Case Study: Rising Damp Treatment in Horsham
The problem was rising damp on old property in Horsham. Had blistering paint. Once plaster was being removed it was evident that the wrong plaster had been installed in several areas. That was drawing moisture. Plaster was all removed from areas needed. Chemical injection carried out and waterproof plastering carried out.
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Rising Damp in a Horsham Home: Why the Wrong Plaster Was Making Things Worse
Rising damp is one of those problems that rarely announces itself clearly. More often, it creeps up gradually - a patch of peeling paint here, a slight musty smell there until eventually the signs become impossible to ignore. That was precisely the situation at a period property in Horsham, where the owners had been watching their walls deteriorate for some time before calling us in.
What Gavin found when he arrived told a familiar story, but with a complicating factor that explained why the problem had become as serious as it had.
What Is Rising Damp?
Rising damp occurs when groundwater travels upward through the fabric of a wall by capillary action the same process that draws water up through a sponge. All masonry is porous to some degree, and in older properties, the original damp proof course (DPC) the horizontal barrier built into the wall to stop this moisture rising can fail over time, or may be absent altogether.
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As moisture rises through the wall, it carries with it soluble salts from the ground. These salts deposit themselves within the plaster as the water evaporates, causing the characteristic blistering, bubbling, and flaking of paint and plaster that homeowners tend to notice first. Left untreated, rising damp causes ongoing damage to plaster, decorative finishes, and in time, to the structural fabric of the building.
The Problem at This Horsham Property
At this particular property, the telltale signs were visible across several walls: paint blistering and lifting away from the surface, discolouration at low level, and a damp, chalky feel to the plaster underneath. Rising damp was the clear cause, but when Gavin stripped back the affected plaster to assess the walls, a second issue came to light.
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In several areas, the wrong type of plaster had been used, almost certainly applied at some point during previous renovation work. Standard gypsum-based plasters are not suitable for use in situations where moisture is present. Gypsum is hygroscopic, meaning it actively absorbs moisture from its surroundings, and when used on walls that are already subject to rising damp, it draws water further into the wall rather than managing it. This was compounding the original problem significantly, accelerating the damage and making the visible symptoms worse than they might otherwise have been.
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This is a common issue in older properties that have been worked on over the years by various tradespeople, not all of whom will have specialised knowledge of damp.
Patching over a damp problem with standard plaster is rarely effective and can make remediation more complex when it is eventually addressed properly.
Stripping Back and Installing a Chemical Damp Proof Course
With the extent of the damage properly understood, Gavin stripped all the affected plaster back to the bare masonry. This step is essential - there is no point treating the wall or applying new plaster over material that is contaminated with salts and moisture. The wall needs to be clean and fully accessible before any treatment can take place.
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Once the walls were stripped, Gavin carried out a chemical damp proof course injection. This process involves drilling a series of evenly spaced holes along the base of the affected wall, at mortar course level, and injecting a specialist silane-based cream into the masonry. As the cream cures within the wall, it lines the capillary pores in the masonry with a water-repellent coating, creating a new damp proof barrier that prevents moisture from continuing to rise.
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Chemical injection is the standard recommended method for treating rising damp in existing walls and, when carried out correctly by a qualified technician, provides a durable and reliable solution. The holes are neatly filled following treatment, leaving the wall ready for replastering.
Waterproof Plastering to Complete the Work
The final stage was replastering using a waterproof renovating plaster, a specialist material designed specifically for use in damp conditions. Unlike gypsum plaster, waterproof plastering is formulated to tolerate residual moisture in the wall and to manage the hygroscopic salts left behind by rising damp. It contains pore-blocking additives that prevent salt migration to the surface, and its dense, water-resistant composition means it will not absorb moisture the way standard plaster does.
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Gavin applied the renovating plaster in the correct specification across all the treated areas, building it up in the appropriate coats and finishing it to a smooth surface ready for decoration. Once fully cured, the walls were stable, dry, and properly protected both from the existing salt contamination and from any future moisture movement.
Getting Rising Damp Right, First Time
This job in Horsham is a good illustration of why proper diagnosis matters as much as the treatment itself. The damp proof course injection alone would not have resolved the problem had the unsuitable plaster been left in place. And applying new plaster without treating the damp first would simply have produced the same damage all over again. Each step stripping, treating, and replastering with the right material is necessary, and each one depends on the one before.
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Gavin Jones is a City and Guilds qualified plasterer with over 25 years of experience, and a PCA Qualified Technician for damp proofing, with the expertise to diagnose and treat rising damp correctly across all types of property.
Based in Sussex, he carries out rising damp surveys, chemical damp proof course treatments, and specialist replastering work in Horsham and throughout the surrounding areas of Sussex and Surrey.
If you have noticed signs of rising damp in your home - blistering paint, tide marks, or damp plaster at low level, get in touch for a survey and quotation.
We are members of Checkatrade and are committed to straightforward, honest advice and quality workmanship.