Treat penetrating damp.

Left untreated, this moisture causes unsightly staining, "blown" plaster, and structural timber decay. Addressing the root cause and applying professional water-repellent treatments is essential to protect your home’s value and maintain a healthy living environment.

What Does the Work Involve?

• Comprehensive Survey: A specialist uses moisture meters to map the damp and identifies external entry points such as cracked masonry, porous bricks, or faulty pointing.
• Source Remediation: Before treating the wall, the tradesperson ensures external defects—like leaking downpipes or damaged roof tiles—are repaired.
• Surface Preparation: External walls are cleaned of moss, algae, and loose debris to ensure the treatment can penetrate the substrate effectively.
• Application of Water Repellents: A breathable, silane-based cream or liquid is applied to the masonry, creating a hydrophobic barrier that stops liquid water while allowing vapour to escape.
• Internal Remediation: If internal plaster is salt-contaminated or "blown," it is stripped back and replaced with specialist lime-based or salt-retardant plaster.

Typical Costs

Prices for penetrating damp treatment vary based on the height of the building and the extent of the masonry repairs required. These 2025/26 estimates include VAT and professional labour rates.

Factors affecting the final bill include the porosity of your brickwork, the need for scaffolding, and whether the damp has caused secondary issues like dry rot in floor joists.

How Long Does It Take?

• Initial Survey: 1–2 hours to identify the cause and measure moisture levels.
• External Treatment: 1 day for a standard semi-detached gable end or front elevation.
• Masonry Repairs: 1–3 days if significant repointing or render patching is required.
• Internal Drying: 4–12 weeks for walls to fully dry out naturally after the source is blocked.

DIY or Professional?

While DIY "waterproof" paints are available at hardware stores, they often trap moisture inside the brick, worsening the problem over time. Professional-grade silane creams are breathable, which is vital for the health of UK masonry.

Identifying the exact source of ingress requires experience; a professional damp proofer has the thermal imaging and moisture mapping tools to ensure you aren't just masking a symptom. If the work involves structural repairs or chemical injection, hiring a specialist is highly recommended to secure a guarantee.

Choosing the Right Tradesperson

• Check Qualifications: Look for members of the Property Care Association (PCA) or those with CSRT (Certificated Surveyor in Remedial Treatments) status.
• Insurance-Backed Guarantees: Ensure they offer a 10–20 year guarantee that remains valid even if the company stops trading.
• Red Flags: Be wary of "specialists" who recommend a damp-proof course (DPC) for a problem clearly caused by a leaking gutter or porous brickwork.

Ask your tradesperson: "Is this treatment breathable, and will it prevent the bricks from 'spalling' during a freeze-thaw cycle?"

UK Regulations

• Part L Building Regs: If you are removing more than 50% of an internal wall's plaster, you may be required to upgrade the thermal insulation of that wall.
• Listed Buildings: If your home is listed, you must obtain Listed Building Consent before applying any chemical treatments or changing the mortar type.
• Health and Safety: Contractors should provide a RAMS (Risk Assessment and Method Statement) if working at height or using chemical sprays.

Common Problems

• Misdiagnosis: Treating a wall for penetrating damp when the real issue is internal condensation due to poor ventilation.
• Bridged Cavities: Water crossing from the outer leaf to the inner leaf via debris or insulation "snags" inside the wall cavity.
• Incompatible Mortar: Using modern cement to repoint an old lime-mortar wall, which forces moisture into the bricks and causes them to crumble.
• Treating Symptoms Only: Applying a waterproof coating without fixing the cracked pipe or slipped tile that caused the leak.

Frequently Asked Questions