07576 573615tom@cbsdamp.co.uk Mon–Fri 8am–8pm · Sat 8am–1pm · Sun closed About Services Areas Our work Contact 07576 573615Request Free Survey HomeServicesWaterproofing & tanking Damp proofing & remedial treatment specialists # Structural Waterproofing& Tanking in Harrow Below-ground rooms need a waterproofing system, not a coat of damp-seal paint. Membrane and cementitious tanking specified to suit the structure, installed as an approved Sovereign and Wykamol contractor, with a free survey and a fixed price. Request your free survey 07576 573615 Sovereign & Wykamol approved contractor · 10-year workmanship guarantee · 10-year QANW insurance-backed guarantee 10 years Workmanship guarantee on waterproofing 10 years QANW insurance-backed guarantee £0 Survey, diagnosis and fixed-price quotation £2m Public liability insurance held Service overview ## What structural waterproofing is, and when a cellar needs it Structural waterproofing, often called tanking, is the controlled management of water below ground level. Where a wall or floor is surrounded by soil, water arrives under hydrostatic pressure rather than as the occasional splash, so the solution is either a barrier strong enough to resist that pressure or a drained system that collects the water and takes it away. Two approaches cover most properties. A cementitious tanking system bonds directly to sound masonry and resists water as a physical barrier. A cavity drain membrane system leaves a studded membrane on the wall, collects any water that arrives in a perimeter drainage channel and discharges it, usually to a sump and pump or to a suitable drain. The right choice depends on the structure, the water table, the finish you want and what the room will be used for. This is the service for damp cellars being brought back into use, basement conversions creating habitable rooms, lightwells and vaults, garages and stores below ground, and basements where a previous coating or paint has already failed. It needs a specialist because below-ground water does not forgive detailing. Wall-to-floor junctions, service penetrations, steps and returns are where systems fail, and accredited materials only carry their guarantees when installed the way the manufacturer specifies. ### Who it is for Owners of damp cellars, basement flats, vaults and below-ground stores, and anyone converting a basement into usable living or working space. ### When it is needed When water enters at or below ground level, when a floor or wall is permanently damp, or before a basement is finished, insulated or fitted out. ### Why it needs a specialist System selection and detailing decide whether it works. Paint-on products sold for cellars fail under hydrostatic pressure. What happens if it is left ## An untreated basement gets worse in every direction Below-ground damp does not stay below ground. Moisture moves up into the structure above, salts build on wall surfaces, air in the room stays humid and the space becomes unusable for storage, let alone habitation. Anything organic stored there: boxes, timber, furniture, flooring; is gradually destroyed. The reliable way to waste money here is to treat a hydrostatic problem as a surface problem: waterproof paint, a skim of render, or insulated plasterboard fixed straight to a wet wall. Water under pressure lifts coatings off, and dry-lining a wet wall creates a warm, hidden void where mould and rot develop out of sight. ### Coatings blow off the wall Waterproof paints and thin coatings cannot resist hydrostatic pressure. They debond, blister and peel, taking the plaster with them. ### Damage to fit-out Floor finishes, stud walls, insulation and joinery installed over an unwaterproofed structure all have to be ripped out again. ### Rot and mould behind linings Dry-lining a wet wall hides the problem while timber battens, boards and insulation decay behind it. ### Moisture rising into the house Persistent below-ground water feeds damp in ground-floor walls and floors above, spreading the cost of the repair. ### Lost space and lost value A wet basement is storage you cannot use. A dry, guaranteed basement is habitable floor area. ### Flood risk left unmanaged Without a drainage and pump route, groundwater surges after heavy rain have nowhere to go except the floor. Our process ## A fixed sequence, so nothing is guessed at 01 ### Inspection Free survey of the below-ground structure: wall construction, floor condition, water entry points, external ground and drainage, and any previous waterproofing attempt. 02 ### Diagnosis and system selection We establish how water is arriving and specify the appropriate system; cementitious tanking, cavity drain membrane, or a combination with drainage and pumping. 03 ### Preparation and installation Surfaces prepared, defective render and coatings removed, then the accredited Sovereign or Wykamol system installed with all junctions, penetrations and returns detailed correctly. 04 ### Drainage, testing and finishing Perimeter channels, sump and pump where specified, system checked in operation, then finishes applied so the room is ready for use. 05 ### Completion and guarantee Balance due on completion, with the 10-year workmanship guarantee and 10-year QANW insurance-backed guarantee documentation issued. What you get ## The result you are paying for ### Usable floor area A dry, finished basement becomes a room; utility, gym, office or storage you can actually trust with your possessions. ### Water managed, not resisted by luck Systems are chosen for the water conditions present, so performance does not depend on a dry winter. ### Accredited systems and detailing Approved Sovereign and Wykamol contractor. Junctions, penetrations and returns detailed to the manufacturer's specification. ### Ten-year cover, twice over A 10-year company workmanship guarantee plus a separate 10-year QANW insurance-backed guarantee. ### Protects the structure above Controlling below-ground water stops it feeding damp into ground-floor walls and floors. ### Fixed price before work starts A defined scope and a fixed sum, paid 50% deposit and 50% on completion by bank transfer. Never a day rate. In detail ## Waterproofing systems, materials and variations Below-ground waterproofing is specified around three things: the water conditions, the structure and the intended use of the room. The materials follow from those decisions. ### Cementitious tanking (barrier protection) A cementitious tanking system is a polymer-modified, sand and cement based slurry or multi-coat render applied directly to prepared masonry or concrete, forming a barrier that resists water under pressure. It bonds to the substrate, which means the substrate must be sound, clean and free of old paint, bitumen and friable render before application. Barrier tanking suits structures in good condition where the finish needs to be solid, walls that will be plastered and decorated, or areas where the room dimensions cannot afford the build-up of a membrane system. It relies completely on detailing: wall-to-floor fillets, service penetrations, steps and reveals all have to be formed correctly, and a single missed junction is where water will find its way through. ### Cavity drain membrane systems (drained protection) A cavity drain membrane is a studded high-density polyethylene sheet fixed to the wall with sealed plugs and tapes. Water reaching the structure runs down behind the studs into a perimeter drainage channel and away to a sump chamber with a pump, or to gravity drainage where levels allow. The membrane is not trying to hold water back; it is redirecting it. This approach tolerates a wetter, less predictable structure and remains serviceable, which is why it is the common choice for basement conversions and older brick cellars and vaults. Wall membranes can be dry-lined or plastered over with a meshed membrane, and floor membranes sit under a screed or a floating floor build-up. ### Sumps, pumps and drainage Where water cannot discharge by gravity, a sump chamber and pump handle it. Specification decisions include pump capacity for the volumes expected, twin pumps or a battery backup where failure would flood a habitable room, and a discharge route that is both legal and practical. Externally, the volume of water arriving can often be reduced first: clearing and repairing rainwater goods, correcting ground falls away from the building, and repairing external drainage all cut the load on the system inside. ### Basement conversions and habitable rooms Turning a cellar into a habitable room brings in more than waterproofing: floor levels and headroom, insulation, ventilation, drainage for a WC or utility, electrics and escape routes all interact with the system chosen. Waterproofing is designed first, because every other element is fixed to or through it. Where a conversion is part of a bigger project, we can carry out the associated building, plastering and remedial work alongside the waterproofing so one contractor is responsible for the sequence rather than three. ### Residential and commercial applications Domestic work covers Victorian cellars, basement flats, vaults under pavements, garages and store rooms. Commercial work covers basement plant rooms, storage areas, retail stockrooms and offices, where protecting stock and equipment and keeping the premises trading shape the programme. In both cases the technical answer is the same: identify the water conditions, specify a barrier or drained system accordingly, detail it properly, and back it with guarantees. ### Cost and pricing There are no published prices, because the variables are large: area of wall and floor, condition of the substrate, whether pumping is required, how much preparation and removal of previous coatings is needed, access for materials and spoil, and the finish specified. The free survey produces a written fixed price for a defined system and scope, so you can see exactly what is included before committing. Carried out across Harrow, Chiswick, Isleworth, Chelsea, Pinner, Stanmore, Edgware, Ealing, London, Middlesex, Watford, Buckinghamshire, Slough, Brent, Surrey, High Wycombe, West London, see the full list of areas covered. Questions ## Waterproofing & tanking, common questions How much does basement waterproofing cost in London?It varies widely with the area treated, the system specified, whether a sump and pump are needed and how much preparation the structure requires. We survey free of charge and issue a written fixed price for the defined scope. How long does a cellar or basement take?Small cellars are typically a week or so; full conversions with drainage, pumping, screeds and finishes run longer. Your quotation sets out the programme before you commit. Is tanking or a membrane system better?Neither is universally better. Cementitious tanking suits sound structures needing a solid bonded finish; cavity drain membranes suit wetter, less predictable structures and conversions. The survey determines which fits your basement. Is waterproofing guaranteed?Yes. Waterproofing carries a 10-year company workmanship guarantee and a separate 10-year QANW insurance-backed guarantee. How long does a waterproofing system last?Correctly specified and installed accredited systems are long-term installations, which is why they are backed by ten-year guarantees. Drained systems include serviceable components, pumps and channels, that should be checked periodically. Can I fit out or dry-line the basement afterwards?Yes, and that is the normal sequence: waterproofing first, finishes second, with all fixings and penetrations planned so nothing compromises the system. Will you need to dig outside?Usually not. Most of this work is carried out internally. External drainage or ground-level corrections are recommended where they will meaningfully reduce the water reaching the structure. My cellar was painted with waterproof paint and it is peeling. Can you fix it?Yes. Failed coatings are removed as part of preparation, because no system bonds reliably over them. That is a common starting point for this work. Do you carry out urgent work where water is coming in now?Call us Monday to Friday 8am to 8pm or Saturday 8am to 1pm and describe the situation. Active ingress into a basement is prioritised for survey. Which areas do you cover for basement work?London, Middlesex, Watford, Buckinghamshire, Slough, Brent, Surrey, High Wycombe and West London. Free survey ## Get your cellar surveyed and a fixed price for a dry basement Tell us where the water appears, how bad it gets after rain and what you want to use the space for. We will survey it free of charge, specify the right system and quote a fixed price. - Free survey, diagnosis and written fixed-price quotation - 10-year company workmanship guarantee on damp treatment - 10-year QANW insurance-backed guarantee - Sovereign & Wykamol approved contractor - £2,000,000 public liability insurance Call 07576 573615 Related services ## Work that often goes with it ### Damp surveys & diagnosis Find out exactly what is causing the damp, what it takes to fix it, and what it costs, in writing, at a fixed price, with no charge for the visit and no obligation to proceed. Damp surveys & diagnosis in London & Middlesex ### Rising damp treatment A failed damp proof course is diagnosed, treated with an accredited Sovereign or Wykamol system and replastered to a decoration-ready finish, priced as a fixed sum before any work starts, and guaranteed for ten years. Rising damp treatment in London & Middlesex ### Small refurbishment & remedial works Treatment stops the damp; remedial work makes the room liveable again. Plaster, joinery, floors, decoration preparation and making good, completed by the contractor that did the specialist work, at a fixed price. Small refurbishment & remedial works in London & Middlesex ### Structural waterproofing & tanking in the areas we cover Structural waterproofing & tanking in HarrowStructural waterproofing & tanking in PinnerStructural waterproofing & tanking in StanmoreStructural waterproofing & tanking in EdgwareStructural waterproofing & tanking in EalingStructural waterproofing & tanking in ChiswickStructural waterproofing & tanking in IsleworthStructural waterproofing & tanking in ChelseaStructural waterproofing & tanking in MiddlesexStructural waterproofing & tanking in BrentStructural waterproofing & tanking in LondonStructural waterproofing & tanking in West LondonStructural waterproofing & tanking in WatfordStructural waterproofing & tanking in SloughStructural waterproofing & tanking in BuckinghamshireStructural waterproofing & tanking in High WycombeStructural waterproofing & tanking in Surrey All damp proofing & building servicesRising damp treatmentPenetrating damp treatmentDamp surveys & diagnosisPlasteringRenderingBrickworks & repointingDamp proofing project photographsBook a free damp survey Damp proofing, structural waterproofing and remedial building works across London and the surrounding counties. Tom Charge, Owner. ### Contact - 07576 573615 - tom@cbsdamp.co.uk - C/O MG Tax, 166 College Road, Harrow, England HA1 1BH ### Hours - Monday8am – 8pm - Tuesday8am – 8pm - Wednesday8am – 8pm - Thursday8am – 8pm - Friday8am – 8pm - Saturday8am – 1pm - SundayClosed ### Guarantees - 10-year company workmanship guarantee - 10-year QANW insurance-backed guarantee - 6-month guarantee on building work - Sovereign & Wykamol approved contractor - £2,000,000 public liability insuranceAboutServicesAreasOur workContact ### Damp proofing & building services - Rising damp treatment - Penetrating damp treatment - Damp surveys & diagnosis - Structural waterproofing & tanking - Plastering - Rendering - Brickworks & repointing - Brick stitching - General building - Small refurbishment & remedial works ### Areas we cover - Harrow - Pinner - Stanmore - Edgware - Ealing - Chiswick - Isleworth - Chelsea - Middlesex - Brent - London - West London - Watford - Slough - Buckinghamshire - High Wycombe - Surrey © 2026 Charge Building Services Ltd. 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