Waterproofing a Basement – The Homeowner’s Guide

Waterproofing a Basement – The Homeowner’s Guide

3rd July, 2025

Many London homes have underground living space; some are wine cellars, some offices and some are rented out as flats, whatever you use it for, a basement needs to be waterproof, especially if your home happens to be on one of the huge clay beds in the Thames Valley Basin.

In this article, we outline the two most popular methods to waterproof a basement.

Basement Tanking

This is a term used when the walls are coated with a waterproof render such as Sika, the empty basement would be prepared and several layers would be applied, also on the ceilings and floors to create a watertight space. Adequate ventilation is required and regular checking of humidity levels. This is the preferred solution to mild damp issues and there is top-rated basement tanking in London from specialists that offer a 30-year guarantee on all their work. If you think damp could be present in your basement, contact London Damp Surveys and if there are damp issues, we will find them.

Type C Cavity Drainage Systems

Generally, the most popular, installing a cavity membrane with channels to a sump area where water can be pumped to designated drainage points. Studded membrane is fitted to the floor, walls and ceiling, allowing water to drain away without damaging the structure. This is definitely specialised work, so you should use an accredited damp-proofing company, one that offers long-term warranties on their work. Installing a drainage system is usually the first priority, then surfaces are prepared for the studded membrane and all seals are in place. There is a sump area and a small pump to direct the water to the main drains, making it ideal for areas where water collects; if you would like your basement inspected for damp and mould, we at London Damp Surveys can send one of our certified surveyors to your home. Consult with the experts to get it right the first time; we have a working relationship with the best damp-proofing outfit in London and they guarantee their work for 30 years, which brings peace of mind.

Avoid Costly Repairs

If damp is not treated, it can quickly lead to very costly repairs, you might have to vacate the property until the damp-proofing work is completed. In the event you are planning to buy a property with a basement, we recommend having the property surveyed for damp, mould, condensation and timber rot. It is easy to conceal damp issues with a few coats of paint and waterproof plaster and when we survey a building, you receive a detailed report on every aspect of the property. Our pre-purchase damp survey is designed to identify any damp, mould or condensation; you receive a detailed report within one day of the survey being completed.

Don’t delay, call London Damp Surveys on 0207 305 5997 and have your basement inspected by a qualified damp surveyor.

Damp Survey Costs

Transparent pricing with no hidden fees for our independent, unbiased surveys.

Level 1

Level 1

£199 + VAT

What’s included:

  • Inspection of walls
  • Inspection of floors
  • Inspection of ceilings
  • Leak inspection of drains and plumbing
  • Damp information and prevention guide
Level 2

Level 2

£299 + VAT

What’s included:

  • Everything in Level 1
  • Dry rot inspection
  • Wet rot inspection
  • Woodworm inspection
  • Damp information and prevention guide

 Survey Add Ons

Add On 1

£299 + VAT
Lab Analysis Of Plaster

Laboratory analysis Of plaster identifies hygroscopic salts such as chlorides and nitrates. which indicate whether damp is caused by rising groundwater or by plumbing leaks, This testing removes guesswork, allowing the exact source of moisture to be identified so the correct treatment is applied rather than carrying out unnecessary damp-proofing work.

Add to Survey

Add On 2

£299 + VAT
Mould Lab Swab Testing, qPCR on DNA

qPCR DNA mould testing detects microscopic mould spores that are invisible during a normal inspection and van remain hidden behind walls, floors. or inside building rkaterials. It identifies the exact mould species present and the contamination level, allowing hidden mould problems to be confirrned and properly treated before they affect the property or occupants’ health.

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Qualifications: All our surveyors are PCA and CSRT qualified for remedial treatments and also CSSW qualified for structural waterproofing.
Next day report: You will receive the report within 24 hours of the inspection taking place.

These are the tools we use

A damp meter

A damp meter

A damp meter is a diagnostic tool used to detect and measure moisture levels within building materials such as plaster, brick, timber, and concrete.

Borescope camera

Borescope camera

borescope camera is a small inspection camera attached to a flexible semi-rigid cable that allows you to see inside areas that are otherwise inaccessible.

Inspection Drone

Inspection Drone

A drone is a remotely operated aerial device equipped with a camera that allows visual inspection from above without the need for scaffolding or ladder.

Air Humidity Sensor

Air Humidity Sensor

Air humidity sensor measures the amount of moisture present in the air, expressed as relative humidity (RH) in percentage. It helps determine whether indoor conditions are contributing to condensation, mould growth, or damp-related issues.

Thermal Imaging Camera

Thermal Imaging Camera

A thermal imaging camera detects temperature differences on surfaces by using infrared technology to produce a heat map image. In damp investigations, it helps identify cold spots, moisture intrusion, insulation defects, thermal bridging and leaks.

Air Flow Ventilation Detector

Air Flow Ventilation Detector

An air flow ventilation detector measures the movement and volume of air passing through vents, extractor fans, and air bricks. It confirms whether ventilation systems are working properly and achieving adequate air changes within a room. Poor airflow leads to trapped moisture, high humidity, condensation on cold surfaces, and ultimately mould growth.

Mould Swab Test Kit

Mould Swab Test Kit

A mould swab test is carried out to confirm the presence of hidden mould growth and identify the specific species involved. Surface mould is not always visible, especially behind furniture, inside cavities, or within ventilation systems. Laboratory analysis of a swab sample determines whether active mould spores are present and what type they are, which helps assess potential health risks and decide the correct remediation approach rather than relying on visual assumption alone.

Plaster Salt Analysis Lab

Plaster Salt Analysis Lab

Laboratory analysis of plaster is used to identify the type of salts present within the material, typically chlorides and nitrates. The presence and concentration of these salts help determine whether the moisture source is consistent with rising damp, ground contamination, or another forms [sic] of water ingress. such as mains water leak, This removes guesswork and prevents misdiagnosis, ensuring the correct remedial treatment is specified rather than applying unnecessary or ineffective solutions.