Damp patches caused by failed pointing
A damp patch on an internal wall that appears after heavy rain is one of the clearest signs that water is getting through from outside. The difficulty is that the same symptom can have very different causes - and the wrong treatment will either waste your money or make things worse.
This page focuses on damp caused by failed mortar joints, which is among the most common causes we deal with across Yorkshire, particularly on older solid-wall properties.
How to tell if your damp is caused by failed pointing
Before spending money on any treatment, it helps to understand which type of damp you're dealing with. There are three main types, and they present differently.
Penetrating damp from failed pointing
This type appears on external walls, often on upper floors or on exposed elevations. The critical indicator is that it gets noticeably worse after rain and tends to improve during dry spells. It usually appears as a defined patch rather than a broad or rising stain. On a solid stone or brick wall with no cavity, it can come through anywhere the pointing has failed. On a property with a cavity wall, it can still occur if the outer leaf is heavily saturated.
Rising damp
This appears at the base of walls, typically up to about a metre high, and tends to have a tidemark (a horizontal stain line where salts deposit as moisture evaporates). It does not correlate closely with rainfall events. Rising damp is far less common than is often suggested, and in many cases what is labelled as rising damp is actually penetrating damp from a different source.
Condensation
Condensation appears on cold surfaces, typically in corners, behind furniture, or around cold bridges like window reveals. It does not appear directly after rain - it tends to be worst in the morning, overnight, or when ventilation is poor. Condensation does not respond to external repairs.
If your damp patches appear after rain, appear on external-facing walls, and reduce during dry weather, failed pointing is the most likely external cause.
What damp from failed pointing looks like at different stages
Early stage: A slightly darker patch on the plaster, perhaps 20–40cm across, that appears after rain and fades over the following days. At this stage the damage is limited and repair is straightforward.
Intermediate stage: The patch is larger, takes longer to dry out, and paint may begin to bubble or flake. Salts from the masonry can start to deposit on the surface (efflorescence), leaving white powdery marks. Plaster may begin to sound hollow when tapped.
Advanced stage: The patch is present for most of the autumn and winter, plaster is blown (hollow and detached from the wall behind), mould may be visible, and timber elements nearby - skirting boards, window boards, floor joists if relevant - may have been affected. At this point, internal remediation will be needed once the external cause is addressed.
What to do - and what not to do
Don't paint over it. Applying fresh emulsion, masonry paint, or a tanking slurry to an internal wall does not address the external cause. Water will continue to enter through the pointing, the patch will reappear, and any decorative finish applied over active damp will fail quickly.
Don't apply internal damp-proof treatments as a first response. Internal waterproofing products are designed for specific situations - basement tanking, for example. Applied to a wall that is wet because of external pointing failure, they trap moisture rather than stopping ingress, and can cause further damage to plaster and masonry.
Do address the external cause first. Repointing the affected elevation stops new water entering. Once the wall is dry, internal redecoration can follow and will last.
Seasonal patterns and timing
Damp from failed pointing is almost always worse in autumn and winter. Rainfall is higher, temperatures are lower, and walls have less opportunity to dry out between weather events. Properties in exposed positions - particularly in areas like Ilkley, Otley, and on the higher ground around Skipton - can see rapid saturation of the outer leaf during persistent southerly or westerly rain.
Walls that appear fine in a dry summer can present significant damp problems by November. This is not a sign that the problem has suddenly appeared - it has usually been developing gradually, and the summer just didn't expose it.
How long does a wall take to dry out after repointing?
This depends on how saturated the wall is, the construction type, and the weather conditions after repair. A moderately affected solid brick wall can take four to eight weeks to fully dry in normal autumn conditions. A heavily saturated stone wall can take longer. We'll give you an honest expectation when we assess the job.
Internal redecoration should wait until the wall is confirmed dry. Replastering before the wall is dry is one of the most common reasons damp-related repairs fail again - the new plaster simply blows off.
How we address it
We carry out a full assessment of the affected elevation to establish where mortar has failed and to what depth. Depending on the building type and age, we then carry out cement mortar repointing or lime mortar repointing to restore the wall's weather resistance. On some properties, a breathable water-repellent treatment applied after repointing provides additional protection for the masonry itself.
If you're not certain whether the pointing is the cause, or if damp is appearing in several locations, a Building Leak & Damp Inspection will identify all active defects before we recommend any repair work.
Frequently asked questions
Q1. Should I replaster internally before sorting the pointing? No - internal replastering before fixing the external cause is wasted effort. If failed pointing is allowing rain into the wall, new plaster will simply get damp again once it rains. Fix the external cause first. Once Northern Seal & Joint has repointed the wall and the masonry has fully dried out, any internal finishing work can be done properly and will stay sound long-term. Q2. Will the damp patches disappear after repointing? Yes, but it takes time. Once the external water entry is stopped, the wall needs to dry out fully before internal patches fade. Depending on how long the wall has been saturated and how thick the masonry is, this can take several weeks to a few months. Yorkshire stone walls in particular hold moisture for longer than cavity-wall construction. Do not redecorate internally until you are confident the wall has dried thoroughly. Q3. How can I tell if the damp is caused by failed pointing rather than rising damp? The timing is the clearest indicator. If damp patches appear or worsen after rainfall and improve in dry weather, penetrating damp from failed pointing is the likely cause. Rising damp tends to be persistent, appears at low level near the floor, and is unaffected by rain events. A tide mark or salt staining on the wall can indicate rising damp. If you are unsure, Northern Seal & Joint can carry out a building inspection to identify the source. Q4. Can I paint over damp patches once the repointing is done? Not straight away. Painting over damp masonry or plaster seals moisture in and usually results in bubbling and peeling. Wait until the wall has dried completely, then use a breathable paint or masonry coating rather than a non-breathable product. Solid walls, including those common in older Bradford and Yorkshire properties, need to be able to release moisture vapour. Using the wrong paint can extend the drying time and cause further damage to the plaster surface. Q5. What is the difference between breathable and non-breathable plaster, and does it matter? It matters considerably for older solid-wall properties. Non-breathable (cement-based) plaster applied to a wall that needs to release moisture will trap water behind it, causing the plaster to blow and the wall to stay damp. Breathable plasters - typically lime or specialist renovation products - allow moisture to move through and evaporate, which is how older buildings manage moisture naturally. For any property with solid masonry walls, the correct internal finish is just as important as the external repair. Q6. How much does repointing typically cost if the cause is failed pointing? Repointing costs vary depending on the extent of the area, accessibility and the type of mortar required. As a rough guide, cement repointing in Yorkshire typically runs from around £30–£60 per square metre, though jobs on scaffolded elevations or requiring lime mortar will cost more. Northern Seal & Joint provides itemised quotes once we have inspected the property. Getting the right diagnosis first prevents paying for work that does not address the actual cause.
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