Damp Proofing

Damp Proofing

Structural dampness is the presence of unwanted moisture in the structure of a building, either the result of intrusion from outside or condensation from within the structure.

A high proportion of damp problems in buildings is caused by condensation, rain penetration or rising damp.

Dampness tends to cause secondary damage to a building. The unwanted moisture enables the growth of various fungi in wood, causing rot or mould health issues. Plaster and paint deteriorate and wallpaper loosens. Stains, from the water, salts and from mould, mar surfaces.

Externally, mortar may crumble and salt stains may appear on the walls. Steel and iron fasteners rust. It may also cause a poor indoor air quality and respiratory illness in occupants. In extreme cases, mortar or plaster may fall away from the affected wall.


Materials widely used for damp proofing include:

  • Flexible materials like butyl rubber, hot bitumen, plastic sheets, bituminous felts, sheets of lead, copper, etc.
  • Semi-rigid materials like mastic asphalt
  • Rigid materials like impervious bricks, stones, slates, cement mortar or cement concrete painted with bitumen, etc.
  • Stones
  • Mortar with waterproofing compounds
  • Coarse sand layers under floors
  • Continuous plastic sheets under floors

Investigation & Treatment

  • The first step in assessing damp is to check for standing water.
  • Removing water with good drainage will remove any form of dampness.
  • Once done, and dampness remains, the next step is to look for the presence of a damp-proof course (DPC). If a damp-proof course is present, it is likely to be functioning, as the materials from which damp proof courses are manufactured tend to have a long lifespan.
  • However, it should be acknowledged that there are cases where existing damp proof courses fail for one reason or another.

Damp Proofing Procedures

Damp proofing is accomplished in several ways including:

  • A damp-proof course (DPC) is a barrier through the structure by capillary action such as through a phenomenon known as rising damp. The damp proof course may be horizontal or vertical. A DPC layer is usually laid below all masonry walls, regardless if the wall is a load bearing wall or a partition wall.
  • A damp-proof membrane (DPM) is a membrane material applied to prevent moisture transmission. A common example is polyethylene sheeting laid under a concrete slab to prevent the concrete from gaining moisture through capillary action. A DPM may be used for the DPC.
  • Integral damp proofing in concrete involves adding materials to the concrete mix to make the concrete itself impermeable.
  • Surface coating with thin water proof materials for resistance to non-pressurized moisture such as rain water or a coating of cement sprayed on such as shotcrete which can resist water under pressure.
  • Cavity wall construction, such as rainscreen construction, is where the interior walls are separated from the exterior walls by a cavity.
  • Pressure grouting cracks and joints in masonry materials.

Protect your home from the elements by Damp Proofing

Damp is usually caused by excessive condensation; water penetration into the plaster and brickwork of internal walls extracts salts which appear as unsightly white deposits known as efflorescence. The leaks also result in unattractive 'tide marks' appearing on the interior side of the wall, which can often spread rapidly and severely damage the structure and safety of the wall itself. Damp also rots wooden fittings and furniture and can loosen wallpaper, plaster and paintwork.

Although many buildings should have been damp proofed before purchase it's often the case that previous home owners or contractors skipped over the problem rather than dealing with it straight away, meaning your walls aren't built with the correct non-porous material or haven't been sufficiently waterproofed. To deal with the problem before it gets too serious you should always keep rooms, especially those below ground level, well ventilated; mould should be scrubbed away carefully (always wear gloves) and you can check for leaks in gutters and down-pipes yourself. Before the situation gets to the point where the building or you and your family's health is at risk, you should always have the property professionally damp proofed.

Call Damp Guru today!

Thermal Solutions

Thermal Scanning

Thermal images can detect water and moisture the naked eye cannot see:-

  • Prevent Health Damaging Mould Growth before it appears
  • Can assist with finding the origin of the leak

Benefits of using thermal scanning

  • It can identify otherwise unseen areas of water or moisture ingress
  • It uses non–invasive testing methods
  • Findings are presented as a clear images
  • Includes analysis and photos in a detailed report

Thermal Scanning can also be used for:-

  • Energy and Heat loss Audits
  • Electrical and Mechanical Inspections
  • Damp proofing is another aspect of waterproofing. Masonry walls are built with a damp-proof course to prevent rising damp, and the concrete in the foundation needs to be damp-proofed or waterproofed with a liquid coating, basement waterproofing membrane (even under the concrete slab floor where polyethylene sheeting is commonly used), or an additive to the concrete. A potential problem in earth sheltered houses is too much humidity, so waterproofing is critical in these houses.

The penetrations through a building needs to be built in a way such that water does not enter the building, such as using flashing and special fittings for pipes, vents, wires, etc. Some caulking's are durable, but many are not a reliable method of waterproofing.

Rainwater Damage

Water penetrates the structure if there are no gutters and downpipes; rainwater courses off the roof, down walls and enters through weak plaster or badly jointed bricks. It has to be ensured that earth or paving falls away from the building and that there is adequate allowance for water run-off.

If there is a high water table it is necessary to incorporate plastic sheeting under all floor concrete.

Masonry Construction

A DPC is a durable, impermeable material such as slate, felt paper, metal, plastic or special engineered bricks bedded into the mortar between two courses of bricks or blocks. It can often be seen as a thin line in the mortar near ground level. To create a continuous barrier, pieces of DPC or DPM may be sealed together. In addition, the DPC may be sealed to the DPM around the outside edges of the ground floor, completely sealing the inside of the building from the damp ground around it.

Concrete Walls and Floors

Concrete normally allows moisture to pass through a vertical damp proof barrier. Barriers may be a coating or membrane applied to the exterior of the concrete. The coating may be asphalt, asphalt emulsion, thinned asphalt called cutback asphalt, or a rubber polymer. Membranes are rubberized asphalt or epdm rubber (ethylene propylene diene terpolymer - an extremely durable synthetic rubber roofing membrane). Rubberized products perform better because concrete sometimes develops cracks and the barrier does not crack with the concrete.

Types of Damp

Rising Damp

In the most simple terms, rising damp is a condition where moisture from the ground travels up through the pores in the bricks and mortar of a building, much in the same way that oil travels up through the wick of an oil lamp; once rising damp has become established, this moisture can cause problems such as damp patches on walls, peeling paint and wallpaper, and eventually plaster falling away from the wall. Over time it will lead to structural damage to the building if left unchecked.

The symptoms of rising damp can often be confused with the symptoms of other damp problems such as lateral damp and condensation. These types of dampness require different methods of treatment, so it is essential that Damp Guru is consulted to diagnose the type of dampness to be treated.

Many misdiagnose a wall stain as rising damp due to misinterpreting the visual evidence of the wall and the readings of moisture meters.

Lateral Damp

Lateral damp is caused by: The ground level being higher on the outside of the wall, this allows the moisture from the soil on the opposite side of the wall to penetrate through the wall causing damage to the internal wall.

A common cause of penetrating damp is the incorrect installation, deterioration or omission of the vertical damp course.

Evidence of penetrating lateral damp:-

  • Paint flaking
  • Bubbling paint
  • Discolouration of paint
  • Efflorescent salting present on the surface

Treatment includes tanking and possibly chemical injection as well, if necessary.

Why has Rising Damp occurred in My House?

The problem of rising damp has been known for at least 100 years. Therefore, it has been common building practice for some time to install a damp proof course whenever a house is built. In a typical solid floor construction, the DPC usually consists of an impervious barrier around the whole building, set into the mortar bed just above the floor level. This DPC can become ineffective for a number of reasons:

  • The original builder forgot to install a DPC.
  • The original DPC was not positioned correctly.
  • The original DPC has deteriorated due, for example, to house settlement, vibration, from passing traffic, or general land subsidence. This is especially common where a Bitumen DPC has been used.
  • The DPC has been "bridged" e.g. by earth being piled up against an outside wall.

Damp can cause structural problems and pose serious health risks – so make sure your home is damp proofed properly now.

Hygroscopic salts, made up of chlorides and nitrates, are transported to the wall surface by the moisture; these alkaline salts react with acidity in the air caused by factory and vehicle emissions, attacking the cement and sand in mortar between the bricks and the bricks and plaster on the walls. The salts multiply and expand with moisture in the air and cause the masonry to crumble and eventually structural failure will occur.

Even if not evident or visible the presence of damp or water penetration can be established with a damp meter.

A damp meter has 2 pins which pressed onto a surface gives the percentage of damp in a structure. Other types can be held against the surface and give a reading. Anything above 10% could be harmful.

If the rising damp is to be eliminated, it is essential that the precise cause of the breakdown in the DPC is established.

Contact us for an obligation free Quotation.