How to Hire a Damp Proofing Company

What makes hiring a damp proofer different

This is the trade where the person diagnosing the problem is usually the person selling the cure, and that conflict of interest causes more unnecessary expenditure than anything else in home improvement.

A damp company's surveyor arrives, uses a moisture meter on a wall, and recommends a chemical damp proof course with replastering. The homeowner has no way to assess whether that is the right answer, and the survey was free precisely because it is a sales visit.

Meanwhile the actual cause is frequently something else entirely, and cheaper.

Get an independent diagnosis first

Engage a surveyor who does no remedial work, and pay them. An independent damp and timber survey costs money, and it routinely saves multiples of its fee by identifying a cause that does not require injection at all.

This one step is the single highest-value action a homeowner can take in this trade.

What actually causes damp

• Condensation, by far the most common, and it is a ventilation and heating problem, not a damp-proofing one
• Penetrating damp, failed pointing, cracked render, defective flashing, leaking gutters or downpipes
• Bridging, raised external ground levels, debris in a cavity, or render carried below the damp course
• Plumbing leaks, slow, hidden, and easily mistaken for rising damp
• Blocked or covered airbricks, under suspended floors
• Rising damp, real but considerably less common than the volume of treatment sold implies

Moisture meters used on plaster measure conductivity, and salts in plaster affect readings. A high reading is not by itself a diagnosis.

What a good approach looks like

A competent surveyor investigates before concluding: checks external ground levels, gutters and downpipes, pointing and render, ventilation, and the internal environment. They consider condensation seriously rather than dismissing it.

They explain what they think is happening and why, and they are willing to be questioned.

Be wary of: a diagnosis reached in minutes, a recommendation identical to the one given to your neighbour, pressure to book immediately, and a free survey followed by a quote for thousands.

Deposits and payment stages

Treatment work is labour-heavy rather than material-heavy, so no deposit should be needed at all. A damp company asking for a substantial payment before starting is asking you to fund something other than materials.

Hold the final 10% until after replastering has dried and been decorated, because that is when failures show.

What usually goes wrong

• Chemical injection installed where the cause was condensation, so the damp returns
• Replastering that traps the real problem behind it
• Thirty-year guarantees from companies that dissolve within five
• External causes, gutters, ground levels, left unaddressed
• The same damp returning, blamed on a new and different cause

Questions to ask

• What do you think is causing this, and what did you check to reach that?
• Have you looked at ground levels, gutters, pointing and ventilation?
• Why is it not condensation?
• Is your guarantee insurance-backed, and who underwrites it?
• What happens if the damp returns?
• Are you a member of a trade body, and can I verify it?