Damp Proofing & Waterproofing FAQs

Damp in homes is very common. The main causes are poor maintenance, inadequate ventilation and, in older properties, raised ground levels or the lack of an effective damp proof course.

Modern houses with poor ventilation, combined with limited heating, often suffer condensation problems. Some properties were built without a damp proof course, and where one exists it may no longer work fully because of changes in ground levels, damage during renovations, or simply age.

A DPC is a barrier built into the base of a wall to stop moisture rising from the ground. Older properties were not usually built with one; they became common from around 1875.

Older courses were often slate, while modern construction uses plastic. When a new DPC is installed as a remedial measure, it is usually formed by drilling the wall and injecting a waterproof liquid or high-strength chemical cream that creates a new barrier. Left untreated, rising damp can decay timber in contact with the walls and damage plaster and decoration.

Most properties have had some form of damp treatment in the past, but it may no longer meet modern standards. Renovations often damage existing damp proof courses or remove previous waterproofing, and new driveways or patios can bridge an old DPC by raising ground levels.

Many basements and cellars are also being converted into usable space, where previously they were coal stores or left empty. If you are unsure whether your property has adequate protection, book a survey.

Different types of damp show themselves in different ways, but common signs include:

• A damp or musty smell
• Excessive condensation on windows
• Tide marks on walls
• Peeling wallpaper or paint
• Discoloured or dark patches on floors, walls and ceilings
• Mould or mildew growth

It depends on the problem, the original construction (brick, stone and so on) and the arrangement of ground levels and drainage. We carry out damp proof injection using silicone DPC and thixotropic creams, salt-retardant waterproof rendering, and structural waterproofing systems. A survey identifies the right method for your property.

New damp proof course installations carried out by our team are guaranteed for 20 years. If a problem recurs, contact us and we will arrange a re-inspection under the terms of the guarantee. If our work is found to be at fault we will re-treat the area, and if there is another cause we will identify it and advise you on the right course of action.

Diagnosing damp yourself can prove expensive, because the wrong diagnosis or treatment can cause structural damage and cost far more to put right. Effective treatment starts with correctly identifying the source and cause; if that step is wrong, the treatment usually fails.

Our surveyors have decades of experience finding the source, cause and most effective treatment for damp problems, so we always recommend speaking to a specialist before committing to any work.

Usually not. Once plaster is damaged and contaminated with salts it needs to be replaced. Some systems do not require removal, but plaster removal is necessary for certain treatments, such as tanking plastered over as part of a rising damp repair.

Allow the walls to dry out for as long as possible before redecorating. Drying time depends on ventilation, the extent of the damp and the room temperature. We usually advise waiting at least two to three weeks after plastering or rendering, then using a vapour-permeable, water-based microporous emulsion.

Typical signs of rising damp include:

• Wet patches on walls
• Flaky salts within the plaster
• Bubbling plaster
• A musty or damp smell
• Crumbling mortar between bricks
• Black mould

Our surveyors use a moisture meter to build a moisture profile, which, combined with experience, is usually sufficient. Rising damp is often misdiagnosed, which is why many treatments fail, so our FODCS certified surveyors are trained to diagnose it accurately.

Rising damp occurs when moisture from the ground travels upward through masonry by capillary action, where a damp proof course is missing or has failed. Standard bricks and mortar have a more open pore structure than engineering brick, which allows moisture to rise more easily.

It can be difficult to tell them apart, but there are some distinguishing signs.

Wet rot: black fungus on timber; spongy, soft, discoloured wood that cracks and shatters once dried out; and a damaged paint finish.

Dry rot: cracking along the grain with mycelium growth; a lime-yellow tinge under light; brown, crumbling timber; and sometimes large, flat, mushroom-like fruiting bodies.

Visual inspection alone is not always enough. Our FODCS certified surveyors carry out further investigation, including timber examination, to confirm the type and extent of decay.

Structural waterproofing protects below-ground spaces such as basements, cellars and lower-ground rooms from water in the surrounding ground. Unlike standard damp proofing, which deals with moisture in walls above ground, it manages the constant pressure of groundwater against the structure, and it is designed and installed to BS 8102:2022. You can read more about our structural waterproofing.

BS 8102:2022 defines three types of protection. Type A (barrier protection) is a tanking coating or membrane that resists water. Type B (structurally integral protection) uses the structure itself, such as water-resistant concrete. Type C (drained protection) is a cavity drain membrane that manages water entering the structure and channels it to a sump and pump. Many basements use a combination. See our guide to below-ground waterproofing systems.

Tanking (Type A) is a bonded coating that resists water by forming a barrier against the structure. A cavity drain membrane (Type C) takes the opposite approach: rather than resisting water it manages it, channelling any ingress behind a studded membrane to a drainage channel and sump pump. Tanking suits lower-risk areas such as storage cellars, while cavity drain systems are usually more reliable for habitable basements. Compare basement tanking and cavity drain membranes.

BS 8102:2022 is the British Standard for protecting below-ground structures from water. It recommends that waterproofing design is carried out by a suitably qualified specialist, such as a CSSW (Certificated Surveyor in Structural Waterproofing) holder. For mortgage or building warranty purposes, CSSW involvement is often required for a valid guarantee. Our structural waterproofing is designed to BS 8102:2022 by CSSW qualified surveyors.

Cost varies with the system, the size of the basement and the ground conditions. As a guide for residential properties, Type A tanking for a small cellar typically starts from around 3,500 pounds, while a Type C cavity drain system for a habitable basement typically falls between 6,500 and 12,000 pounds. We always survey and provide a fixed-price quote before any work begins. See basement waterproofing for more detail.

New waterproofing installations carried out by our team, including tanking, cavity drain membranes and structural waterproofing, are covered by a written 10-year guarantee. You receive the guarantee in writing along with your specification and completion documentation, which you can keep and pass on if you sell the property.

Yes. A Type C cavity drain membrane system is designed to manage active water ingress, channelling it safely to a sump and pump rather than trying to hold it back. We first survey to find the source and assess the structure, then specify the right system. Many of our projects involve basements with existing or historic water problems.

Every home produces moisture, for example when cooking, drying clothes indoors or bathing. Warm air holds more water vapour, and when it meets a cold surface such as a wall, window or mirror it turns to condensation droplets. Keeping the home warmer and better ventilated reduces condensation.

Occasional condensation is usually nothing to worry about, but if it happens often it can lead to damp issues and mould, both of which can affect your health and your property.

Ventilating regularly by opening windows and doors helps clear damp air and reduce condensation.

Wipe affected walls and windows with an HSE-approved fungicidal wash, following the safety instructions. Shampoo carpets and dry-clean affected clothing, and avoid using a vacuum or brush to remove mould. Redecorate with good-quality fungicidal-resistant products to help prevent it returning.

Anti-condensation or fungicidal paint is ineffective if covered with ordinary paint or wallpaper. The only lasting cure is reducing the condensation that feeds the mould.

Damp in general can aggravate respiratory issues, particularly for children, older people and those with allergies or asthma. Health problems specifically from penetrating damp are fairly rare, but where the damp is severe it can be harmful to the people living in the property.

The first step is to identify the source of the moisture and how the water is getting into the building. Then repair the defect, such as a leak or crack, to stop water entering, and finally make good any area damaged by the penetrating damp.

Yes. The cold internal wall surfaces caused by penetrating damp are prone to condensation and black mould. Poorly ventilated and under-heated spaces, and buildings with inadequate waterproofing, are ideal conditions for mould growth.

If you are worried about black mould in your property, call us on 0300 373 7251 and our damp specialists can advise on the right solution.