Mould and Damp in London Homes: Causes, Diagnosis, and Treatment

RISING DAMP IS THE UPWARD MOVEMENT OF GROUND MOISTURE THROUGH THE CAPILLARY STRUCTURE OF A MASONRY WALL — DRIVEN BY CAPILLARY SUCTION IN THE PORES OF THE BRICK AND MORTAR. IT IS A REAL PHENOMENON, BUT SIGNIFICANTLY LESS COMMON THAN CONDENSATION DAMP — AND FREQUENTLY MISDIAGNOSED.

DIAGNOSTIC INDICATORS OF GENUINE RISING DAMP: TIDE MARK PATTERN AT 900MM TO 1200MM HEIGHT ON GROUND-FLOOR INTERNAL WALLS — RISING DAMP TYPICALLY REACHES A MAXIMUM HEIGHT OF APPROXIMATELY 1.0 TO 1.2 METRES (ABOVE THIS HEIGHT, EVAPORATION EXCEEDS CAPILLARY RISE). SALTS CRYSTALLISING ON THE WALL SURFACE (EFFLORESCENCE) — GROUND MOISTURE CARRIES DISSOLVED SALTS WHICH CRYSTALLISE AS THE WATER EVAPORATES AT THE WALL SURFACE. THESE ARE HYGROSCOPIC SALTS (PARTICULARLY NITRATES AND CHLORIDES FROM GROUND CONTAMINATION) THAT ABSORB MOISTURE FROM THE AIR — THEY REMAIN DAMP EVEN AFTER THE RISING DAMP IS TREATED. CONSISTENT DAMP PATTERN EVEN IN SUMMER — CONDENSATION DAMP IS SEASONAL (WORSE IN WINTER); RISING DAMP IS RELATIVELY CONSISTENT YEAR-ROUND. DAMP METER READINGS ELEVATED IN THE WALL MATERIAL (NOT JUST ON THE SURFACE) — USING A CARBIDE BOMB TEST (NOT JUST A SURFACE RESISTANCE METER) TO CONFIRM MOISTURE IN THE WALL BODY.

CHEMICAL DPC INJECTION (THE STANDARD TREATMENT FOR GENUINE RISING DAMP): WHERE RISING DAMP IS CONFIRMED, A CHEMICAL DPC (DAMP-PROOF COURSE) IS THE APPROPRIATE TREATMENT. PRODUCTS: DRYZONE DPC INJECTION CREAM (BY SAFEGUARD EUROPE) IS THE LEADING UK DPC INJECTION CREAM — APPLIED INTO DRILLED HOLES AT 120MM DEPTH CENTRES AT COURSE HEIGHT IN THE MORTAR JOINT APPROXIMATELY 150MM ABOVE GROUND LEVEL. THE DRYZONE CREAM DIFFUSES INTO THE MASONRY AND CREATES A WATER-REPELLENT SILANE ZONE THAT BREAKS THE CAPILLARY PATH. REMMERS KIESOL C (LIQUID SILANE INJECTION) — AN ALTERNATIVE LIQUID INJECTION DAMP-PROOF TREATMENT. REMEDIAL PLASTERING: AFTER DPC INJECTION, THE ORIGINAL PLASTER MUST BE REMOVED TO A HEIGHT OF 300MM ABOVE THE DPC TREATMENT ZONE AND REPLACED WITH REMMERS SANIERPUTZ (RENOVATION PLASTER — POROUS, ALLOWS RESIDUAL MOISTURE TO EVAPORATE THROUGH THE PLASTER WITHOUT STAINING THE SURFACE) OR SIMILAR.

CONDENSATION IS BY FAR THE MOST COMMON FORM OF DAMP IN LONDON RESIDENTIAL PROPERTIES — YET IT IS ROUTINELY MISDIAGNOSED AS RISING DAMP OR PENETRATING DAMP, LEADING TO UNNECESSARY AND EXPENSIVE REMEDIATION.

WHAT CAUSES CONDENSATION DAMP IN LONDON HOMES: CONDENSATION OCCURS WHEN WARM MOIST AIR (FROM COOKING, BATHING, RESPIRATION, DRYING CLOTHES INDOORS — ALL COMMON IN OCCUPIED LONDON HOMES) COMES INTO CONTACT WITH A COLD SURFACE AND COOLS BELOW ITS DEW POINT — THE WATER VAPOUR IN THE AIR CONDENSES TO LIQUID. IN LONDON VICTORIAN TERRACES, THE COLD SURFACES THAT TRIGGER CONDENSATION ARE TYPICALLY: EXTERNAL WALLS (POORLY INSULATED SOLID BRICK WALLS THAT HAVE A COLD INNER SURFACE IN WINTER — THERMAL MASS ABSORBS COLD). COLD NORTH-FACING EXTERNAL WALLS. THERMAL BRIDGES IN THE BUILDING FABRIC (JUNCTIONS BETWEEN FLOOR SLABS AND WALLS, LINTELS, TIE BEAMS — COLD SPOTS WHERE CONDENSATION PREFERENTIALLY OCCURS).

CLASSIC SIGNS OF CONDENSATION DAMP IN LONDON HOMES: MOULD GROWTH ON INTERIOR WALLS AND CEILINGS — PARTICULARLY ASPERGILLUS NIGER (BLACK MOULD) AND CLADOSPORIUM (GREEN/BLACK MOULD). MOULD IS MOST COMMON AT WALL/CEILING JUNCTIONS, IN CORNERS, BEHIND FURNITURE PLACED AGAINST EXTERNAL WALLS (REDUCED AIR CIRCULATION), AND ON COLD NORTH-FACING WALLS. CONDENSATION ON WINDOWS (WATER BEADING ON THE INSIDE OF WINDOW GLASS) — A CLEAR INDICATOR THAT INDOOR HUMIDITY IS ELEVATED. MUSTY SMELL FROM BUILDING MATERIALS AFFECTED BY MOULD. SEASONAL PATTERN — WORSE IN WINTER (WHEN EXTERNAL TEMPERATURES ARE LOWER, SURFACES ARE COLDER, AND HEATING INCREASES WARM MOIST AIR CIRCULATION IN A CLOSED BUILDING).

CORRECT TREATMENT FOR CONDENSATION DAMP: THE FUNDAMENTAL TREATMENTS FOR CONDENSATION ARE: REDUCE INDOOR HUMIDITY (INCREASED MECHANICAL VENTILATION, EXTRACTOR FANS IN BATHROOMS AND KITCHENS, BACKGROUND TRICKLE VENTS IN WINDOWS, POSITIVE INPUT VENTILATION UNITS). IMPROVE THERMAL PERFORMANCE OF COLD SURFACES (INTERNAL WALL INSULATION — GYPROC THERMALINE PLUS BACKED PLASTERBOARD OR KINGSPAN KOOLTHERM K17 FOIL-FACED PIR BOARD ON MECHANICAL FIX OR DOT AND DAB — ELIMINATES THE COLD INTERNAL WALL SURFACE). INSTALL MOULD-RESISTANT DECORATION (DULUX ANTI-MOULD PAINT, RONSEAL ANTI-MOULD PAINT) AS A SECONDARY MEASURE.

PENETRATING DAMP OCCURS WHERE WATER ENTERS THE BUILDING FABRIC FROM THE OUTSIDE THROUGH DEFECTS IN THE EXTERNAL ENVELOPE — NOT FROM THE GROUND (RISING) OR FROM INTERNAL MOISTURE (CONDENSATION).

COMMON SOURCES OF PENETRATING DAMP IN LONDON VICTORIAN TERRACES: FAILED POINTING OR MORTAR JOINTS: THE MOST COMMON CAUSE OF PENETRATING DAMP IN LONDON PERIOD PROPERTIES. ORIGINAL VICTORIAN LIME MORTAR JOINTS DETERIORATE OVER TIME AND ALLOW WATER ENTRY. FAILED EXTERNAL WINDOW SILLS AND SILL/WALL JUNCTIONS: CRACKED STONE SILLS, FAILED SILICONE JOINT BETWEEN WINDOW FRAME AND BRICKWORK, MISSING OR FAILED SILL DRIP EDGE. CHIMNEY STACKS AND LEAD FLASHINGS: FAILED LEAD FLASHINGS AT THE CHIMNEY STACK/ROOF JUNCTION ARE A VERY COMMON SOURCE OF WATER INGRESS IN LONDON VICTORIAN TERRACES — WATER FOLLOWS THE MASONRY DOWN THROUGH THE CHIMNEY BREAST AND APPEARS AS A DAMP PATCH ON INTERNAL WALLS NEAR THE FIREPLACE OR ON THE CEILING AT FIRST-FLOOR LEVEL. BLOCKED OR LEAKING GUTTERS: OVERFLOWING GUTTERS SOAK THE FACE OF THE WALL BELOW — SATURATING THE BRICKWORK AND CAUSING PERSISTENT WET PATCHES ON INTERNAL WALLS AT HIGH LEVEL. CRACKED RENDER OR FAILED POINTING ON PARAPET WALLS: PARAPETS ON FLAT-ROOF EXTENSIONS ARE A COMMON SOURCE OF WATER ENTRY.

TREATMENT FOR PENETRATING DAMP: THE TREATMENT IS ALWAYS TO IDENTIFY AND RECTIFY THE SOURCE OF WATER ENTRY — NOT TO APPLY A BLANKET WATERPROOF COATING TO THE WALL. IDENTIFY THE SOURCE: VISUAL INSPECTION FROM SCAFFOLD; WATER TESTING BY HOSE TO ISOLATE THE ENTRY POINT. REPAIR THE DEFECT: REPOINT WITH NHL LIME MORTAR; REPLACE FAILED LEAD FLASHING; CLEAR AND REPAIR GUTTERS; REPLACE SILL; RE-SEAL WINDOW FRAME TO BRICKWORK WITH SOUDAL SILICONE OR ARBOSIL 1081. ALLOW WALL TO DRY: PENETRATING DAMP WALLS MAY TAKE 3 TO 12 MONTHS TO FULLY DRY AFTER THE SOURCE IS REMEDIATED — REPLASTERING OR DECORATION TOO EARLY WILL RESULT IN FAILURE.

MOULD IN LONDON HOMES (PREDOMINANTLY ASPERGILLUS NIGER — BLACK MOULD — AND CLADOSPORIUM) IS A HEALTH CONCERN AS WELL AS A BUILDING PATHOLOGY PROBLEM — PROLONGED EXPOSURE TO BLACK MOULD SPORES HAS BEEN ASSOCIATED WITH RESPIRATORY PROBLEMS, ALLERGIC REACTIONS, AND EXACERBATION OF ASTHMA.

SAFE MOULD REMOVAL: SMALL PATCHES OF MOULD (UNDER 1 M²) CAN BE SAFELY CLEANED BY A COMPETENT HOMEOWNER USING: PPE: N95 DUST MASK, DISPOSABLE GLOVES, EYE PROTECTION. CLEANING AGENT: BLEACH SOLUTION (1 PART HOUSEHOLD BLEACH TO 9 PARTS WATER — EFFECTIVE ON NON-POROUS SURFACES); RONSEAL MOULD KILLER SOLUTION; OR ZINSSER MOULD KILLER CONCENTRATE. APPLY CLEANING AGENT, LEAVE FOR 10 MINUTES, SCRUB AND RINSE. SEAL WITH ZINSSER BULLS EYE 1-2-3 PRIMER (WATER-BASED STAIN BLOCKER — SEALS RESIDUAL MOULD STAINING AND INHIBITS RE-GROWTH) BEFORE DECORATING.

LARGE PATCHES OF MOULD (OVER 1 M² OR WHERE PENETRATING BELOW PLASTER): PROFESSIONAL REMEDIATION IS RECOMMENDED — MOULD COLONIES THAT HAVE PENETRATED INTO PLASTER, PLASTERBOARD, OR TIMBER FRAMING CANNOT BE EFFECTIVELY CLEANED AT SURFACE LEVEL. THE AFFECTED MATERIAL MUST BE REMOVED AND DISPOSED OF IN SEALED BAGS, AND THE SUBSTRATE TREATED WITH SPECIALIST FUNGICIDE BEFORE REPLASTERING.

MOULD-RESISTANT REDECORATION: AFTER MOULD TREATMENT, DECORATE WITH DULUX TRADE ENDURANCE+ (ANTI-MOULD ADDITIVE — 5-YEAR MOULD RESISTANCE CLAIM), JOHNSTONE'S COVAPLUS VINYL MATT WITH MOULD INHIBITOR, OR RONSEAL ANTI-MOULD WALL COATING. IN BATHROOMS AND KITCHENS, TILE WHERE POSSIBLE RATHER THAN PAINTING — TILES ARE EASIER TO CLEAN AND DO NOT SUPPORT MOULD GROWTH.

THE CORRECT DIAGNOSIS OF DAMP IN A LONDON PROPERTY REQUIRES METHODICAL INVESTIGATION — NOT SIMPLY ACCEPTING THE FIRST DIAGNOSIS OFFERED BY A TRADESPERSON WHO MAY HAVE A COMMERCIAL INTEREST IN A PARTICULAR TREATMENT.

DIAGNOSTIC TOOLKIT: SURFACE RESISTANCE METER (DAMP METER): WIDELY USED BUT LIMITED — MEASURES ELECTRICAL RESISTANCE AT THE WALL SURFACE; MISLED BY SURFACE SALTS AND SURFACE CONDENSATION. A HIGH SURFACE READING DOES NOT CONFIRM RISING DAMP. CARBIDE BOMB TEST (SPEEDY MOISTURE TEST): REMOVES A CORE SAMPLE OF WALL MATERIAL, GRINDS IT, AND MEASURES MOISTURE CONTENT BY REACTING WITH CALCIUM CARBIDE — THE MOST RELIABLE IN-SITU MOISTURE TEST FOR WALL MATERIALS. BORESCOPE CAMERA: VISUAL INSPECTION OF WALL CAVITIES, ROOF SPACES, AND HIDDEN AREAS TO IDENTIFY DEFECTS. THERMAL IMAGING: IDENTIFIES COLD SPOTS AND THERMAL BRIDGING — COLD BRIDGES THAT CAUSE CONDENSATION ARE IMMEDIATELY VISIBLE IN A THERMAL IMAGE (PARTICULARLY USEFUL IN LONDON VICTORIAN TERRACES WHERE BRICK TIES, LINTELS, AND FLOOR EDGE JUNCTIONS ARE COMMON COLD BRIDGES). SALT ANALYSIS: LABORATORY ANALYSIS OF A PLASTER SAMPLE TO IDENTIFY THE TYPES OF SALTS PRESENT — NITRATES AND CHLORIDES SUGGEST GROUND-WATER CONTAMINATION (RISING DAMP); ABSENCE OF GROUND-ORIGIN SALTS STRONGLY SUGGESTS CONDENSATION OR PENETRATING DAMP.

DAMP TREATMENT COSTS VARY WIDELY DEPENDING ON THE DAMP TYPE AND EXTENT.

CONDENSATION TREATMENT: MECHANICAL VENTILATION (NUAIRE CYFAN BATHROOM EXTRACTOR FAN INSTALLATION): £150 TO £350 SUPPLY AND INSTALL PER FAN. POSITIVE INPUT VENTILATION UNIT (NUAIRE DRIMASTER ECO — WHOLE-HOUSE PIV UNIT IN LOFT): £400 TO £800 SUPPLY AND INSTALL. INTERNAL WALL INSULATION (GYPROC THERMALINE PLUS 37.5MM DOT-AND-DAB — PER M² SUPPLY AND INSTALL): £35 TO £60 PER M². FOR A TYPICAL LONDON TERRACE EXTERNAL WALL (12 M²): £420 TO £720. MOULD TREATMENT AND REDECORATION (PER ROOM — PROFESSIONAL CLEAN, ZINSSER PRIMER, ANTI-MOULD PAINT): £400 TO £1,200.

RISING DAMP TREATMENT (GENUINE RISING DAMP — CONFIRMED BY CARBIDE TEST AND SALT ANALYSIS): CHEMICAL DPC INJECTION (DRYZONE CREAM — SUPPLY AND INSTALL, REPLASTER WITH REMMERS SANIERPUTZ, REDECORATE): £1,500 TO £4,000 FOR A TYPICAL LONDON TERRACE GROUND-FLOOR ROOM.

PENETRATING DAMP REMEDIATION: REPOINTING (PER M²): £25 TO £60. LEAD FLASHING REPLACEMENT (CHIMNEY STACK SOAKERS AND BACK GUTTER): £500 TO £1,500. GUTTER CLEARING AND REPAIR: £80 TO £300. ALLOW 3 TO 12 MONTHS DRY-OUT BEFORE REPLASTERING — REPLASTERING COST £300 TO £800 PER ROOM AFTER DRY-OUT.

INDEPENDENT DAMP SURVEY (RICS-QUALIFIED SURVEYOR — CORRECT DIAGNOSIS BEFORE COMMISSION OF WORKS): £300 TO £800. THIS INVESTMENT IN CORRECT DIAGNOSIS CAN SAVE THOUSANDS IN UNNECESSARY REMEDIATION.