As mentioned earlier, drainage, heating, ventilation and lime plasters are the heritage- or conservation sector's default solution to rising damp. Although these factors are important and necessary, in addressing rising damp they work with variable success. They can give good results in certain buildings while they do very little against rising damp in some others.
These limitations become much more obvious when dealing with very old (e.g. 300-1000 year old) buildings which are often also protected due to their age or historical significance.
In many such buildings rising damp has already been tackled at some point (or multiple times) by a drainage, heating, ventilation and lime mortar combination - yet the crumbling, efflorescence or the overall decay of the building fabric persists. In some cases, in lack of anything better, more drainage and more similar measures are being specified in hope to solve or alleviate the problem.
Based on a large number of observations and specialist measurements on many old buildings, we have identified a number of factors that explain some of the limitations and failures of the drainage-ventilation-lime combination.
When Can Rising Damp Be Managed?
- More recent (not very old) buildings
- Buildings with thinner, not very salty walls
- Lighter cases of rising damp
1. More Recent Buildings
More recent buildings, the ones typically not older than 100-150 years respond better to various renovation solutions than their much older counterparts. A significant part of the UK building stock falls in this category: post- and pre-war buildings, some of the Victorian / late Victorian buildings etc.
2. Thinner, Not Very Salty Walls
Newer buildings with thinner or cavity walls can often be successfully managed by a combination of heating, ventilation and drainage. In contrast, older solid or rubble-infilled walls subject to interstitial (in-depth) condensation represent more complex cases that need a more complex intervention.
3. Lighter Cases of Rising Damp
When the dampness problem is just starting and it is addressed at an early stage, renovation-only solutions can manage the problem satisfactorily. Please be aware that modern building materials can cover-up the problem, making serious problems of rising damp appear insignificant.
When A Dehydration System Is Needed?
The following cases will most likely need a dehydration system to get the rising damp problem permanently solved:
- Very salty walls
- Buildings older than 150-200 years
- Walls thicker than 600 mm
- Cellars / basements with moderate dampness
- When other methods can't be applied
- A long-term permanent solution is needed
1. Very Salty Walls
One of the very interesting observations / discoveries we have made is that salts are the primary driver behind the residual moisture content of the walls. The amount and nature of salts found in the building fabric determines to a large degree:
- Its ongoing moisture content
- The dehydration period, how long it takes the wall fabric to dry out
- The "air-dry" (equilibrium) moisture content of the walls following the dehydration
Generally, the saltier a wall fabric: the higher its moisture content, the longer the dehydration period and the higher its air-dry moisture content will be.
As the amount and nature of salts can only be determined by specialist salts measurements, here are some indicators on how you can assess whether you are dealing with a very salty wall fabric:
- Abundant efflorescence (salts crystallization) on the face of the walls or plaster
- Crumbling or destroyed bricks that easily disintegrate at touch
A very salty wall fabric typically responds poorly to traditional renovation measures. Implementation of drainage will not make a huge difference as the hygroscopic salts will still be pulling in a lot of humidity from the air. Lime plasters will be relatively short lived as the salts will fill up and break down the plaster's pore structure, making them only a temporary, sacrificial solution.
2. Very Old Buildings
Salt crystallization is an additive or cumulative process. Over time rising damp keeps piling up more and more salts in the building fabric, so the older the building fabric gets the saltier it becomes. However the build-up of salts also depends on some other factors such as porosity, abundance of water in the ground etc.
Buildings typically older than 150-200 years often go past that threshold that they can't be satisfactorily dried out by a combination of heating, ventilation or drainage. Even if the surface of the walls appears to be "bone dry" – which is often the case due to modern cement-based plasters that hide the dampness problem, or lime plasters that breath out the humidity from near the surface – the core of the walls is damp.
Re-plastering 300-400 year old walls with lime is often just a temporary affair as the accumulated ground salts will break down the lime within a few years and the walls will need ongoing repair - which is both costly and messy.
3. Thick Walls
Wall thickness is another key variable that significantly determines the moisture content of walls. Think about this: the evaporation surface (e.g. left and right face) of a thin and thick wall is the same, yet they have a significantly different volume. The thicker the wall the higher its volume, the more moisture it can retain.
Based on our observations, walls thicker than 600 mm can be increasingly difficult to be dried out by traditional means. Such walls can be fully dehydrated with our dedicated magnetic DPC system. 1 - 1.5 m thick church walls also respond very well to our solution and they reach air-dry values within 2-3 short years.
4. Cellars or Basements with Moderate Dampness
Solving dampness in basements often requires invasive and costly solutions such as tanking, sump-pump and membrane systems. In many basements that are not very damp or subject to significant sideways pressure, our dehydration system can create enough impact to solve the dampness problem in a less invasive and more cost-effective way.
5. When Other Methods Can't Be Applied
In certain cases traditional renovation options can't be applied due to various environmental constraints (e.g. not possible to add drainage in the city centre; or the removal of cement render is work intensive, costly or damaging to the underlying building fabric).
In these cases our DPC system is your best bet as it can overcome many of these limitations, including the dehydration of non-breathable walls (e.g. with cement render) in the presence of concrete floors, which with traditional means could not be dried out.
6. A Permanent Solution Is Needed
There are just certain cases when - regardless of the nature of the project (e.g. age, size and construction of the building) - a FULL and PERMANENT solution is needed with a long-term outcome in mind. In these cases our dehydration system is the best alternative.