Damp proofing is an unusually easy trade to get wrong as a customer, because you generally cannot check the work. Once the plaster is back on, you are trusting that what happened behind it was correct — and you will not find out for two or three years.
So the decision has to be made on evidence available beforehand. Here is what to look at.
1. Are they accredited, and by whom?
Anyone can print "damp specialist" on a van. The meaningful accreditations in this trade are:
Property Care Association (PCA) membership. Full membership means audited standards on workmanship and materials, and a guarantee as standard. This is the main one.
TrustMark — the government-endorsed quality scheme. You can look up any registered firm and see their record; ours is here.
Qualitymark Protection accredited installer status.
Ask which they hold, then check it independently rather than taking a logo on a website as proof. All three schemes publish searchable registers.
2. Does the survey identify the cause, or just the treatment?
This is the single most important question in this article.
Damp, woodworm and rot are almost always symptoms. Something is keeping the fabric wet: a failed damp proof course, a leak, blocked ventilation, ground levels raised above the DPC, condensation from an unvented bathroom.
A report that specifies treatment without naming the cause has skipped the part that determines whether the repair lasts. Injecting a wall or spraying timber addresses what you can see. If the water is still arriving, you will be doing it again.
So read the report and ask: what is making this wet, and is fixing that included in the price?
3. Do you get it in writing before committing?
You should receive a written report setting out:
what the problem is, and the evidence for that conclusion
what is causing it
which areas are affected, and how badly
what work is recommended, in what order
what it costs
Verbal reassurance and a number on the back of a card is not a survey. If a firm will not put the diagnosis in writing before you commit, that tells you something.
4. Is the diagnosis actually right?
An uncomfortable number of the properties we survey have been misdiagnosed before we arrive — sometimes by people selling the treatment.
The most common error by a wide margin is condensation sold as rising damp, because a chemical damp proof course is a far larger job than improving ventilation. They look similar and need entirely different work. Our guide on rising damp or condensation sets out how to tell, so you can sanity-check what you are told.
Two other frequent ones:
Woodworm treated as active when it is dormant. Old holes from decades ago need nothing at all. See is my woodworm still active.
Tanking specified where a damp proof course would do, or vice versa. Cementitious tanking is for below-ground walls under water pressure, and it is a much bigger job than a DPC.
A good firm will sometimes tell you that you need less than you feared. That is a reasonable signal to trust them.
5. What does the guarantee actually cover?
Ask three things:
How long, and what precisely is covered — the treatment, the plaster, both?
Who honours it if the firm ceases trading? PCA members can offer insurance-backed guarantees that survive the company. An in-house promise from a firm with no backing is worth what the firm is worth.
What voids it? Some guarantees are conditional on maintenance or on the cause being addressed.
6. How long have they been doing it, locally?
Longevity matters more here than in most trades, precisely because failures surface years later. A firm that has been trading locally for decades has had time to be found out.
It also means they know the local stock. Damp in a Belfast solid-wall terrace behaves differently from damp in a coastal property in Bangor taking wind-driven rain, or a lakeside house near Enniskillen with a high water table. Someone who works across the province every week recognises the pattern.
7. Will the treatment suit the building?
Two things to ask, particularly for older property:
Is it appropriate for the construction? Solid stone and brick walls with lime mortar are designed to breathe. Cement render and impermeable paints trap moisture inside and cause more damage than they prevent. If a contractor proposes sealing a breathing wall, ask how the wall is then meant to dry.
How disruptive is it? Modern low-odour, water-based, non-flammable treatments let a building stay occupied. Older solvent-carried products did not. For a home with children, or a business that has to keep trading, that is a practical difference.
For listed buildings there is a further layer — alterations need consent from the Historic Environment Division, and a specification proposing removal of original fabric may not receive it.
8. Is it a survey, or a sales call with a meter?
Firms price surveys differently, and either approach can be thorough or perfunctory — so what you pay tells you very little on its own. What matters is whether the visit is genuinely diagnostic.
Signals that it is not: pressure to sign on the day, a discount that expires this week, a diagnosis reached in under ten minutes without lifting a floorboard or getting into the roof space, and no written report.
A survey carried out properly — floorboards up, meters used, roof space entered, cause identified in writing — is worth considerably more than a quick look from the hallway. Ours are chargeable for that reason: it is a surveyor's time and a written diagnosis, not a sales visit.
A short checklist
Before you agree to anything:
Accreditations named, and verified independently
Written report received
The cause stated, not just the treatment
Fixing the cause included in the price
Guarantee terms understood, including who honours it
Treatment appropriate to the construction
No pressure to decide on the day
Where we stand on all of this
We are a family firm, trading in Northern Ireland since September 1967, with more than 40,000 contracts completed. We are Property Care Association members, TrustMark registered and a Qualitymark Protection accredited installer — our accreditations set out what each covers.
You get a written report setting out the cause and the cost before committing, and we will tell you when you need less than you expected. Properties we treated three decades ago have been reinspected since with no recurrence.
If you would like a survey, get in touch or ring 028 9061 8343. We cover the whole province.