A guide to damp proofing.

Professional damp proofing involves identifying the root cause—whether it is rising damp, penetrating damp, or condensation—and applying a permanent barrier to keep your home dry. Effective treatment not only protects your health but is often a mandatory requirement for securing a mortgage or selling a property.

What Does the Work Involve?

• Site Survey: Using moisture meters and thermal imaging to map the extent of the damp and identify the source.
• Preparation: Removing salt-contaminated plaster back to the original brickwork or stone, usually up to 1.2 metres in height.
• DPC Injection: Drilling holes into the mortar course and injecting a silane-based chemical cream to create a new waterproof barrier.
• Membrane Installation: Fixing a studded plastic damp-proof membrane to the walls in cases of extreme moisture or below-ground areas.
• Tanking: Applying a waterproof cementitious coating to masonry to prevent liquid water penetration.
• Specialist Re-plastering: Applying a salt-retardant render followed by a breathable finish to prevent hygroscopic salts from reappearing.

Typical Costs

Total costs are heavily influenced by the size of the affected area and the thickness of your walls. Expect to pay more for properties with flint or stone walls, as these require more complex injection patterns and specialist materials.

How Long Does It Take?

• Initial Survey: 1–3 hours depending on the property size.
• Standard Room Treatment: 2–4 days for stripping, injection, and rendering.
• Full House Damp Proofing: 7–14 days depending on the number of external walls.
• Drying Out Period: 1 month per 25mm of wall thickness before final decorating can begin.

DIY or Professional?

While DIY injection kits are available at hardware stores, they are rarely a permanent fix for rising damp. Professional damp proofers use high-pressure equipment and specialist salt-resistant renders that are not available to the general public.

Note: Most mortgage lenders and insurance companies will only accept damp-proofing certificates issued by a qualified professional with a long-term guarantee.

Choosing the Right Tradesperson

• Check Accreditations: Look for PCA (Property Care Association) membership or CSRT (Certificated Surveyor in Remedial Treatment) qualifications.
• Insurance-Backed Guarantees (IBG): Ensure their 10–20 year guarantee remains valid even if the company goes out of business.
• Independent Surveys: Consider hiring an independent surveyor who doesn't perform the repairs to ensure an unbiased diagnosis.
• Questions to Ask:
  • Is this rising damp or just condensation?
  • Will the new plaster be salt-retardant?
  • Do you provide a written report and a floor plan of the treated areas?
  • Are your guarantees transferable to a new homeowner?

UK Regulations

• Building Regulations Part C: Covers resistance to contaminants and moisture; all new work must comply with these standards.
• BS 6576: The British Standard code of practice for diagnosing rising damp and installing chemical DPCs.
• Listed Buildings: If your home is listed, you must obtain Listed Building Consent before applying chemical treatments or membranes.

Common Problems

• Misdiagnosis: Many "rising damp" issues are actually caused by poor ventilation or leaking gutters, leading to unnecessary and expensive work.
• Bridging the DPC: High external ground levels or internal plaster touching a solid floor can "bridge" the damp course, allowing moisture to bypass it.
• Incorrect Plastering: Using standard gypsum plaster over a new DPC will fail, as it cannot cope with residual salts in the brickwork.
• Failure to Fix the Source: Injecting a wall without fixing a leaking pipe or blocked air brick will result in the damp returning within months.

Frequently Asked Questions