Damp Proofing London: Identifying Types, Treatments & Costs

UNDERSTANDING WHICH TYPE OF DAMP AFFECTS YOUR LONDON PROPERTY IS THE SINGLE MOST IMPORTANT STEP BEFORE SPENDING A PENNY ON TREATMENT. THE THREE TYPES ARE FUNDAMENTALLY DIFFERENT IN CAUSE, PATTERN, AND CURE:

TYPE 1 — RISING DAMP: MOISTURE FROM THE GROUND RISING THROUGH THE CAPILLARY PORES OF MASONRY WALLS. TRUE RISING DAMP PRODUCES A CHARACTERISTIC HIGH TIDE MARK 0.5-1.0M ABOVE FLOOR LEVEL, WITH SALT DEPOSITS (HYGROSCOPIC SALTS DEPOSITED AS WATER EVAPORATES), TIDE MARK STAINING, AND WALLPAPER PEELING FROM THE BOTTOM UP. THE PATTERN IS TYPICALLY HORIZONTAL ACROSS THE LOWER SECTION OF THE WALL, NOT AROUND SPECIFIC OPENINGS. IT IS CAUSED BY AN ABSENT, FAILED, OR BRIDGED DAMP PROOF COURSE (DPC).

TYPE 2 — PENETRATING DAMP: WATER ENTERING THROUGH A SPECIFIC DEFECT IN THE BUILDING ENVELOPE — A LEAKING GUTTER, CRACKED RENDER, FAILED FLASHINGS, POROUS BRICKWORK, DEFECTIVE POINTING, OR AROUND WINDOW FRAMES. PENETRATING DAMP IS TYPICALLY LOCALISED TO A SPECIFIC AREA AND IS WORSE AFTER HEAVY RAIN. IT OFTEN APPEARS AS A WET PATCH ON AN INTERNAL WALL OR CEILING THAT DRIES OUT BETWEEN RAIN EVENTS. IN FLAT ROOFS AND PARAPET WALLS, PENETRATING DAMP IS A COMMON AND OFTEN DRAMATIC CAUSE OF INTERNAL WATER DAMAGE.

TYPE 3 — CONDENSATION: THE MOST COMMON FORM OF DAMP IN UK RESIDENTIAL PROPERTIES. WARM MOIST AIR (FROM COOKING, BATHING, BREATHING, AND DRYING CLOTHES) CONTACTS A COLD SURFACE AND THE MOISTURE CONDENSES. TYPICALLY APPEARS AS BLACK MOULD GROWTH (CLADOSPORIUM, ASPERGILLUS, STACHYBOTRYS SPECIES) ON COLD SURFACES — EXTERNAL WALLS, WINDOW REVEALS, BEHIND FURNITURE, IN CORNERS. CONDENSATION IS FUNDAMENTALLY A VENTILATION AND HEATING PROBLEM, NOT A STRUCTURAL DAMP PROBLEM.

CRITICAL POINT: A METRE READING (THE CLASSIC DPC SALESPERSON TOOL) CANNOT DISTINGUISH BETWEEN THESE THREE TYPES. HIGH ELECTRICAL READINGS IN A WALL MAY INDICATE ANY OF THE THREE TYPES — OR HYGROSCOPIC SALTS ABSORBING ATMOSPHERIC MOISTURE (WHICH GIVES HIGH READINGS EVEN IN COMPLETELY DRY MASONRY). PROPER DIAGNOSIS REQUIRES VISUAL ASSESSMENT, CARBIDE BOMB TEST, SALT ANALYSIS, AND AN UNDERSTANDING OF THE BUILDING'S PHYSICS.

WHERE RISING DAMP IS CONFIRMED BY PROPER INVESTIGATION (PHYSICAL DPC IS ABSENT OR BRIDGED, TIDE MARK PATTERN IS CONSISTENT, SALT ANALYSIS CONFIRMS HYGROSCOPIC SALTS), THE FOLLOWING TREATMENTS ARE APPROPRIATE:

1. CHEMICAL INJECTION DPC: THE MOST WIDELY USED TREATMENT FOR RISING DAMP IN LONDON. A CONTINUOUS LINE OF HOLES (10-12MM DIAMETER) IS DRILLED AT 120MM CENTRES ALONG THE MORTAR BED JOINT AT APPROXIMATELY 150MM ABOVE EXTERNAL GROUND LEVEL. DAMP-PROOFING CREAM OR FLUID IS INJECTED INTO EACH HOLE AND ALLOWED TO CURE, FORMING AN IMPREGNATED ZONE OF WATER-REPELLENT MATERIAL (SILANE OR SILICONE OLIGOMER). AFTER CURING (TYPICALLY 24-48 HOURS), HOLES ARE REPOINTED. SPECIFIED PRODUCTS: SAFEGUARD DRYZONE DAMP-PROOFING CREAM (500ML CARTRIDGES, 10MM HOLES AT 120MM CENTRES, SYRINGE INJECTION); TRITON TF300 SYSTEM; PERMAGARD DRYROD DIFFUSION TUBES (PASSIVE DIFFUSION SYSTEM — SLOWER BUT SIMPLER). COST: £600-£1,500 FOR A STANDARD TERRACE (20-30 METRES OF DPC INJECTION) SUPPLY AND INSTALL. NOTE: THE INJECTION ALONE DOES NOT REMOVE EXISTING SALT CONTAMINATION — INTERNAL RE-PLASTERING WITH SALT-RESISTANT (TANKING) PLASTER IS REQUIRED.

2. INTERNAL TANKING: WHERE RISING DAMP IS SEVERE AND EXTERNAL EXCAVATION IS NOT PRACTICAL, INTERNAL WATERPROOFING (TANKING) COMBINED WITH AN INTERNAL DPC IS AN ALTERNATIVE. INVOLVES HACKING OFF CONTAMINATED PLASTER TO THE FULL HEIGHT OF DAMP DAMAGE, APPLYING A CEMENT-BASED TANKING SLURRY (SIKA WATERTIGHT CONCRETE SYSTEM: SIKA-1 WATERPROOF ADMIXTURE + SIKA WATERBAR B) OR BITUMEN TANKING (REMMERS MB2K), AND REPLASTERING WITH RENOVATION PLASTER (KNAUF AQUAPANEL RENDER, BAUMIT SANOVA).

3. EXTERNAL BARRIER (EXCAVATION AND MEMBRANE): EXCAVATING EXTERNALLY DOWN TO THE FOUNDATION LEVEL AND APPLYING A WATERPROOF MEMBRANE OR TANKING SYSTEM ON THE EXTERNAL FACE OF THE WALL. THE MOST EFFECTIVE METHOD BUT EXPENSIVE AND DISRUPTIVE. TYPICALLY ONLY WARRANTED FOR SEVERE BASEMENT AND LOWER-GROUND-FLOOR SCENARIOS.

IMPORTANT CAVEAT: THE PROPERTY CARE ASSOCIATION (PCA) AND BRE (BUILDING RESEARCH ESTABLISHMENT) RESEARCH INDICATE THAT RISING DAMP IS FREQUENTLY OVER-DIAGNOSED BY DAMP COMPANIES WITH A COMMERCIAL INTEREST IN SELLING EXPENSIVE TREATMENTS. ALWAYS OBTAIN AN INDEPENDENT STRUCTURAL SURVEY (RICS) ALONGSIDE A DAMP COMPANY REPORT BEFORE COMMISSIONING TREATMENT.

PENETRATING DAMP REQUIRES FINDING AND ELIMINATING THE MOISTURE SOURCE — NOT TREATING THE INTERNAL SYMPTOM. TREATING THE SYMPTOM WITHOUT FIXING THE SOURCE SIMPLY MEANS THE PROBLEM RETURNS. COMMON SOURCES IN LONDON PROPERTIES:

ROOFS AND GUTTERS: — BLOCKED OR LEAKING CAST IRON OR UPVC GUTTERING: CHECK JOINTS, BRACKETS, AND OUTLETS. REPLACE SEALS (PUSH-FIT RUBBER GASKETS) OR REPLACE SECTIONS. CAST IRON GUTTERS ON VICTORIAN PROPERTIES: REPAINT EXTERNALLY WITH HAMMERITE OR BEDLAM METAL PAINT AFTER DERUSTING. — CRACKED CHIMNEY STACK FLASHING: LEAD SOAKERS AND STEPPED FLASHING ON CHIMNEY HAUNCHES ARE A COMMON PENETRATING DAMP SOURCE IN LONDON TERRACES. REPLACE FAILED LEAD WITH NEW CODE 4 LEAD (2.5MM THICKNESS). — FLAT ROOF PONDING: FAILED FELT, CRACKED GRP, OR OPEN SEAMS IN FLAT ROOFING ALLOW DIRECT WATER INGRESS. REROOFING WITH SARNAFIL G410-15EL (SINGLE-PLY PVC MEMBRANE) IS THE DURABLE SOLUTION.

WALLS: — FAILED POINTING: CEMENT MORTAR POINTING ON LONDON STOCK BRICK CRACKS AND SHRINKS, CREATING OPEN JOINTS THROUGH WHICH RAIN DRIVES. REPOINT WITH NHL 3.5 LIME MORTAR ON ALL SOLID BRICK PERIOD PROPERTIES. — CRACKED RENDER: HAIRLINE CRACKS IN CEMENT RENDER ALLOW CAPILLARY WATER INGRESS. FILL WITH FLEXIBLE SEALANT (GEOCEL 2000 SILICONE, SOUDAL FIX ALL) FOR ISOLATED CRACKS; HACK OFF AND REREND FOR EXTENSIVE CRACKING. — POROUS BRICKWORK: LONDON STOCK BRICK IS GENERALLY ROBUST BUT VERY POROUS. STORMDRY MASONRY CREAM (SAFEGUARD EUROPE) APPLIED TO CLEAN MASONRY REDUCES WATER ABSORPTION BY UP TO 95% WITHOUT ALTERING BREATHABILITY OR APPEARANCE. A 5-LITRE TUB COVERS ~25M2. APPLICATION REQUIRES TWO COATS. SERVICE LIFE 10-20 YEARS.

WINDOWS AND DOORS: — FAILED SILICON SEALANT AT WINDOW FRAMES: RAKE OUT OLD FAILED SEALANT AND REAPPLY WITH BOND IT ULTRA PRO SILICONE OR SOUDAL FIX ALL WEATHER SHIELD. — DEFECTIVE WINDOW CILLS: CRACKED STONE, CONCRETE, OR RENDER CILLS LET WATER INTO THE JOINT BETWEEN CILL AND WALL. REPAIR CILLS AND APPLY FLEXIBLE SEALANT. — NO DRIP GROOVE ON WINDOWSILLS: OLDER TIMBER SILLS WITHOUT A DRIP GROOVE ALLOW WATER TO RUN BACK AGAINST THE WALL. ROUT A NEW DRIP GROOVE 12-15MM FROM THE FRONT EDGE.

CONDENSATION IS BY FAR THE MOST COMMON FORM OF DAMP AFFECTING LONDON RESIDENTIAL PROPERTIES, YET IT IS ROUTINELY MISDIAGNOSED AS RISING DAMP OR PENETRATING DAMP. THE CAUSE IS ALWAYS THE SAME: WARM, MOISTURE-LADEN AIR MEETING A COLD SURFACE BELOW THE DEW POINT.

RISK FACTORS IN LONDON HOMES: — SOLID WALLS (LOW THERMAL MASS BUT HIGH COLD SURFACE RISK IN WINTER) — LACK OF WHOLE-HOUSE MECHANICAL VENTILATION — INADEQUATE WINDOW VENTILATION (REPLACEMENT DG UNITS WITHOUT TRICKLE VENTS) — DRYING CLOTHES INDOORS (GENERATES 2-3 LITRES OF MOISTURE PER LOAD) — COOKING WITHOUT EXTRACTION VENTILATION — OVERCROWDING OR HIGH OCCUPANCY

TREATMENT — THE CORRECT APPROACH: 1. VENTILATION: THE FUNDAMENTAL CURE FOR CONDENSATION. OPTIONS: — POSITIVE INPUT VENTILATION (PIV) UNIT: NUAIRE DRIMASTER ECO (LOFT-MOUNTED, DILUTES INTERNAL MOISTURE WITH FILTERED EXTERNAL AIR, ~0.5-2.0 ACH). COSTS £350-£600 SUPPLY AND INSTALL. MOST COST-EFFECTIVE FIRST STEP FOR CONDENSATION IN LONDON TERRACES. — HEAT RECOVERY VENTILATION (MVHR): ZEHNDER COMFOAIR Q350, VENT-AXIA SENTINEL KINETIC PLUS. PROVIDES 93% HEAT RECOVERY, WHOLE-HOUSE FILTERED VENTILATION. COSTS £3,000-£6,000 INSTALLED. RECOMMENDED FOR NEW EXTENSIONS AND WHOLE-HOUSE RENOVATIONS. — BATHROOM AND KITCHEN MECHANICAL EXTRACT: MANROSE MF100T (TIMER-CONTROLLED); AIRFLOW ICON15 (HUMIDITY-CONTROLLED — DETECTS MOISTURE AND RUNS UNTIL HUMIDITY DROPS). MINIMUM 15L/S FOR BATHROOMS, 30L/S FOR OPEN-PLAN KITCHEN-DINERS. 2. HEATING: MAINTAINING A MINIMUM BACKGROUND TEMPERATURE OF 15-18°C THROUGHOUT THE HOUSE PREVENTS COLD SURFACES DROPPING BELOW DEW POINT. SMART THERMOSTATIC SYSTEMS (TADO, HEATMISER) HELP MAINTAIN CONSISTENT BACKGROUND HEAT. 3. MOULD TREATMENT: EXISTING MOULD MUST BE TREATED BEFORE REDECORATING. CLEAN WITH ANTI-MOULD SOLUTION (POLY CELL MOULD KILLER OR BLEACH SOLUTION 1:4 DILUTION), ALLOW TO DRY, APPLY ANTI-MOULD PAINT (RONSEAL ANTI-MOULD PAINT, DULUX WEATHERSHIELD ANTI-MOULD). DO NOT PAINT OVER ACTIVE MOULD — IT WILL REGROW WITHIN WEEKS.

DAMP TREATMENT COSTS VARY ENORMOUSLY DEPENDING ON THE CORRECT DIAGNOSIS:

CONDENSATION TREATMENT (POSITIVE INPUT VENTILATION): NUIRE DRIMASTER ECO UNIT + INSTALLATION: £350-£600. NO REPLASTERING REQUIRED. MOULD CLEAN + ANTI-MOULD PAINT: £200-£500. TOTAL: £550-£1,100.

PENETRATING DAMP (SOURCE REPAIR — TYPICAL SCENARIOS): GUTTER REPAIR AND RESEALING: £150-£400 FLASHING REPLACEMENT (LEAD CHIMNEY): £500-£1,500 Repointing (20M RUN, NHL 3.5): £800-£2,000 STORMDRY CREAM APPLICATION (80M2 WALL): £600-£1,200 FLAT ROOF REPLACEMENT (25M2 SARNAFIL): £2,500-£5,000

RISING DAMP TREATMENT (CONFIRMED CASE): CHEMICAL DPC INJECTION (20M RUN): £600-£1,200 HACKING OFF AND RENOVATION REPLASTER (20M2): £1,000-£2,500 SALT-RESISTANT BASEBOARD (PERMAGARD SALT PRO): INCLUDED IN REPLASTER TOTAL RISING DAMP TREATMENT: £1,600-£3,700

FINDING A REPUTABLE CONTRACTOR: — PROPERTY CARE ASSOCIATION (PCA) MEMBERS MUST ADHERE TO A CODE OF PRACTICE AND TECHNICALLY COMPETENT PERSON STANDARD. PREFER PCA MEMBERS FOR DAMP INVESTIGATIONS AND TREATMENT. — RICS BUILDING SURVEYORS CAN PROVIDE INDEPENDENT DAMP INVESTIGATIONS NOT TIED TO A COMMERCIAL TREATMENT OUTCOME. — BE CAUTIOUS OF FREE DAMP SURVEYS OFFERED BY DPC COMPANIES — THESE ARE SALES VISITS, NOT INDEPENDENT SURVEYS. THE DIAGNOSIS WILL ALMOST ALWAYS RECOMMEND THE COMPANY'S PRODUCTS.