Here are some (common) solutions for the handling of rising damp - both traditional and modern approaches. Some of them are partial solutions to rising damp (e.g. they don't address all critical aspects of rising damp) or they are just plain incorrect for certain applications - e.g. not suitable for listed or heritage buildings because they are either too invasive, non-breathable or their application would long-term damage the building fabric.
The efficiency or inefficiency of these solutions can be easily evaluated in light of three very important concepts:
- Rising damp is a STANDALONE phenomenon that can occur on its own.
- Rising damp is NOT CAUSED by various building defects - e.g. bridged ">damp proof course, the use of cement plasters, lack of heating etc.) – although such problems, by creating their own set of dampness issues, interfere with the dynamics of rising damp. Fixing them brings about an overall improvement, but rising damp, as an underlying condition, will create new problems (years) later.
- Solving rising damp long-term is always a two-step process, involving:
- Step 1: The installation of a damp proof course - to "cut off" the building from the water table
- Step 2: Renovations - to make damages good, while also handling the problem of ground salts
Traditional / Building Friendly Solutions
Lime is preferred for the replastering of old buildings as it offers the following important benefits:
- Breathable: it lets moisture freely evaporate out from the underlying (damp) wall fabric, preventing the excessive build-up of humidity.
- Porous: it stores in its pore structure the crystallizing salts, giving a dry, salt-free surface.
- Flexible: it does not crack. It can also self-heal small cracks.
THE PROBLEM: despite of the above benefits, lime plastering alone is one of the partial solutions to rising damp as the rise of water and salts continues in the background. Once salts fill up the pores of lime, it starts crumbling and the walls need to be replastered.
Lime can control rising damp temporarily in an elegant, building-friendly way, keeping surfaces dry and presentable but it is not a solution to rising damp long-term.
MISSING: for a long-lasting solution, lime plastering should be used in conjunction with a damp proof course (e.g. a non-invasive magnetic DPC suitable for all listed buildings), and a salt-resistant base coat under the main plaster coat.
Lime plaster ruined by salts in less than a year
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THE PROBLEM it is a misconception that drainage can drain away ALL water from the base of the walls. Not all moisture is drainable. Just think of a well wrung clothing: it still contains a lot of undrainable moisture in the fabric that can only be driven out by evaporation.
Lab test have shown that walls in permanent contact with a well drained soil can still absorb and accumulate a significant amount of moisture, enough to create rising damp. In fact, this is the natural development cycle of rising damp.
MISSING: without a damp prof course rising damp is still present in the background and will be creating problems.
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Heating and ventilation facilitate evaporation, but in the presence of rising damp they also have a secondary, undesirable effect.
THE PROBLEM: in lack of a damp proof course, the bottom of the wall is connected to the water table (unlimited water supply). Evaporation creates a pressure difference which draws up more moisture and salts from the ground, creating an ongoing water intake from the ground into the walls. You can't dry out a masonry with unlimited water supply at its base.
MISSING: a damp proof course is needed to detach the masonry from the water table.
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The combined effect of lime plastering, drainage and heating & ventilation creates a better impact onto the building than having only one or two of these individual actions done, but they still represent partial solutions to rising damp.
THE PROBLEM: experience has shown many times, that although these combined actions help to slow down rising damp and can buy few years of apparent rising-damp-free-years, the problem will eventually return. These actions are not a permanent fix as they won't substitute the role of a damp proof course.
MISSING: the addition of a damp proof course is necessary for a permanent fix.
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Modern Solutions
Replastering with a modern cement plaster or special renovation plaster is a common way of replastering old buildings after rising damp.
Tanking is the application of some waterproofing material onto the surface of the affected damp walls in order to block dampness and salts, and to keep wall surfaces dry. Most common waterproofing materials are: cement plasters or slurries, bituminous coats, plastic membranes or special non-breathable cement-based “renovating” plasters, often with waterproofing or salt-blocking additives.
THE PROBLEM: all of the above solutions using modern waterproofing materials are non-breathable, resulting in the accumulation of moisture behind the waterproofing barrier, often rising higher in the background. This invisible dampness accumulation long-term results in an increasingly damp and damaged building fabric.
MISSING: a damp proof course must be part of the overall solution. A magnetic DPC can dry out non-breathable walls already tanked or covered with membranes etc. Tanking should not be part of any rising damp solution as better alternatives exist.
Waterproof membranes on old walls accumulate moisture under the surface
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Skimming is a “corner-cutting” plastering solution, by applying a thin fresh coat of plaster on top of the old one, without solving the underlying rising damp, which should include the complete removal of old, salty plaster.
THE PROBLEM: the old plaster is often very salty. The water from the fresh plaster moves these salts into the fresh plaster, resulting in its breakdown due to salt crystallization within a short few months. Thus skimming should be avoided at all costs as it can be a costly mistake long-term.
MISSING: a damp proof course must be part of any long-term rising damp solution. The old, salty plaster needs to be completely removed and replaced with fresh plaster with a salt-resistant base coat.
Skimmed wall surface ruined by salts only 6 months later
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Dot and dabbing is a “budget” plasterboard mounting technique that involves the gluing of the plasterboard onto the old (often salty or damp) wall surfaces.
THE PROBLEM: salts can easily migrate into the plasterboard through the plasterboarding glue, resulting in damp patches on the surface. In addition, thermal bridging through the plasterboard glue can create condensation patches, especially in case of solid walls due to cooling.
Plasterboarding the proper way, by mounting the plasterboard on timber or galvanized steel battens creates a long-lasting solution, but without a damp proof course to stop the rise of water, plasterboarding just hides the problem.
MISSING: for a permanent remedy of rising damp, a damp proof course needs to be installed. If the wall is crumbling, the salty plaster also needs to be replaced before putting fresh plasterboard mounted on battens.
Dot and dab plasterboarding can result in damp patches in old walls
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Waterproofing paints are a short-term quick-fix to hide starting rising damp problems.
THE PROBLEM: over-painting affected areas won't last, they need to be repainted every few months as the underlying salts will destroy the paint and the plaster.
MISSING: to solve rising damp, a damp proof course needs to be installed. The peeling paint indicates salts in the plaster, which also needs to be replaced eventually for a permanent fix.
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Various wall-ventilation systems have been available since the 1980s. The Schrijver System from the Netherlands is probably the most known such system.
The embedded ventilation blocks sticking out of the wall fabric act as small wind channels, catching some of the winds that create extra evaporation in the depth of the wall,
THE PROBLEM: in lack of a damp proof course, the bottom of the wall is connected to the water table (unlimited water supply). Evaporation creates a pressure difference which draws up more moisture and salts from the ground, resulting in faster crumbling. Cooling the wall surface also opens the door to potential condensation problems, especially if the internal walls are plastered with modern, cement plaster.
MISSING: a damp proof course to detach the masonry from the water table.
Schrijver system - a wall base ventilation system
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Apparent Workability
The existence and severity of rising damp depends on the balance of water intake vs. water outflow. Doing certain things on the building that reduces or limits the water intake, or improves the water outflow (e.g. via evaporation) results in an overall improvement of the building.
When to Expect Improvement?
As a guideline, here are some cases when some of the above partial solutions to rising damp are likely to result in a decent improvement in the building without the installation of a DPC, despite that rising damp continues to exist in the background.
- Not very old buildings: buildings not older than 100 years respond better to various renovation solutions than their much older counterparts. A significant part of the UK building stock falls into this (late Victorian or newer) category.
- Buildings with thinner walls: rising damp in buildings with thinner 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.
- Lighter cases of rising damp: when the rising damp problem is at an early stage with less salts present, renovation-only solutions can often manage the problem satisfactorily.
When there is Little or No Improvement?
On the other hand, in other buildings, the exact partial solutions to rising damp are going to make much less or no difference. Such cases include:
- Older buildings: buildings typically older than 150-200 years often are 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.
- Thick walls: wall thickness is another key variable that significantly determines the moisture content of old walls. Based on our observations, walls thicker than 600 mm can be increasingly difficult to be dried out by traditional means.
- (Very) Salty walls: a very salty wall fabric 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 quickly fill up and break down the plaster's pore structure, making them only a temporary, sacrificial solution.
Monitoring the moisture content of the fabric with drilled core measurements is a true indicator on how damp a wall is and how well a rising damp remedy solution has worked.