Home Improvement

What Is Rising Damp & How To Treat It

Rising damp is one of all talked about topic because it is within every house .This How To guide takes you through identifying rising damp, the causes and how to effectively deal with it. A big part on this guide is given over to effectively identifying rising damp in your home, telling it apart from much more common damp issues. We also bust some myths around growing damp and its treatment.

What is Rising Damp?
Rising damp is a relatively rare form of damp that affects the walls of buildings. It occurs when moisture from the ground travels up through the wall surfaces by capillary action. This means that ground water is effectively sucked up through tiny tubes in the bricks, just like a group of straws. This water contains salts that also travel up through the wall.

Around the affected wall, you get other porous building materials such as plaste rwork and the timber found in the ground boards, joists and skirtings. These materials will also absorb the ground water easily and you’ll find evidence of wet rot in the timber.

Generally rising damp is first noticed by the damage it causes to the inner walls of an building. Plaster and paint can deteriorate and any wallpaper tends to loosen. A obvious stain often appears on the wall by means of a tide mark at the point where in fact the ground water has reached. You may also see salts blooming on the internal surface. This is something often associated with rising damp and will lead to the debonding of paints and even plaster work. Externally, mortar may crumble and white salt stains can happen on the wall membranes. We will enter in the common signs of growing damp in greater detail later in the guide.

Causes of Rising Damp
Rising damp is a relatively rare form of damp that influences the walls of buildings. It occurs when moisture from the bottom travels up through the wall space by capillary action. This means that ground water is effectively sucked up through tiny tubes in the bricks, like a series of straws. This water contains salts that also travel up through the wall.

Around the afflicted wall, you get other porous building materials such as plaster work and the timber found in the ground boards, joists and skirting. These materials will also absorb the ground water easily and you’ll find proof of wet rot in the timber.

Sometime the DPC can remain intact, but the DPC can be bridged. That’s where the damp from the bottom has the capacity to travel up past the DPC due to a construction fault.

Examples of this include:

Debris in the wall cavity or sub floor void.
Internal or external renders / plasters overlapping the DPC
External ground levels being raised above the DPC.
Inappropriate insulation material in the cavity.
Solid floors

Rising Damp – Internal Walls
Most people first notice an issue with rising damp on internal walls. Rising damp often brings about tide marks on your internal walls up to the height where the water has reached. In most cases, these tide mark stains appear up to metre above the skirting board. In a few very rare cases, normal water can travel beyond this aspect.

The height the water reaches will depend on several key factors. Included in these are the pore structure of the bricks and mortar and the speed of evaporation. Masonry containing a high proportion of fine pores will allow water to rise higher than one with less pores. Rising damp can occur up to 1.5 metres and even higher in some very rare instances.

The water from the ground often contains salts that are then deposited on the wall when water evaporates. These salts can cause the paint to bubble and a white fluffy deposit to be left on the top. You will discover two main types of salt – sulphates which cause crusty white patches and invisible hygroscopic salts known as nitrates and chlorides. The hygroscopic salts continue to draw moisture and for that reason must be treated.

What causes rising damp in internal walls?
Rising damp in internal walls is caused by the same movement of ground water up through the brickwork by capillary action. It is the reaction to a failed or non-existant DPC or when the DPC has been bridged.

Rising Damp External Walls
Rising damp can affect both internal and external walls. When looking for proof of rising damp on external walls, again you should look out for tide marks. You may even see some of the mortar crumbling between your bricks or stonework and salt deposits too.

Signs of Rising Damp
Rising damp is a relatively rare form of damp and treatment is only going to work should it be appropriately diagnosed. It is therefore vitally important to get a professional diagnosis from a knowledgeable surveyor – this calls for a rising damp survey of your home including analysis of the salts.

It can be hard to distinguish rising damp from other forms of damp like condensation or penetrating damp.

Having said that, the following are a few of the greater common signs of rising damp that you can consider:

Tide marks of salts
Dark patches on walls that can be damp to touch – for a much better indication of rising damp you want to determine that the brickwork / masonry is actually wet and not just the plaster or wallpaper.
Staining of wall coverings, peeling wallpaper & blistering paint.
Damp and musty smell.
Discolouration & fragmenting plaster.
Decaying timber e.g. skirting boards, floor boards, floor joist

Rising Damp Treatment
The most effective and economical way to treat rising damp is to use a damp proofing injection cream. You may choose between complete kits or individual cartridges of cream from leading brands such as Kiesol C and Aida.

The cream is injected or hand-pumped into specially-positioned holes in the mortar course. Once inserted, the damp proofing cream reverts to a liquid. This enables it to penetrate the bricks and achieve complete absorption. Because it cures, it creates a powerful water-repellent barrier and a new chemical DPC that stops water from rising in the wall. For full instructions how to take care of rising damp with damp proofing cream read our guide to injecting damp proof courses.

Alternatively, you can install a fresh damp proof membrane to act as a damp proof course. This is a much bigger and more complicated process that involves taking out each brick along the failed mortar course and installing a new physical damp proof membrane.

How to treat rising damp on internal walls
When you see evidence of rising damp on internal walls, you need to take out any wallpaper and plaster back to the bricks or substrate. You will also have to do this on the external wall of the property.

Check that the DPC has not been bridged at all before proceeding with the injection of a fresh DPC. Treating rising damp on internal walls is centered on carrying out the injection process as outlined above and then entering a situation to make good and redecorate internally.

The quickest way to do this is with a damp proof membrane.