Rising Damp - What Causes It and How Do You Treat It?
Peeling paint at the bottom of a wall, crumbling plaster and white, powdery deposits that keep returning are all common signs of a moisture problem. In many South African homes and buildings, the culprit may be rising damp.
The temptation is often to scrape, patch and repaint. The wall looks good again for a while, but if the source of the moisture hasn’t been dealt with, the problem can return. That’s because rising damp isn’t really a paint problem; it’s a waterproofing problem within the wall itself.
Understanding where the moisture is coming from, what the wall is made from and how the building was waterproofed is therefore the first step towards finding the right solution.
Peeling paint at the bottom of a wall, crumbling plaster and white, powdery deposits that keep returning are all common signs of a moisture problem. In many South African homes and buildings, the culprit may be rising damp.
The temptation is often to scrape, patch and repaint. The wall looks good again for a while, but if the source of the moisture hasn’t been dealt with, the problem can return. That’s because rising damp isn’t really a paint problem; it’s a waterproofing problem within the wall itself.
Understanding where the moisture is coming from, what the wall is made from and how the building was waterproofed is therefore the first step towards finding the right solution.
What exactly is rising damp?
Brick, mortar, plaster and concrete may appear solid, but they are naturally porous. Within these materials are tiny interconnected pores and capillary pathways through which moisture can travel.
In a correctly constructed building, a damp-proof course (DPC) creates a barrier between moisture in the ground and the walls above. If this DPC is missing, incorrectly installed or has failed, moisture can move upwards through the masonry. This is what we refer to as rising damp.
Brick, mortar, plaster and concrete may appear solid, but they are naturally porous. Within these materials are tiny interconnected pores and capillary pathways through which moisture can travel.
In a correctly constructed building, a damp-proof course (DPC) creates a barrier between moisture in the ground and the walls above. If this DPC is missing, incorrectly installed or has failed, moisture can move upwards through the masonry. This is what we refer to as rising damp.
DPC in the wall should overlap the DPM beneath on the side of the floor slab to create a continuous barrier against ground moisture.
A damp-proof membrane (DPM) beneath the floor slab also plays an important role in preventing ground moisture from entering the building. The DPC in the wall and DPM beneath the slab should overlap, creating a continuous barrier against moisture. If there is a break between the two, moisture may be able to bypass the damp-proofing system and enter the structure.
Rising damp typically presents itself on the lower portion of a wall, often within the first metre above ground or floor level. Bubbling or peeling paint, darker damp patches, soft or crumbling plaster and white powdery deposits, known as efflorescence, can all indicate a moisture problem. Another tell-tale sign may be a wall that has been repaired and repainted, only for the same problem to return.
The height of rising damp can vary depending on the construction, porosity of the materials and surrounding conditions, so one metre should not be considered an absolute limit. However, if damp is appearing significantly higher up a wall or in isolated areas, it is particularly important to investigate other possible sources of moisture.
Not every damp wall is caused by rising damp. Leaking pipes, rain penetration, failed exterior waterproofing, poor drainage or lateral moisture ingress can produce similar symptoms, so establishing the source of the moisture is important before deciding how to treat it.
Lateral moisture ingress can occur where the soil level on the opposite side of a wall is higher than the finished ground level of the property, allowing moisture to move horizontally through the wall rather than upwards from below. This is particularly relevant to retaining walls, basements and other partially below-ground structures.
Why repainting isn’t enough
Paint and decorative coatings are the final finish, not the primary waterproofing. If moisture is still moving through the wall, simply scraping off the damaged material and applying another coat of paint may only hide the problem temporarily.
Over time, the continued movement of moisture can result in bubbling, staining, efflorescence, delamination and deterioration of the plaster or decorative finish. The aim should therefore be to deal with the source and movement of moisture first, and repair the finish afterwards.
Treat the moisture first. Finish the wall afterwards.
Paint and decorative coatings are the final finish, not the primary waterproofing. If moisture is still moving through the wall, simply scraping off the damaged material and applying another coat of paint may only hide the problem temporarily.
Over time, the continued movement of moisture can result in bubbling, staining, efflorescence, delamination and deterioration of the plaster or decorative finish. The aim should therefore be to deal with the source and movement of moisture first, and repair the finish afterwards.
Treat the moisture first. Finish the wall afterwards.
How can rising damp be treated?
There isn’t one Cemcrete product that should automatically be used on every damp wall. The correct treatment depends on what the wall is made from, where the moisture is coming from and what finish needs to be applied afterwards.
Where rising damp is moving through brickwork because the original damp-proof course is no longer performing effectively, Cemcrete’s SiliconSeal Solvent-Based Sealer can be used as a remedial damp-proofing treatment. It is a colourless, deep-penetrating treatment that greatly reduces water absorption while allowing the substrate to remain breathable.
How can rising damp be treated?
There isn’t one Cemcrete product that should automatically be used on every damp wall. The correct treatment depends on what the wall is made from, where the moisture is coming from and what finish needs to be applied afterwards.
Where rising damp is moving through brickwork because the original damp-proof course is no longer performing effectively, Cemcrete’s SiliconSeal Solvent-Based Sealer can be used as a remedial damp-proofing treatment. It is a colourless, deep-penetrating treatment that greatly reduces water absorption while allowing the substrate to remain breathable.
SiliconSeal Solvent-Based Sealer can be gravity-fed into brickwork to repair a failed damp-proof course and help prevent rising damp.
For this application, holes are drilled into a single course of bricks at DPC level. SiliconSeal Solvent-Based Sealer is then introduced into the brickwork by gravity feed or pressure injection until the bricks are saturated, creating a remedial damp-proof course. The wall can then be repaired or refinished according to the specified system.
Where moisture is moving through concrete or another cementitious substrate, Permastop offers a different approach. Permastop is a crystalline waterproofing treatment applied as a cementitious slurry to a damp cement surface. Its active chemicals react with moisture to form non-soluble crystals within the pores, capillary tracts and static cracks of the concrete, blocking the pathways through which water would otherwise travel.
Rather than simply creating a waterproof film over the surface, Permastop waterproofs the cementitious substrate from within. Once the crystalline reaction has taken place, Permastop remains dormant within the concrete and can reactivate when moisture returns. This allows further crystals to form within newly exposed capillaries and static hairline cracks, helping to close these pathways and prevent further water movement. It can resist hydrostatic pressure from both the positive and negative side, can be applied to moist surfaces and remains waterproof while allowing vapour transmission. It is suitable for applications including walls with failed DPCs, foundations, concrete slabs and underground structures.
Close-up section of Permastop’s crystalline waterproofing action.
Permastop can also be specified in situations where adjoining soil levels are higher than the finished ground level of the property and moisture is entering laterally through a cementitious wall. Because it can withstand hydrostatic pressure from both the positive and negative side, it can be particularly useful where waterproofing needs to be applied from the inside of a structure because the moisture source is not easily accessible.
One important consideration is that Permastop needs to be in direct contact with cement or concrete to work. It does not react directly with clay bricks unless they are covered with a suitable cement plaster. Where the wall is replastered afterwards, the Permastop system recommends incorporating Cemcrete Water-Repellent Cement into the new plaster.
For walls requiring a flexible waterproofing layer, MatFlex provides another option. This two-component, polymer-modified cement-based waterproofing system adheres directly to concrete, brick and plastered surfaces and is specifically suitable for treating walls affected by rising damp. It is effective under both positive and negative water pressure and can bridge static hairline cracks of up to 0.3mm.
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Once cured, MatFlex can be painted with a high-quality acrylic PVA, tiled over, or left exposed and sealed with a film-forming sealer. However, Cemcrete’s cement-based decorative coatings cannot be applied over MatFlex, so the intended final finish needs to be considered when selecting the waterproofing system.
What about new construction or replastering?
The best time to deal with rising damp is before it becomes a problem. Correct waterproofing and damp-proofing during construction remain important, including ensuring that the DPC and DPM are correctly installed and overlap to create a continuous moisture barrier. Moisture resistance can also be incorporated into cement mortar, plaster and concrete.
Cemcrete Water-Repellent Cement is used in place of ordinary Portland cement and helps reduce capillary absorption, moisture movement, efflorescence and moisture penetration. When used in mortar, it can help reduce rising damp in brickwork.
The best time to deal with rising damp is before it becomes a problem. Correct waterproofing and damp-proofing during construction remain important, including ensuring that the DPC and DPM are correctly installed and overlap to create a continuous moisture barrier. Moisture resistance can also be incorporated into cement mortar, plaster and concrete.
Cemcrete Water-Repellent Cement is used in place of ordinary Portland cement and helps reduce capillary absorption, moisture movement, efflorescence and moisture penetration. When used in mortar, it can help reduce rising damp in brickwork.
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Cement Waterproofing Compound provides a similar function but is added to ordinary Portland cement. It helps reduce capillary absorption of moisture in mortar, plaster and concrete and can also help reduce rising damp in brickwork when incorporated into the mortar.
These products can also form part of the repair process where new plaster or cementitious work is required after the underlying damp problem has been treated.
Cement Waterproofing Compound provides a similar function but is added to ordinary Portland cement. It helps reduce capillary absorption of moisture in mortar, plaster and concrete and can also help reduce rising damp in brickwork when incorporated into the mortar.
These products can also form part of the repair process where new plaster or cementitious work is required after the underlying damp problem has been treated.
Treat the cause, not just the damp patch
A damp wall may look like a fairly straightforward problem, but what is happening beneath the surface can be very different from one building to the next. A brick wall with a failed damp-proof course requires a different approach to moisture moving through a concrete basement wall, and the waterproofing system chosen can also determine what finishes may be applied afterwards.
That fresh coat of paint might hide the problem for a while, but if moisture is still travelling through the structure, chances are you’ll see that damp patch again.
The key is establishing where the moisture is coming from and what the wall is made of before deciding how to treat it.
When in doubt, rather ask before you apply. Contact the Cemcrete team with information and photographs of the affected area, and we’ll help guide you towards the most suitable waterproofing system for your project.
A damp wall may look like a fairly straightforward problem, but what is happening beneath the surface can be very different from one building to the next. A brick wall with a failed damp-proof course requires a different approach to moisture moving through a concrete basement wall, and the waterproofing system chosen can also determine what finishes may be applied afterwards.
That fresh coat of paint might hide the problem for a while, but if moisture is still travelling through the structure, chances are you’ll see that damp patch again.
The key is establishing where the moisture is coming from and what the wall is made of before deciding how to treat it.
When in doubt, rather ask before you apply. Contact the Cemcrete team with information and photographs of the affected area, and we’ll help guide you towards the most suitable waterproofing system for your project.
