUR MATCHING THE EXISTING MORTAR IS OFTEN REQUIRED BY THE LPA. SAMPLES SHOULD BE SUBMITTED FOR APPROVAL BEFORE LARGE-SCALE WORKS PROCEED.

BRICK CLEANING IS SOMETIMES NEEDED AFTER CONSTRUCTION (TO REMOVE MORTAR SMEARS) OR IN CONSERVATION CONTEXTS (TO REMOVE PAINT, BLACK CARBON DEPOSITS, OR CEMENT RENDER). KEY PRINCIPLES: THE LEAST AGGRESSIVE METHOD THAT ACHIEVES THE DESIRED RESULT IS ALWAYS CORRECT — EXCESSIVE CLEANING DAMAGES THE BRICK FACE AND REDUCES ITS DURABILITY. APPROVED METHODS FOR LONDON STOCK BRICK: (1) LOW-PRESSURE WATER WASH (MAX 100 PSI, WIDE FAN NOZZLE) — FOR GENERAL SOILING; SAFE FOR ALL BRICK TYPES. (2) LATEX PAINT POULTICE (PEELABLE COATING APPLIED, ALLOWED TO DRY, PEELED OFF WITH PAINT) — FOR PAINT REMOVAL WITHOUT ACID. (3) DILUTE HYDROCHLORIC ACID (5-10% SOLUTION) — FOR NEW CONSTRUCTION MORTAR SMEAR REMOVAL ONLY. MUST BE THOROUGHLY RINSED. NEVER USE ON OLD BRICKWORK WITH LIME MORTAR — THE ACID WILL ATTACK THE LIME. (4) DOFF CLEANING (SUPERHEATED STEAM, 150°C) — GENTLE, EFFECTIVE FOR BLACK SOOTY DEPOSITS AND BIOGROWTH. NO CHEMICALS REQUIRED. SUITABLE FOR CONSERVATION AREA AND LISTED BUILDING FACADES. (5) TORC CLEANING (VORTEX OF FINE PARTICLES + WATER) — HERITAGE-APPROVED LOW-PRESSURE SYSTEM FOR STUBBORN DEPOSITS. NEVER USE: HIGH-PRESSURE SAND OR GRIT BLASTING (DESTROYS THE FIRE SKIN ON OLD BRICK, CAUSING RAPID DETERIORATION); MURIATIC ACID (HYDROCHLORIC ACID ABOVE 10%) ON OLD BRICKWORK OR LIME MORTAR.

LONDON MARKET RATES FOR BRICKWORK AND POINTING WORKS (EXPERIENCED TRADESPEOPLE, 2025): LIME REPOINTING — STANDARD ELEVATION (LONDON STOCK, NHL 3.5 MORTAR, SCAFFOLD INCLUDED): £60-£120 PER M2. INTERNAL BRICKWORK REPOINTING (NO SCAFFOLD): £45-£80 PER M2. CEMENT-TO-LIME REPOINTING (INCLUDING FULL RAKE-OUT OF CEMENT POINTING): £80-£140 PER M2 (THE RAKE-OUT IS THE MOST LABOUR-INTENSIVE PART). BRICK REPLACEMENT (ISOLATED SPALLED BRICKS): £30-£80 PER BRICK INCLUDING SUPPLY AND FIT. FULL FRONT ELEVATION REPOINTING (STANDARD 3-STOREY LONDON TERRACE, 60M2): £4,500-£8,000 INCLUDING SCAFFOLD. CHIMNEY STACK REPOINT AND REFLASH (INCLUDING SCAFFOLD AND LEAD FLASHING REPLACEMENT): £1,200-£2,500. EFFLORESCENCE TREATMENT AND FACADE CLEAN: £400-£900 FOR STANDARD TERRACE FRONT. BRICK CLEANING (DOFF OR TORC, STANDARD TERRACE FRONT ELEVATION): £600-£1,500. STRUCTURAL CRACK REPAIR (INJECT GROUT + STAINLESS STEEL HELIFIX HELICAL TIES + REPOINT): £800-£2,500 DEPENDING ON EXTENT. NOTE: SCAFFOLD ACCESS IS REQUIRED FOR ALL ABOVE-GROUND-FLOOR ELEVATION WORKS AND ADDS £800-£2,000 FOR A STANDARD 3-STOREY TERRACE DEPENDING ON DURATION AND ACCESS CONSTRAINTS. IN LONDON, MANY TERRACES REQUIRE PAVEMENT LICENCES FROM THE LONDON BOROUGH FOR SCAFFOLD FOOTPRINT ON THE PUBLIC HIGHWAY — ALLOW 2-4 WEEKS FOR LICENCE PROCESSING.