The damp-proofing industry in the UK is, frankly, full of bad advice, unnecessary treatments and eye-watering bills for work that either doesn't address the real problem or — in some cases — actually makes it worse.
As RICS-accredited surveyors who regularly inspect properties that have been through the damp-proofing mill, we see the consequences every week. Here are five of the most damaging myths, exposed.
Myth 1: "If There's Damp, You Need a Chemical Injection DPC"
This is the biggest myth in the industry and the one that costs homeowners the most money. A chemical injection damp-proof course involves drilling holes along the base of the wall and injecting a chemical compound that's supposed to form a barrier against rising damp. It costs typically £2,000–£8,000 or more.
The problem is that chemical injection DPCs are often prescribed when rising damp either isn't the cause of the problem at all, or when a much simpler and cheaper solution exists. Many Victorian properties with damp at the base of their walls simply have a bridged or damaged original damp-proof course — often because external ground levels have been raised. Lowering the ground level can cost £200 and solve the problem completely.
Before any money is spent on damp treatment, get an independent RICS survey to establish what's actually causing the problem.
Myth 2: "My Walls Are Wet Because of Rising Damp — I Can See the Tide Mark"
The tide mark is actually caused by salt deposition, not water per se. As water evaporates from a wall, it leaves behind dissolved salts in a band at the evaporation level. This can persist long after the moisture source has been addressed — and can continue to show high moisture meter readings because salts are hygroscopic (they attract moisture from the air).
A tide mark doesn't prove the wall is currently wet from rising damp. It proves the wall was wet at some point in the past, and that salts were deposited. An independent investigation is required to establish current moisture levels and their source.
Myth 3: "The Damp-Proofing Guarantee Makes the Treatment Worth Doing"
Most damp-proofing companies offer 20- or 30-year guarantees on their treatments. These sound reassuring — but consider what the guarantee is actually worth. It typically covers the treatment itself (i.e., the contractor will come back and treat again if the rising damp returns), not any consequential damage caused by ongoing dampness, and not the cost of decorative reinstatement. It also relies on the company still being in business in 20 years.
More fundamentally: if the treatment is addressing the wrong problem, the guarantee is worthless. You're being guaranteed that something ineffective will be re-applied at no charge.
Myth 4: "Modern Sand-Cement Plaster Will Solve the Problem"
In Victorian buildings, the traditional lime plasters that were used originally allow moisture to move through the wall and evaporate at the surface. This is how solid brick walls are supposed to work. They breathe.
Replacing lime plaster with modern hard sand-cement render traps moisture within the wall, often making the problem significantly worse and causing the new plaster to fail rapidly. Traditional lime plaster — applied by a specialist — is almost always the right solution for an old building.
Myth 5: "I Need to Sort the Damp Before I Can Sell"
Not necessarily. This one is subtler. If your property has evidence of damp that isn't currently causing active problems, you don't always need to spend thousands treating it before you can sell. Transparency is what matters.
Our advice: get an independent RICS survey before you sell. If damp is found, understand what it is, what it would cost to address, and present that information openly to buyers. A buyer who commissions their own Level 3 survey and discovers the damp independently is in a worse negotiating mood than a buyer who's been provided with a clear, honest assessment upfront.
The Bottom Line
Before you spend a penny on damp-proofing work, commission an independent RICS survey. Our Level 3 Building Surveys include a full, independent damp assessment with no financial interest in the outcome. We'll tell you what the problem really is, what it will really cost to address, and — where appropriate — recommend specialists who can help without a conflict of interest.
Contact us today — it could save you thousands.
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Sarah Mitchell
RICS-accredited surveyor with 12+ years' experience and deep expertise in damp investigation across West London properties.