Case Study · Tanking & Penetrating Damp
Tanking a Misdiagnosed Damp Problem in Headington, Oxford
A family whose damp came back just six months after another firm treated it, because it had been misdiagnosed. Here is how we found the real cause and fixed it properly with tanking.
Written by Sam Fitzgerald, Founder & Surveyor
The Problem
A local family in Headington, Oxford had damp patches and plaster damage in their home, and they had already tried to deal with it. Another firm had carried out a damp survey and damp proofing, but the damp was back within six months. They had paid to fix it once and were now looking at the same problem all over again.
The Diagnosis
The reason it returned was simple: it had been misdiagnosed. The original treatment had been carried out for rising damp, but that was not the cause. On inspection we found severe moisture on the internal walls, damaging the plaster, and traced it to porous brickwork combined with a tree growing against the external wall, both driving penetrating damp through from outside.
A rising damp treatment was never going to stop water coming in sideways through the external wall, which is exactly why the problem came straight back.
Our Solution
To protect the interior against the penetrating damp, we installed a cement tanking slurry to the affected internal walls. This creates a strong barrier that holds back the moisture coming through the structure and protects the plaster and internal finishes. With the real cause identified, the treatment matched the problem this time. On completion the work was backed by our written 10-year guarantee.
The Outcome
The damp was stopped, the internal walls and plaster protected, and the family finally had the issue resolved at the cause rather than the symptom. This time the right fix the first time, backed by a 10-year guarantee.
Why It Matters
Misdiagnosis is the single most common reason damp comes back. Rising damp, penetrating damp and condensation can look alike on the wall, but they have completely different causes and need completely different treatments. Treat the wrong one and it returns, often within months, exactly as it did here before we were called in. Getting the diagnosis right first, which is what a proper damp survey is for, is what stops people paying twice.
Frequently Asked Questions
Why has my damp come back after treatment?
Almost always because the original cause was misdiagnosed. If a penetrating or condensation problem is treated as rising damp, or the other way round, the real source is left untouched and the damp returns, sometimes within months.
What is the difference between rising and penetrating damp?
Rising damp comes up from the ground through the base of the walls. Penetrating damp comes in sideways through the walls, often through porous brickwork, defective pointing or water held against the wall by vegetation. They can look similar inside but need different treatments.
What is tanking and when is it used?
Tanking is a waterproof barrier, here a cement tanking slurry, applied to walls to hold back moisture coming through from outside or below. It is used where water is penetrating the structure, as it was in this case.
Can a tree cause damp?
Yes. A tree or heavy planting against an external wall keeps the brickwork wet and can push moisture through to the inside, which was part of the cause here.
Has Your Damp Come Back After Treatment?
If this sounds familiar, the original diagnosis may have been wrong:
A damp survey will find the real cause before any treatment is recommended, so you do not pay to fix it twice.
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