20- or 30-year guarantees on damp treatment: what to check

What is a 20- or 30-year damp treatment guarantee worth?

Guarantees of 20 or 30 years are common for treatments against damp rising from the ground, such as injections (chemical damp-proof course) and electro-osmosis. The number is impressive, but on its own it says little. What matters is the wording: which area is covered, what counts as a failure, what the company does in that case and what voids the guarantee.

Think of the guarantee as part of the contract, not a sales argument. A 30-year guarantee with broad exclusions may protect you less than a 10-year one with clear terms. And a guarantee is only worth something while there is someone to honour it.

Before discussing guarantees, make sure the proposed treatment tackles the right cause. Many stains at the base of walls are condensation or water ingress, and no rising-damp guarantee covers them. The free diagnosis gives the likely cause in a few minutes.

The company's commercial guarantee does not replace the rights the law already gives you as a consumer if the work is defective. The time limits and conditions of those rights depend on the type of contract; check with a lawyer or with DECO, the consumer association.

What the guarantee should cover: area, method and result

A useful guarantee answers three questions in writing. If any is left unanswered, ask for it to be added before signing.

• Where: the treated area, in linear metres or m², identified on a plan or in photos with measurements. Without this, it is easy for the company to say a new stain is "outside the treated area".
• What: whether it covers only the product applied, the workmanship, or the measured result — for example, wall moisture falling below a given value by a set date.
• How: what happens if the treatment fails. Free re-treatment of the affected area, repair of finishes, partial refund, or just an assessment visit?

Most guarantees in this market offer re-treatment of the area, not a refund. That can be reasonable, but check whether it also includes stripping and redoing the plaster and repainting, which are often the most expensive part of the job.

Common exclusions: what usually voids the guarantee

Reading the exclusions is the most important part. Some are reasonable; others empty the guarantee in practice.

One exclusion that deserves attention is salts. Even once rising water is stopped, salts left in the old plaster keep drawing moisture from the air and staining the wall. If the affected plaster isn't replaced, the stain can return without the treatment having failed — and the guarantee, fairly, won't cover it. See the guide salt deposits on walls.

Does the guarantee pass to the new owner if you sell?

Not always. Many guarantees are personal, issued in the name of whoever signed the contract, and end with the sale. Others are tied to the property and pass to the buyer, sometimes after written notice to the company or payment of a fee.

If you might sell in the coming years, ask for transferability to be written into the contract. For buyers, a transferable, well-documented guarantee is useful information; a guarantee that no longer applies is just paper. The guide buying a home with damp explains what to ask the seller for.

• Does it say the guarantee follows the property rather than the person?
• Must the company be notified of the sale? Within what period and how?
• Is there a transfer fee?
• Does the new owner receive the readings and the report from the original work?

What if the company closes? Who honours the guarantee

A commercial guarantee is a promise from the company. If the company closes, there may be nobody left to honour it — and 20 or 30 years is a long time for any business. It is a legitimate question, and a serious company won't take offence.

• Who issues the guarantee: the company that did the work, the product manufacturer, or both? A manufacturer's guarantee may survive the installer closing, although it usually covers only the product.
• Insurance: ask whether the company has liability insurance and whether any policy backs the guarantee. Ask for the insurer's name in writing.
• Identification: check the tax number (NIF), registered office and alvará or contractor's certificate with IMPIC, the construction regulator. Be wary of companies that change name frequently.
• Agents and franchises: if the company is part of a network, who honours the guarantee if that local agent closes?

It also helps to ask how many years the company has traded under the same tax number and to request contacts of customers whose work is several years old. A new company can be competent, but it has no track record yet showing how it honours long guarantees.

There is no way to remove this risk completely. But a guarantee with recorded readings, a defined area and a technical report keeps its value as evidence, even if you have to turn to another company.

Documents to keep during and after the work

Keep everything in one folder, on paper and digitally. In 15 years nobody will remember what was agreed verbally.

1. Written diagnosis with the identified cause and initial readings.
2. Detailed quote, with area in m² or linear metres, method, product and unit price.
3. Signed contract and the full text of the guarantee, with exclusions and maintenance conditions.
4. Dated photos before, during (with drill holes or electrodes visible) and after the work.
5. Invoices and payment receipts.
6. Technical data sheet of the product used and, if there is one, the manufacturer's guarantee.
7. Records of follow-up visits and new readings, with dates.

To compare proposals before signing, use the questions in the guide how to choose a damp company. Observed prices for injections and electro-osmosis (€35–60/m²) are in how much injections cost.

How to claim on the guarantee if the damp comes back

1. Photograph the area and measure the height of the stain, with the date. Repeat over a few weeks to show how it develops.
2. Confirm the stain is inside the treated area and there is no other obvious cause, such as a leak, a blocked drain or condensation behind furniture.
3. Notify the company in writing (email or letter), citing the contract and guarantee, and ask for a visit within a set period.
4. Ask for the visit to include readings and a written report with its conclusion.
5. If there is no reply or it isn't satisfactory, use the Livro de Reclamações (the official complaints book, also available online) and seek support from DECO or a lawyer.

If the company says the cause is something else, ask it to back that up with readings. You can also ask for a free second opinion on the report or on a new proposal. To understand how rising damp is told apart from other causes, read the guide to rising damp.