Rising Damp Treatment to a Sitting Room, High Wycombe HP13
A French drain that had just been installed looked like the obvious answer, but it turned out the real story was hiding in the wall itself. Here’s how the survey got to the bottom of a slowly spreading damp patch in this High Wycombe sitting room.
Project at a Glance
The Brief
The client asked us out to her detached home on Amersham Hill Drive after noticing damp patches slowly spreading in the sitting room. A French drain had recently been installed around the property, and she wanted to know whether that was somehow behind it or if something else internal was going on. Our surveyor, Lionel Sewell, went out to take a proper look, checking the external elevations, the drainage that had just been installed, and the affected wall inside using moisture readings.
It’s a fair question to ask when you’ve just paid for drainage work, and the damp hasn’t gone away. The answer here turned out to be that the French drain was actually doing exactly what it should.
What the Survey Found
Outside, everything pointed to a well-cared-for property with one or two things worth tidying up. There was a visible slate damp-proof course sitting at the correct height above ground level, and the French drain that had recently been installed by others, along with ground levels sitting below the DPC, were genuinely good preventative measures, helping divert water away from the foundations and reduce hydrostatic pressure. There was no doubt about the fact that there were many leaves trapped inside the gutter, which led to the overflowing of the gutter, resulting in water spilling out to the ground outside the door of the sitting room.
In the interior of the property, the signs of mould formation were present on the right side of the garden-facing wall of the sitting room. At first glance, there seemed to be an issue of leakage from the nearby radiator, which was recently checked and repaired, but when Lionel took the measurements of moisture content throughout the wall, the picture changed, and the readings of moisture content were found to be high throughout the wall and not only near the radiator.
The Slate DPCs used in this kind of building are quite common and have a very long life span, but they can crack, delaminate, or become bridged with material inside the cavity over time. After that, the moisture content bypasses the entire barrier and results in rising dampness. That’s what the readings here were pointing to; no odours and no penetrating damp were found, but rising damp was confirmed along both the garden-facing wall and the right side wall.
The Treatment Plan
We specified a With rising damp confirmed rather than a drainage or leak issue, the plan was a full damp-proofing treatment to the affected walls, covering 6.5 sq.m as marked on the surveyor’s floor plan.
The existing skirting boards would be carefully removed, followed by the render, taken back to a set height to expose the bare masonry and clear out any contaminated material. From there, holes would be drilled into the pointing at set intervals and injected with Dryzone damp-proofing cream, which spreads through the brickwork to form a new, durable damp-proof course. The walls would then be finished with two coats of a specialist waterproof render containing salt inhibitors, followed by a final skim coat ready for redecoration, all backed by a 20-year guarantee.
A few things needed doing around the edges of the job. The radiator on the affected wall would need removing and refitting by a plumber before and after the works, and redecoration, including replacing the skirting boards, would need to wait 5–6 weeks after completion to let the treatment cure properly, using a breathable paint once it was ready. The Client was also advised that anyone drilling into the treated walls afterwards, plumber or decorator, should fill the holes with silicone before inserting wall plugs, to avoid compromising the new barrier. Alongside the internal works, clearing the gutters and downpipes and removing moss from the roof were flagged as sensible maintenance to keep external moisture away from the walls going forward.
The Work Carried Out
Carl Shoreman was on site for 2 days to carry out the treatment: hacking off the affected render, injecting the new DPC, and re-rendering and setting the wall ready for redecoration. No unexpected issues came up, and the job stayed within the agreed scope.
The Result
The job was completed on 3rd February 2026. The customer was present at completion and walked around the property to see the finished work, confirming it matched what had been agreed and that the work area had been left safe and tidy. The job was signed off on site and later approved by our Head Contractor.
Worth noting from this one: a new French drain and good ground levels don’t rule out rising damp on their own. The two problems can sit side by side, and treating just the drainage while leaving a compromised DPC untouched would have left the patch creeping back regardless.
Rising Damp FAQs
Can rising damp happen even with a good French drain?
Yes. A French drain manages surface and groundwater around the foundation, but it doesn’t repair a damaged or bridged damp-proof course. If moisture is bypassing the DPC within the wall itself, drainage improvements outside won’t stop it.
What is a Dryzone DPC injection?
Dryzone is a damp-proofing cream injected into holes drilled along the base of an affected wall. It spreads through the surrounding masonry and cures to form a water-repellent barrier, effectively creating a new damp-proof course.
Why does the treated wall need to cure for 5–6 weeks before redecorating?
The new DPC and waterproof render need time to fully cure and allow residual salts and moisture in the masonry to come through safely. Redecorating too soon risks trapping moisture behind the new finish.
How can I tell if damp is coming from a failed DPC rather than a leak?
A leak tends to show up as a localised, often patchy, reading around one spot, whereas a failed or bridged DPC typically produces consistently high moisture readings along the base of the whole wall. A moisture meter survey is the reliable way to tell the two apart.
Do you cover High Wycombe and Buckinghamshire for damp surveys?
Yes, we carry out damp surveys and rising damp treatment across High Wycombe, Buckinghamshire and the surrounding areas.
Noticed a damp patch that keeps creeping back?
Our qualified surveyors diagnose the real cause and give you a fixed-price quote. The survey fee is deducted from the cost of work if you go ahead.
Survey carried out by Michael Young, waterproofing surveyor at Advanced Damp. Project completed in Fulham, SW6.
Sam Fitzgerald is the founder of Advanced Damp and a working damp and structural waterproofing surveyor with over 12 years of experience diagnosing and treating moisture problems in residential and commercial properties across London and the South East. He is FODCS certified (a Federation of Damp Certified Surveyor) and a member of the Federation of Damp. His hands-on work covers rising damp, penetrating damp, condensation, basement waterproofing to BS 8102, and thermal imaging surveys, and he has personally completed over 400 damp surveys across properties of every type and age. Everything he writes draws directly from jobs he has carried out. He does not write about treatments, products or causes he has not dealt with first-hand in the field.
