Damp & Mould:
You may have seen or heard of the 1970s TV series Rising Damp, which featured a landlord and his tenants (lodgers in this case) which rather implies that all rental properties are troubled with this kind of damp.
Far from the case, but some are. In fact the problem can affect any property, rental or not. Rising damp, penetrating damp and condensation are the three most common types of damp that can affect a home. All are undesirable and all can have health and safety issues attached to them.
Each of these needs to be identified and then treated in different ways, and the costs can vary dramatically, so it’s important to know what type of damp is affecting a property before you try to get it fixed.
This article deals with Rising Damp, while others in the series will deal with penetrating damp and condensation.
This image below shows a typical case of rising damp on an internal wall. Always at ground level the dampness will either leave a tide mark on plaster, or as in more advanced cases like this, will actually deteriorate or destroy the plaster and masonry over time.
With your tenants living in a property with damp and mould it can be bad for their health, so it’s important to get it sorted as soon as possible. The worse the situation gets and the longer it goes on, the more likely it is to do extensive damage which will cost more to remove and adequately repair in the end.
Rising damp is caused by ground water moving up through a wall or floor by capillary action. Soft materials such as some brick will transmit moisture far more effectively than will had stone such as slate or granite. Most walls and floors would allow some water in, but it’s usually stopped from by a barrier called a damp-proof course (DPC) or damp-proof membrane (DPM).
A damp-proof course in a wall is a horizontal strip, usually made from plastic, or bitumen felt, or in older properties sometime slate, built into the wall at the height of around 5cm above ground level.
A damp-proof membrane is a sheet of material (Visqeen), impervious to water, laid under a concrete or other type of solid floor. This should be connected to the damp-proof course so that the house is effectively sealed and protected from ground water.
Laid below an insulation layer, this barrier not only prevents water ingress, it can act as a barrier to Radon gas, and the insulation keeps the floor material warm and prevents condensation forming on the floor.
Very old building may not have any of this, so walls and floors can not only suffer from rising damp, flag floors, which they often were in old buildings, also suffer from condensation when warm air strikes the cold floor in cold weather.
Newer houses will have all the damp proofing and insulation features as this is part of building regulations (Part C for England and Wales), but older buildings, in particular those built prior to the building regulations of 1875, will almost certainly not have.
A common cause of rising damp in a wall can be when the level of the ground on the external wall is allowed to rise higher than the damp-proof course, or there is inadequate drainage allowing water to soak masonry, thereby bridging the damp course.
Obvious symptoms of rising damp will be a tide-line on plaster or wallpaper low down the ground-floor walls, damaged skirting boards (sometimes with wet and dry rot) and decaying plaster and masonry. The damp will often dissolve soluble salts from the ground and building materials, which then crystallise, forming a white powder-like substance above the ground.
Watch this video on Rising Damp by The Property Care Association, the UK’s trade body representing structural repair, damp proofing, timber preservation, structural waterproofing and flood remediation provide an insight into the much debated issue of rising damp.
Repairs for Rising Damp
First, check if there is a damp-proof course (DPC) and damp-proof membrane (DPM), which should prevent groundwater rising and soaking into ground level walls or floors. If a DPC is present you will see a thin strip of usually darker material one or two courses up from ground level on the outside of the walls. It will be more difficult to tell if there is a DPM but damp floors will indicate if one is not present or it is damaged.
Make sure the outside ground soil is well below the DPC and if necessary dig a drain channel to make sure. Otherwise, with rising damp in walls the cure is usually to replace the DPC or use a silicone injection system which make the building materials themselves impervious to water.
In the case of floors, this may entail removing a solid floor and installing a new DPM and floor insulation before relaying concrete. Obviously this is expensive but if done properly, with the membranes interlinked, it’s a very satisfactory solution.
Small patches of damp on a floor may be rectified by painting over it with two coats of bitumen latex waterproof emulsion underneath the floor covering. This can be backed-up with a layer of reflective foil building paper (foil-side up). But for extensive damp on floors the only satisfactory solution is a floor re-lay.
Tanking walls and floors in damp-proof materials is a building process that effectively means sealing it to protect it from moisture, usually when walls and floors are below ground level, such as in basements.
Tanking is usually done to walls and floors which are damp by producing an asphalt barrier or “sandwich” under the plaster or a wall or under the concrete of a floor; a thick liquid asphalt sealed membrane.
As all this work can be expensive, so it’s worth getting a few professional opinions to help you decide what course of action to take. And remember, this is an area where rogues and charlatans operate, so make sure you are dealing with reputable firms.