Help Guide

How to Stop Rising Damp

Rising damp will not go away on its own. This guide explains the proven methods for stopping rising damp effectively, what to avoid, and how to ensure the treatment actually works.

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Understanding How Rising Damp Works in Suffolk, Norfolk & Essex

To stop rising damp, you first need to understand the mechanism that drives it. Rising damp is caused by capillary action — the same physical process that allows a plant to draw water up from its roots to its leaves, or a paper towel to absorb a spill. Water is drawn up through the tiny pores and capillaries in masonry materials (brick, stone, mortar, and concrete) against the force of gravity.

The height to which water can rise depends on the size of the pores in the material. Smaller pores create stronger capillary action, which is why water rises higher in fine-grained materials. In a typical brick wall, capillary action can draw water up to approximately 1.2 metres above ground level, though this varies. The moisture rises until the rate of capillary uptake is balanced by the rate of evaporation from the wall surface.

As the moisture rises through the masonry, it carries dissolved salts — primarily chlorides and nitrates from the ground, and sulphates from the bricks and mortar. These salts are deposited in the plaster and on the wall surface as the water evaporates. The salts are hygroscopic, meaning they absorb moisture from the air. This creates a vicious cycle: even if the rising damp is stopped, the salt-contaminated plaster continues to attract atmospheric moisture and appears damp.

Proven Methods for Stopping Rising Damp in Suffolk, Norfolk & Essex

1. Chemical DPC Injection

Chemical injection is the most widely used and cost-effective method for installing a new damp proof course in an existing building. The process involves drilling holes into the mortar course at the base of the wall and injecting a water-repellent chemical that permeates through the surrounding mortar and masonry, creating a continuous barrier that prevents water from rising further.

Modern injection systems use a silicone-based cream (thixotropic cream) rather than the older fluid siliconate solutions. The cream is denser and stays in the injection hole rather than flowing away, providing more consistent and reliable coverage. It is injected under low pressure into holes drilled at approximately 120mm centres, at a slight downward angle, to about two-thirds of the wall thickness.

The silicone cream works by lining the pores and capillaries of the mortar with a water-repellent coating. Water can no longer be drawn up by capillary action through the treated zone. The cream does not block the pores entirely, so the wall remains breathable — moisture vapour can still pass through, which aids the drying process above the injection line.

What Makes a Good DPC Injection?

Correct hole spacing — 120mm centres is standard. Wider spacing leaves gaps that moisture can pass through
Correct drilling depth — approximately two-thirds of the wall thickness for solid walls. Too shallow and the barrier does not extend far enough; too deep risks breaking through the other side
Correct mortar course selection — the injection should be in the mortar course closest to external ground level, ideally at least 150mm above it
Full coverage — every wall in contact with the ground must be treated, including internal walls with foundations. Missing a wall or a section creates a bypass route for moisture
Cavity walls — both the inner and outer leaves must be injected separately. Injecting only one leaf leaves the other as a pathway for rising moisture
Quality product — using an independently tested silicone cream ensures the product has been proven effective for long-term damp protection

2. Addressing DPC Bridging

In many cases, a property has a perfectly functional DPC that has been inadvertently bypassed. Addressing the bridging can sometimes resolve the rising damp without the need for injection. Common bridges and their solutions:

Raised External Ground Levels

Over decades, garden soil, paths, patios, and driveways can be built up to a level above the DPC. This allows moisture to bypass the DPC and enter the wall above it. The solution is to lower external ground levels to at least 150mm below the DPC line. Where this is not possible (for example, a patio at a fixed level), installing a French drain or a vertical DPC on the face of the wall below ground level can provide an alternative barrier.

External Render Bridging the DPC

Cement render applied to an external wall that extends below the DPC line allows moisture to travel up behind the render, bypassing the DPC. The render should be cut back to at least 150mm above external ground level to expose the DPC line and prevent bridging. A bellcast bead at the base of the render helps direct rainwater away from the wall.

Internal Floor Level Above DPC

If internal floor levels have been raised — for example, by laying a new concrete slab or adding floor coverings on top of the original floor — the DPC may now be below the floor level, allowing moisture to bypass it. Adjusting the internal floor level or extending the DPC upwards may be necessary.

Debris or Soil Against the Wall

Rubble, soil, leaves, or stored materials piled against an external wall above the DPC act as a moisture bridge. Simply clearing these materials and maintaining a gap between the wall and any ground-level features can resolve the problem.

3. Proper Replastering After Treatment

This step is as important as the DPC injection itself, yet it is the one most commonly done incorrectly. After the DPC has been installed, the contaminated plaster must be removed and replaced with a specialist renovating plaster system. Here is why each step matters:

Strip Contaminated Plaster

Remove all plaster from the affected wall to at least 300mm above the highest point of visible dampness. The plaster is saturated with hygroscopic salts (chlorides, nitrates, sulphates) that have been carried up by the rising moisture over years or decades. These salts attract moisture from the air, so even with a working DPC, the old plaster will appear damp indefinitely. It must be completely removed.

Apply Salt-Inhibiting Render

A salt-inhibiting base coat render is applied to the bare masonry. This render contains additives that prevent salts from migrating from the masonry into the new plaster. It is applied at a minimum thickness, ensuring complete coverage of the stripped area. Some systems also include a waterproofing additive in this base coat.

Apply Renovating Plaster Finish

A specialist renovating plaster skim coat is applied over the render. Renovating plaster is designed to be highly breathable — it allows moisture vapour to pass through, which aids the drying process of the underlying masonry. At the same time, its pore structure prevents the passage of dissolved salts, so even if some residual salts migrate from the masonry, they are trapped within the render layer and do not reach the finished surface.

What Does NOT Stop Rising Damp in Suffolk, Norfolk & Essex

Waterproof paint

Painting the inside of a wall with a waterproof or damp-seal paint does not stop rising damp. It simply traps the moisture behind the paint film. The damp will eventually push the paint off the wall, often causing worse damage than before.

Standard plaster

Replastering with ordinary gypsum plaster after DPC injection is the most common cause of apparent treatment failure. Gypsum plaster absorbs salts from the masonry and attracts atmospheric moisture, making the wall look damp even though the DPC is working perfectly.

Dehumidifiers

Dehumidifiers reduce air moisture and help with condensation, but they have no effect on rising damp. The moisture is being drawn up through the masonry by capillary action within the wall structure, not from the air.

Ventilation alone

Better ventilation increases the rate of evaporation from the wall surface, which may slightly lower the visible tide mark, but it does not stop the capillary uptake of moisture from the ground. The wall remains damp internally even if the surface appears slightly improved.

After Treatment: What to Expect in Suffolk, Norfolk & Essex

After rising damp treatment, it is important to have realistic expectations about the drying process:

The DPC starts working immediately, but the wall above the injection line is already saturated with moisture that needs to evaporate — this takes time
Thick walls (400mm or more) will take longer to dry than thin walls. A thick solid brick wall may take 12 months or more to dry fully
Good ventilation and moderate heating will speed up the drying process. Keep rooms well-aired and maintain a consistent background temperature
Do not apply non-breathable finishes (vinyl wallpaper, oil-based paint) until the wall is confirmed dry by moisture meter readings. Breathable emulsion or limewash can be used in the meantime
The renovating plaster will initially feel slightly cool to the touch as it allows moisture to evaporate through it — this is normal and is the plaster doing its job
Monitor the treated area through the first winter. If damp patches reappear, contact the specialist who carried out the treatment for a follow-up inspection

Need to Stop Rising Damp?

KDS Property Preservation provides expert rising damp diagnosis and treatment across Suffolk, Norfolk and Essex. We identify the cause accurately, recommend the right solution, and carry out the work properly — including the critical replastering stage. Contact us for a free, no-obligation inspection.

Frequently Asked Questions in Suffolk, Norfolk & Essex

Yes. A correctly installed chemical damp proof course using modern silicone-based cream injection will prevent groundwater from rising through the treated mortar course. Combined with proper replastering using renovating plaster and the removal of any DPC bridges (such as raised external ground levels), this provides a long-lasting solution. The silicone cream does not degrade over time, so the treatment is designed to provide many decades of effective protection.

There are alternative approaches, although chemical injection remains the most widely used and proven method. Physical DPC insertion involves cutting into the wall and inserting a new physical barrier (plastic or stainless steel), but this is more disruptive and expensive. Electro-osmotic systems use an electrical charge to repel moisture, but their effectiveness is debated among building professionals. Reducing external ground levels and addressing DPC bridging can sometimes resolve the problem without injection if the original DPC is intact but bypassed.

The chemical DPC begins working immediately upon injection — the silicone cream diffuses through the mortar and masonry within hours, creating the water-repellent barrier. However, the wall will not appear dry straight away because the masonry above the injection line is already saturated and needs time to dry out. Depending on wall thickness and ventilation, this drying process takes 6 to 12 months. Using renovating plaster helps manage this transition period.

No. A dehumidifier reduces the moisture content of the air, which helps with condensation problems, but it has no effect on rising damp. Rising damp is moisture being drawn up through the wall from the ground — it is driven by capillary action within the masonry, not by the humidity of the air. The only way to stop rising damp is to install an effective damp proof course that physically blocks the upward movement of water through the wall.

Improved ventilation will help surface moisture evaporate more quickly and will reduce condensation, which is often confused with rising damp. However, it will not stop genuine rising damp. The rate of evaporation may increase, causing the tide mark to appear slightly lower, but the fundamental problem — water rising through the masonry — continues. Ventilation is important as part of the overall treatment plan, but it is not a substitute for a damp proof course.

If a previous DPC injection appears to have failed, the most common causes are: standard gypsum plaster was used instead of renovating plaster (allowing hygroscopic salts to attract moisture), the original diagnosis was wrong (the problem was actually condensation or penetrating damp), the injection was incomplete (gaps in the treatment line), or external bridging was not addressed (ground levels or render bypassing the DPC). A fresh inspection to identify the actual cause is the essential first step.

Yes. KDS Property Preservation provides rising damp treatment across Suffolk, Norfolk and Essex. We serve Ipswich, Norwich, Colchester, Bury St Edmunds, Chelmsford, Great Yarmouth, Lowestoft, Woodbridge, Sudbury, Felixstowe, Stowmarket, and all surrounding areas. Contact us for a free inspection.