How to Fix Damp - Part 1

Updated: Oct 14, 2021

So, you’ve been told you have rising damp? Or, you’ve got damp at low level on the ground floor? Maybe you’ve had a damp proofing company offer you a free survey and diagnosed rising damp using a damp meter? We recently conducted an in depth building survey at a property in Leeds which included a full inspection of the cause and extent of damp, as well as the remedy for it.

If you’ve been told that you have rising damp, or you have the typical symptoms. Speak to us, we will find the correct causes and specify the correct repairs. The Survey Instruction

Recently we conducted a full building survey on a property in Leeds. The property is suffering from a major damp problem to all rooms. To the untrained eye, this property could easily be diagnosed with a rising damp problem and the wrong repairs carried out at an unnecessarily high cost.

The Survey Process

Firstly, we scoped out the property to understand what the damp symptoms were and what our client would like to achieve, as well as what their budget was.

We then moved on to establish the extent of the dampness. We surveyed the roof space, each individual room, and below the floor boards. It was established that the property had the following defects.

Damp, crumbling plaster to every room up to 1m high.
Damp, mouldy lathe and plaster ceilings
Damp, crumbling plaster to chimney breasts
Damp, rotten floorboards in some rooms including slight evidence of woodworm
Damp to the ground floor joists

This blog is specifically referring to the rising damp symptoms at the property and a follow up blog will explain regarding the penetrating damp to the first floor and how damp can cause structural problems to timber floors.

Now that we understand the symptoms that our client is experiencing, and we had established the extent of the dampness, we moved on to establishing the cause.

The Cause

Before attending the property, we already had a good idea of what the causes were because in reality, damp is very simple.

Moisture enters a building through penetration, rising from the ground, or from the air. Damp is usually a combination of these and knowing the typical signs and where to look is our speciality.

Cause 1 - Rising Damp

This is the process whereby ground water enters a property by rising through the building fabric by capillary action resulting in damp internally.

It is not always possible to diagnose rising damp as there are many other issues that can simulate the typical signs of it.

In this particular instance, on the face of it, it may have been easy to suspect rising damp.

Typical symptoms of rising damp - damp up to the red line

However, during our investigations we identified that this is not true rising damp where the damp proof course has failed. Carry on to see our diagnosis.

Cause 2 - Penetrating Damp (Lateral Penetration)

As part of our investigation we identified that the tarmac path around the property has been raised. This path has been raised so that it is above the damp proof course.

Let’s take a step back and explain what a damp proof course is. This is a physical barrier built into the walls at the time of construction to stop ground water rising into the property.

In order for the damp proof course to be effective, the external ground levels should be a minimum of 150mm below it to prevent rainwater splashing above it.

Additionally, the damp proof course should not be bridged. This is where something, either cement, render, or any other physical object is covering the damp course and allows moisture to bypass it.

At this property, we established that the ground levels were above the damp proof course. This was allowing rainwater and groundwater to penetrate the walls above the damp proof course.

Damp proof course bridged along this line

Our recommendations here are for the ground levels to be excavated to at least 150mm below the damp proof course.

Cause 3 - Bridged Cavity

During the inspection we drilled a series of holes in the external wall to inspect the cavity with a borescope camera.

We established that the cavity had been bridged by debris and mortar, likely at the time of construction.

Even though the debris has been bridging the cavity for many, many years, this did not create a problem until the external ground levels were raised. However, as this is cavity construction, the debris in the cavity was creating a bridge for moisture from the external wall, to the internal wall, causing dampness at low level, mimicking rising damp.

Following this, our recommendations are that the cavities are opened and cleared of all debris.

Cause 4 - Hygroscopic Salt Contamination

As the property has been suffering from damp for a prolonged period of time, as the moisture has migrated to the inside wall, some salts present within the brickwork have dissolved into the moisture.

As the moisture soaks through the plaster and begins to evaporate, it leaves the salts behind causing contamination in the plaster.

Furthermore, this property has been vacant for a prolonged period and had no working heating. Because of this, the property was cold with very little ventilation. These issues have combined to make the perfect circumstances for condensation to occur and, as the salts are hygroscopic, they absorb this surface moisture, making the damp problem worse.

It is vital, that the salt contaminated plaster is removed and the walls allowed to dry properly before replastering. If walls are replastered too soon, salt contamination will continue to occur and the damp will periodically reappear.

Repairs