Domakihub How to Inject a Damp-Proof Course and Stop Rising Damp
A step-by-step guide to installing a chemical DPC in existing masonry walls.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
Rising damp is a slow destroyer of plaster, paint, and structural mortar — and it is common in older stone and brick buildings across Greece, from Athenian apartment blocks to island holiday villas. The video above shows a specialist team drilling and injecting a chemical damp-proof course on a real wall; this article walks through the same process step by step, explains what materials you need, and tells you when the work crosses into licensed-contractor territory. Whether you manage a single home or a portfolio of holiday rentals, understanding the process helps you brief a contractor, check the quality of their work, and decide when a DIY approach is realistic.
What Is a Chemical Injected DPC and Why Does It Work?
A damp-proof course (DPC) is a horizontal barrier built into a wall to stop groundwater wicking upward through capillary action — the mechanism behind rising damp. Traditional buildings constructed before the 1960s often have no DPC, or have one made of slate, lead, or bitumen felt that has cracked or been bridged by render or raised external ground levels.
Chemical injection replaces or supplements the old barrier by forcing a water-repellent silane or silicone cream into the mortar bed joints of the wall. As the cream cures, it polymerises inside the pore structure of the masonry and creates a continuous hydrophobic zone across the wall thickness. It does not seal the wall from water vapour entirely — the wall can still breathe — but it physically prevents liquid water from climbing further.
Do You Need a Permit or a Licensed Contractor in Greece?
In Greece, cosmetic and maintenance damp-proofing of internal walls in an existing building does not generally require a building permit (oikodomiki adeia). However, if the work involves cutting into a structural wall deeper than the mortar joint, exposing foundations, or altering the external ground level or drainage, you must consult a licensed civil engineer (politikos michanikos) and may need a permit under Law 4067/2012 (New Building Regulation). Holiday rental properties registered with AADE must also maintain the structure in the condition declared on their E2 form — significant structural remediation should be documented.
For straightforward chemical injection into a non-structural internal or external leaf wall, a skilled tradesperson (waterproofing specialist — ydatosteganos) can carry out the work legally without a permit. If you are uncertain about the wall type or the extent of damage, commission a damp survey from a certified surveyor before starting.
How to Inject a Damp-Proof Course: 5 Steps
- 1
Diagnose and prepare the wall
Confirm that rising damp is the actual problem before drilling anything. Use a damp meter (hygrometer probe) to measure moisture at 150 mm, 500 mm, and 1,000 mm above floor level — readings that drop significantly as you go higher indicate rising damp rather than condensation or a plumbing leak. Once confirmed, remove any skirting boards, strip back loose plaster to at least 300 mm above the visible tide mark (the salt-stained line on the wall), and allow the wall to dry for as long as practical — ideally several weeks in summer. Drier masonry absorbs the cream more evenly and gives a better result.
- 2
Mark out and drill the injection holes
Mark a horizontal row of holes along the mortar bed joint closest to 150 mm above external ground level (or internal floor level if treating from inside). Space the holes at 120 mm centres across the full width of the wall. For a standard 230 mm solid brick or stone wall, drill each hole at a 45-degree downward angle to a depth of about 75% of the wall thickness — typically 165–170 mm — using a 12 mm masonry bit on a hammer drill. For a cavity wall, treat each leaf separately with shallower holes. Keep your drill perpendicular to the wall face on the horizontal plane so that the holes are evenly spaced and straight. Blow dust out of each hole with a rubber bulb blower or a short burst of compressed air.
- 3
Inject the damp-proof cream
Load a standard sealant gun or the proprietary injection gun supplied with your product (brands such as Dryzone, Twistfix, or Sika SikaMur are widely available in Greece through building materials merchants). Insert the nozzle fully to the back of the hole and squeeze the trigger steadily, withdrawing the nozzle slowly as the cream fills from the bottom up. The hole should be completely filled, with the cream just visible at the surface. Work along the row, filling every hole. On hot Greek summer days, work in the shade or early morning — cream that heats above 35°C before it enters the wall can start to skin over and fill less evenly. One 310 ml cartridge typically treats four to five holes in a 230 mm wall.
- 4
Allow the cream to cure, then re-plaster with a salt-resistant mix
Leave the injected wall untouched for a minimum of 24 hours (48 hours in cooler or humid weather). Do not apply plaster until the cream has fully polymerised. Re-plaster using a renovating plaster or a hydraulic lime-based mix with a pozzolanic additive — ordinary gypsum plaster applied over a previously damp wall will blister and blow off as residual salts in the masonry migrate outward during the drying-out period, which can take six months to two years in thick stone walls. Apply the first coat (scratch coat) to a maximum 11 mm thickness, let it harden, then apply the finish coat. Keep the re-plastered area damp-cured (light misting) for three days if using lime plaster.
- 5
Manage the external ground level and drainage
A chemical DPC will fail prematurely if the external ground level remains higher than the injection zone, because water will simply bypass the barrier. After the internal work is done, check that soil, paving, or render on the outside is at least 150 mm below the DPC line. If the ground level cannot be lowered (common with shared courtyards or paved streets in Greek town centres), install a French drain or channel drain parallel to the wall to divert surface water away from the foundation. Also check and clear any blocked gutters, downpipes, or surface drains near the affected wall — keeping bulk water away from the base of the building is as important as the chemical treatment itself.
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FAQ
- Can I inject a damp-proof course myself, or do I need a professional?
- Chemical DPC injection is within the skill range of a competent DIYer for a standard solid brick or concrete-block wall: the tools are inexpensive, the materials are widely available, and the process is straightforward if you follow the spacing and depth guidelines. However, you should hire a certified waterproofing specialist for thick rubble stone walls (common in older Greek island and mainland village buildings), walls with structural cracks, or any situation where you are unsure of the wall construction — incorrect hole depth in a rubble wall can miss the mortar layer entirely and waste both money and time.
- How long does a chemical DPC last?
- A correctly installed silane or silicone cream DPC typically carries a manufacturer's guarantee of 20 to 30 years, and independent testing suggests the barrier can remain effective indefinitely in walls that stay structurally sound. The most common causes of early failure are insufficient hole depth or spacing (leaving gaps in the barrier), re-plastering with salt-sensitive gypsum too soon, or a high external ground level bridging the treatment zone — all of which are preventable.
- How do I tell the difference between rising damp and condensation in a Greek climate?
- Rising damp produces a distinct horizontal tide mark (usually with white salt efflorescence) that rarely climbs higher than 1.0–1.5 m above floor level, and moisture readings are consistently highest at the base of the wall. Condensation, far more common in Greece than northern Europe, appears mainly on cold external walls and in corners at ceiling level, is seasonal (worse in winter and after rains), and is not accompanied by salt staining. A damp meter with a surface probe will show high surface readings with condensation but normal deeper-wall readings; with rising damp the deep probe reads as high as the surface probe.