Damp proofing a wall typically involves removing affected plaster, injecting a silicone-based damp-proof cream into the mortar joint, and applying a waterproof protective layer. In most cases, holes are drilled at regular 12 cm intervals before the cream is injected to create a new damp-proof course. The treated area is then sealed, replastered, and finished to help prevent rising damp from returning.
The Damp Proofing Process Step By Step
| Stage | Description | Key Details | Purpose |
|---|---|---|---|
| 1. Assessment | Identify the type and extent of damp affecting the wall | Confirm the issue is rising damp rather than condensation or penetrating damp before treatment begins | Ensure the correct repair method is used |
| 2. Preparation | Remove affected materials and expose the mortar joint | Remove skirting boards, damaged plaster, salts, and debris to expose the injection line | Allow proper access for chemical DPC installation |
| 3. Drilling | Drill holes into the mortar bed for cream injection | Drill 12–14mm holes at 100–120mm centres, typically 150mm above external ground level. Holes should stop 10–20mm before the opposite wall face | Create channels for the damp-proof cream |
| 4. Injection | Inject chemical damp-proof cream into the wall | Use a silane/siloxane cream injected with a low-pressure applicator until each hole is filled completely | Form a water-repellent damp-proof barrier |
| 5. Curing & Drying | Allow the treatment to cure and walls to dry | The cream disperses through the mortar and cures over approximately 4–6 weeks while moisture gradually evaporates from the wall | Prevent further rising moisture |
| 6. Replastering | Replace contaminated plaster with a suitable finish | Apply salt-resistant render or replastering system after treatment to prevent residual salts damaging decorations | Restore the wall surface and improve durability |
| 7. Final Finishing | Decorate and monitor drying progress | Repaint using breathable finishes where appropriate and ensure moisture levels continue to reduce | Complete the repair and maintain long-term protection |
Important Chemical DPC Installation Guidelines
| Guideline | Recommendation |
|---|---|
| DPC Height | Install the chemical DPC at least 150mm above external ground level and above internal floor level to avoid moisture bridging |
| Hole Position | Drill into the mortar joint rather than directly into the bricks |
| Thick Walls | For walls thicker than 400mm, injection may be required from both sides in a staggered or zigzag pattern |
| Drying Time | Walls can take several weeks or months to fully dry depending on thickness and moisture levels |
| Professional Assessment | A damp survey should confirm the source of moisture before treatment is carried out |
Important Chemical DPC Installation Guidelines
Correct installation is essential for a chemical damp-proof course (DPC) to work effectively and prevent rising damp from returning. Professional damp-proofing specialists follow strict guidelines to ensure the moisture barrier performs properly over the long term.
| Guideline | Best Practice |
|---|---|
| DPC Height | The chemical DPC should normally be installed at least 150mm above external ground level to prevent moisture bridging |
| Hole Position | Injection holes should be drilled directly into the mortar joint rather than the bricks |
| Hole Spacing | Holes are typically drilled at 100–120mm centres to create a continuous barrier |
| Drilling Depth | Holes should stop approximately 10–20mm before the opposite side of the wall |
| Thick Walls | Walls thicker than 400mm may require drilling from both sides in a staggered pattern |
| Wall Preparation | Damaged plaster and salt contamination should be removed before treatment begins |
| Drying Conditions | Adequate ventilation and heating help walls dry more efficiently after treatment |
| Professional Diagnosis | The source of damp should always be confirmed before installing a chemical DPC |
What Happens After Damp Proofing?
Once the chemical damp-proof cream has been injected, the wall will gradually begin to dry out. However, damp-proofing is not an instant process, and the wall may take several weeks or months to fully dry depending on its thickness, moisture levels, and ventilation conditions.
Drying Period
After injection, the damp-proof cream cures inside the mortar joint and forms a water-repellent barrier. Moisture already trapped within the wall must then evaporate naturally over time.
In most cases:
- Initial curing takes around 4–6 weeks
- Full wall drying may take several months
- Good airflow and heating can speed up drying
Walls with severe rising damp or thick masonry may require a longer drying period.
Replastering the Wall
Contaminated plaster is usually removed before treatment because it often contains salts left behind by moisture. These salts can continue attracting water even after the damp source has been fixed.
Once the wall is ready:
- A salt-resistant render or replastering system is applied
- The surface is left to cure properly
- Decorations can then be restored safely
Using the correct replastering materials helps prevent staining, bubbling paint, and future plaster damage.
Decorating Timelines
It is important not to redecorate too early after damp proofing. Applying paint before the wall has dried properly can trap moisture inside the surface.
As a general guide:
| Stage | Typical Timeline |
|---|---|
| Chemical DPC installation | Day 1 |
| Initial curing period | 4–6 weeks |
| Replastering | After drying begins |
| Painting and decorating | Usually after plaster has fully cured |
Breathable paints are often recommended during the early drying stages to allow any remaining moisture to escape naturally.
FAQ
How is damp proofing done?
By drilling into the mortar bed and injecting a water-repellent cream to block rising moisture.
Can damp proofing be done without removing plaster?
Not effectively. Contaminated plaster must be removed to prevent salts from reappearing.
How long does damp proofing last?
correctly installed chemical DPC can last 20–30 years or more.
Get Help Now
Damp proofing is both a preventive and restorative process. Done correctly, it protects your home from structural damage, health risks, and costly repairs.
If you suspect rising or penetrating damp, don’t ignore the signs.
👉 Contact Damp and Mould Solutions Ltd for a professional damp survey, guaranteed treatments, and expert guidance on keeping your walls dry long-term.