Solving Damp

Damp is something that we have almost come to expect in old houses, and for renovators it is certainly not an uncommon problem to have to remedy. The key to successfully eliminating it from a building – and to keeping it damp-free – is to identify what type of damp you are dealing with and what is causing it. Damp most often comes in three forms:

Penetrating Damp

Identifying: Tell-tale signs include discoloured tidemarks in line with the external ground level on interior walls; blistering, salting and disintegration of plasterwork; rotting skirting and floor boards; damp patches on the wall that do not dry out; and mould growth to the walls.

Causes: Penetrating damp is caused by water coming into the house from outside through the walls. There are many ways in which this can happen, including building defects such as faulty roof coverings, cracked brickwork, poorly fitted windows and door frames and inadequate guttering.

Piling up external ground above internal floor levels will also cause problems (also a factor in rising damp issues).

Treatment: Find the source and deal with the problem. To find the source, examine gutters, downpipes, flashing, cracked render and window/door frames — these are the most common areas where water can ingress into the home.

Condensation

Identifying: The problem will be pretty obvious with water running down windows. Worse cases can be identified by water running down walls and dark mould spots, ranging from small speckles to big patches on ceilings and walls. Not only does this mould look unsightly, but it also releases spores which can seriously affect people with respiratory complaints.

Causes: The amount of water carried in the air varies depending on the air temperature. Hot air is able to carry more water than cold air, and as the air within a house is fairly warm, it contains a considerable amount of water vapour. Condensation occurs when this warm air comes into contact with cold surfaces, such as windows and some outside walls, and the water held in the air can no longer be supported. The water condenses as liquid on the cold surfaces. Insufficient ventilation is one of the main causes, as are badly insulated walls. Rising damp can also be a cause as it increases the amount of moisture in the air. Although single glazing is not exactly a cause, those who have it will usually notice some condensation due to the fact that the glass in these windows can be as cold as the outside temperature.

Treatment: There are a number of factors that can contribute to condensation, and, therefore, a number of treatments and control methods. You can control condensation through better ventilation, reducing the amount of water vapour (e.g. steam from showers) that travels through the house and so on. A mechanical ventilation system may help in this regard. Upgrading heating and insulation in the home also helps, as it reduces the amount of cold walls on which water vapour can gather.

Rising Damp

Identifying: Rising damp can be suspected when paint will not adhere to a wall; wallpaper lifts off and stains appear; plaster flakes away and feels spongy and soft to the touch, and bubbles and white powder or crystals will also be visible. You will also find that skirting boards and floorboards will have rotted. Outside, it will be obvious from the mortar between bricks fretting and falling out. Stains and white powder will appear on brickwork, too. Usually the height of the damp will not rise above 450mm, so any damp patches above this can be consigned as penetrating damp. Salt deposits are sometimes found higher in the wall.

Causes: This form of damp occurs when water rises up vertically through the wall due to the deterioration or removal of the damp-proof course (dpc) – particularly where there are concrete floors internally – or, in some cases, the complete lack of a dpc. Water ingresses, then rises through the pores (sometimes known as capillaries) in the masonry, seeking a means of evaporation. The brickwork acts a bit like a wick, sucking up the water. Another common cause is ‘bridging’, where the external ground up to the building’s walls is above dpc level.

Treatment: Before you do anything, try digging out any soil or debris which comes up higher than the dpc level. You might just find that this stops the problem from getting any worse and all that will be required is some repair work. If it is impossible to dig away the ground, a French drain – a ditch covered with gravel around the perimeter of the house – might be the solution.

Check your damp-proof course. In the past a whole range of materials were used to construct a dpc — stone, slate, lead, zinc, stainless steel and, more recently, plastic. Once the building is built it can be hard to insert a whole new dpc, although there are methods out there, such as a technique which involves inserting sheets of stainless steel into saw-cut slots. These techniques are best left to the professionals.

Other methods involve injecting a chemical damp proof course into the wall designed to prevent water getting in (though this treatment is not suitable for all old homes, so seek professional advice first). Amongst these are chemical water repellents in the form of liquids, gels, pastes and creams, some of which can be injected on a DIY basis (a dpc Injection Kit is available from HSS Hire for around £60 for a weekend, hss.com). The cream-based injection method is a quick and neat process. A series of small holes are drilled around 150mm above ground level in the exterior walls before the chemical is injected. The holes are filled and the result is not at all obvious. If the plaster is sound, it may even be able to stay on the walls internally. Do remember, however, that rising damp usually brings with it soluble salts into the plasterwork and, even after the wall has dried out, these will still attract moisture. You might find that salt-neutraliser liquid can deal with minor patches of salt.

‘Pore blocking’ is another technique, where a cement-based mortar is injected — again, a job best left to the professionals.

At the more expensive end of the scale is the ‘osmotic’ system. This can only be carried out by professionals and involves running a titanium wire, connected to a mains-powered control box, around the walls. Wire loops are inserted into large holes drilled into the walls and the whole system is earthed. The electricity from the mains supply passes through a transformer, through the anodes and to earth, which forms an electrical field which repels damp.

Modern Living in Old Houses

Funnily enough, it is often modern technology which causes damp problems in old houses — if we just left them alone, they would be fine, although perhaps not that comfortable to live in. Old houses would once have been draughty places featuring open fires and chimneys, and were built from porous materials, such as brick, stone and lime. This meant that they were very well ventilated, so no damp – or heat – hung around for long. These days we often aim to seal up our homes from the elements, with double glazing and loads of insulation. Although these provide a comfortable living environment, it does mean that steps have to be taken to adequately ventilate the building.

Further reading:

• Damp Checklist
• Eliminating Damp
• How to Assess a Potential Renovation Property