Rising Damp Treatment: What to Expect from Start to Finish

Rising Damp Treatment: What to Expect from Start to Finish

You have had a surveyor look at your property and they have told you the words nobody wants to hear: rising damp. Now you need to know what actually happens next: how the treatment works, how long it takes, how much it costs, and whether it will last. This guide walks you through the entire process without the jargon.

What Rising Damp Actually Is

Rising damp is ground moisture moving upward through masonry (brick, stone, or mortar) by capillary action. Think of it like water being drawn up through a series of very fine tubes. The moisture carries dissolved salts from the ground, and as the water evaporates from the wall surface, those salts are deposited. This is what creates the characteristic tide mark at low level, usually below 1.2 metres, along with the powdery, crystalline deposits on wall surfaces known as efflorescence.

Historically, buildings relied on physical damp proof courses (DPCs), typically a layer of slate, lead, or bitumen at or near ground level, to interrupt this capillary pathway. When these fail, degrade, or are absent (as in many Victorian and Edwardian properties), rising damp can establish itself through the wall fabric.

Step One: The Survey, and Why Nothing Should Happen Without It

A professional damp survey is the foundation of any rising damp treatment. Without it, you are guessing at the cause, the extent, and the correct remedy.

During a rising damp survey, a qualified surveyor will:

• Take moisture readings at multiple points across the wall using a calibrated moisture meter
• Inspect the external ground levels (a high external ground level bridging the DPC is a common cause)
• Check for bridged air bricks and blocked subfloor ventilation
• Look for evidence of plumbing leaks that may be mimicking rising damp
• Assess the condition of any existing DPC
• Identify whether the plaster is salt-contaminated

The survey produces a written report confirming the diagnosis, the extent of affected walls, and a recommended treatment specification. Do not proceed with any contractor who skips this stage or offers a rising damp treatment over the phone without a site visit.

Step Two: How Chemical DPC Injection Works

The most widely used rising damp treatment in the UK is chemical damp proof course injection. Here is the process, step by step:

1. Drilling

A series of holes are drilled into the mortar course at low level, typically 150mm above external ground level. Holes are spaced approximately 100 to 120mm apart along the affected wall length. In a 230mm (9-inch) solid brick wall, holes are usually drilled at a slight downward angle to allow fluid to penetrate fully. For thicker or cavity walls, the specification changes accordingly.

2. Injection

A silane or siloxane-based chemical cream or fluid is injected into the drilled holes. Modern injection creams are the standard. They are cleaner than fluid injection, less likely to be diluted by existing moisture in the wall, and more reliable in terms of even distribution. The chemical migrates through the masonry and reacts to form a water-repellent barrier, effectively a new DPC in situ.

3. Hole filling

Once injection is complete and the product has been given time to penetrate, the drill holes are filled with mortar or plugged. The wall is then ready for the next stage.

Step Three: Why the Plaster Must Be Replaced

This is the part many homeowners do not expect. Once the chemical DPC is in place, the existing plaster must come off, all of it in the affected area, typically to a height of 1.2 to 1.5 metres above floor level.

Why? Because the existing plaster has been contaminated by the salts carried up by the rising damp. Even after the DPC injection stops further moisture movement, those hygroscopic salts remain in the plaster. They will continue to attract moisture from the air, creating damp patches that look identical to ongoing rising damp, even though the source has been stopped. If the old plaster is left in place, the treatment appears to have failed.

Replacement plaster must be a salt-resistant (renovating) plaster. Standard browning or bonding plaster is not appropriate. It is not formulated to resist the salt migration that will continue from the residual salts in the masonry.

Timeline: What to Expect and When

The most common source of frustration is the drying time. Homeowners sometimes expect walls to look perfect within weeks of injection. The full remediation cycle (from injection to completed redecoration) often takes 4 to 8 months, with most of that time spent waiting for the masonry to dry out and the new plaster to cure.

Guarantees: What You Should Expect

Reputable rising damp contractors provide guarantees backed by the Certificated Surveyor in Remedial Treatments (CSRT) qualification and, for injection-based treatments, guarantees registered with the Chemical Injection Guarantee Association (CIGA). CIGA-backed guarantees run for 20 to 30 years and are transferable to a new owner if the property is sold, which matters for buyers and mortgage lenders.

A guarantee is only as good as the contractor who provides it. Always check that the contractor is a CSRT member and that the guarantee paperwork is properly registered, not just printed on headed paper.

Will Rising Damp Come Back?

Properly executed rising damp treatment should not fail within the guarantee period. When rising damp returns after treatment, the most common causes are:

• Ground levels not addressed: If external ground level was bridging the original DPC and was not lowered as part of the remediation, moisture will continue to bridge the new chemical DPC
• Old plaster not replaced: Salt-contaminated plaster left in place will continue to show damp symptoms regardless of whether the source has been stopped
• Incorrect diagnosis: The original problem was not rising damp at all, penetrating damp or a plumbing leak was the actual source, and DPC injection was the wrong treatment
• Poor installation: Insufficient drilling depth, incorrect hole spacing, or wrong product specification

If you have rising damp symptoms in a property that has already been treated, a new survey is the starting point. Read more about our full damp proofing service.

Cost Range for Rising Damp Treatment

Rising damp treatment costs depend on the length of affected wall, the wall construction, whether tanking is required in addition to injection, and local labour rates. Broad ranges in 2026:

• Chemical DPC injection only: priced per linear metre of affected wall
• DPC injection including hack-off and replastering: the replastering usually costs more than the injection itself
• Full treatment including multiple walls: scales with the number of walls and the plaster area
• Large Victorian terrace with extensive rising damp: the top of the range, always specified after a survey

These figures should be confirmed by a survey and written quotation. Prices in London run higher than in Surrey and Kent due to labour costs.

Red Flags When Getting Quotes

Rising damp is unfortunately an area where cowboy operators are common. Watch for:

• A quote provided without a physical site visit
• No written survey report or specification
• High-pressure sales tactics with “today only” discounts
• Claims that their proprietary system is the only effective method
• No CSRT qualification or CIGA-registered guarantee on offer
• Extremely low prices: a whole-room treatment that includes replastering cannot credibly be done for a token sum
• No mention of replacing the plaster (this is a fundamental step, any contractor who plans to leave old plaster in place and redecorate over it is not doing a proper job)

Frequently Asked Questions