Domakihub How to Install a Damp-Proof Membrane the Right Way
Stop rising damp before it wrecks your floors, walls, and health.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 6 min read
Damp is one of the most destructive — and most common — problems in Greek properties, whether you own a stone village house, a holiday rental on a humid island, or a basement flat in Athens. A damp-proof membrane (DPM) creates a chemical or physical barrier that stops ground moisture from migrating upward into concrete slabs and subfloors. The video above walks through the application process; the steps below give you the full picture so you can prepare the job correctly, choose the right product, and know when a licensed contractor is the safer call.
What Is a Damp-Proof Membrane and Why Does It Matter?
A DPM is a low-permeability layer — either a liquid coating or a thick polythene sheet — placed between a concrete subfloor and any floor finish (tile, wood, screed). Its job is to block capillary action: the slow upward movement of groundwater through porous concrete that causes mould, efflorescence, rotting timber, and adhesive failures. In older Greek construction, many ground-floor slabs were poured without any DPM at all, making retrofitting a critical upgrade before relaying floors.
There are two main types. Liquid DPMs (epoxy or bitumen-modified emulsions) are brush- or roller-applied directly onto clean concrete and cure to a continuous waterproof film. Sheet DPMs (heavy-duty 1,200-gauge polythene or proprietary dimple-mat membranes) are laid over the slab and lapped up the walls. Liquid products are generally preferred for renovation work because they add almost no floor height and bond directly to irregular surfaces.
When You Need a Licensed Professional or Building Permit
Installing a standard floor-level liquid or sheet DPM on an existing slab is a DIY-capable or trade job that does not require a building permit in Greece. However, several related scenarios do require qualified involvement. If rising damp is affecting structural walls — especially load-bearing stone masonry — you need a licensed civil engineer (πολιτικός μηχανικός) to assess structural integrity and specify a remedial system; wall injection damp-proofing goes beyond a simple membrane application. Basement tanking (full waterproofing of below-grade spaces) is a specialist system involving drainage channels, sump pumps, and rendered cavity membranes — it should always be specified and overseen by a waterproofing contractor certified to the relevant EN standards.
If your property is listed or in an archaeological zone, any ground-break or significant wall intervention may require a permit from the local ephorate of antiquities. When in doubt, a one-hour consultation with a structural engineer before you buy materials will save weeks of rework.
How to Install a Liquid DPM on a Concrete Subfloor (5 Steps)
- 1
Assess moisture levels and prepare the slab
Before applying any product, confirm you actually have a rising-damp problem and not a condensation problem — they need different solutions. A simple test: tape a 30 cm square of polythene to the slab with duct tape and leave it for 48 hours. If moisture appears on the underside, the damp is coming from below and a DPM is the correct fix. Next, mechanically grind or scarify the concrete to remove laitance (the weak surface layer), any old adhesive residue, paint, oil stains, or loose material. The surface must be structurally sound, dust-free, and open-pored so the DPM can bond properly. Fill any cracks wider than 0.5 mm with a suitable epoxy filler and allow it to cure fully before continuing.
- 2
Prime the surface if required
Many liquid DPM systems — particularly two-part epoxy products — require a dedicated primer to seal the concrete surface and improve adhesion. Read the technical data sheet for your specific product; skipping this step is one of the most common causes of DPM failure. Apply the primer with a short-pile roller or stiff brush, working it into the concrete surface. Allow the primer to become touch-dry (typically 1–4 hours depending on temperature and humidity) before applying the DPM coat. Note that in the warm, humid Greek summer, cure times can shift — follow the manufacturer's temperature-adjusted guidance rather than the headline figures.
- 3
Apply the first coat of liquid DPM
Stir or mix the DPM according to the manufacturer's instructions — two-part products must be combined in the correct ratio and mixed for the specified time. Pour a manageable quantity onto the primed slab and spread it evenly using a short-pile roller for open areas and a brush for edges and the junction where the floor meets the wall. Apply the membrane in one direction only on the first coat. Lap the membrane up the wall by at least 100 mm (10 cm) all around the room perimeter — this upstand is critical; any gap here creates a path for moisture to bypass the floor barrier entirely. Allow the first coat to cure to a tack-free state — usually 2–4 hours at 20°C.
- 4
Apply the second coat at right angles
A single coat of liquid DPM is rarely sufficient for a proper barrier, especially on high-moisture slabs. Apply a second coat at 90 degrees to the first — this cross-hatching technique eliminates pin-holes and thin spots that can remain invisible after one application. Use the same roller and brush technique and maintain the 100 mm wall upstand. Some high-build products allow a single thick coat; confirm this against the technical data sheet and ensure the wet-film thickness specified is actually achieved — use a wet-film gauge if you are in doubt. Total dry-film thickness for most systems should be 0.5 mm or greater. Allow the second coat to cure for the manufacturer's stated full-cure period before applying any screed, adhesive, or floor finish on top.
- 5
Inspect, protect, and proceed with the floor finish
Once fully cured, inspect the entire surface under raking light for any shiny thin spots, bubbles, or areas where the membrane appears to have been disrupted. Touch-up any suspect areas with a brush-applied patch of DPM and allow to re-cure. Protect the cured membrane from foot traffic damage by laying hardboard or ply protection sheets before other trades move through. When you are ready to lay the floor finish, use an adhesive that is compatible with the DPM — not all tile adhesives bond well to an epoxy surface. If applying a self-levelling compound, confirm in writing with the compound manufacturer that it is approved for use over the specific DPM you have chosen. Document the product, batch numbers, and application date — useful for warranty claims and building records.
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FAQ
- Can I install a DPM over a damp concrete floor, or does it need to be dry first?
- It depends on the product. Standard bitumen-emulsion DPMs require the concrete to be surface-dry and typically cannot tolerate relative humidity above 75%. Two-part epoxy DPMs are specifically formulated to be applied over damp — sometimes even wet — concrete, which makes them the better choice for renovation projects in Greece where the slab may have been drawing moisture for years. Always check the product's stated tolerance for moisture content (measured in kg/m²/24h using a calcium chloride test) and match it to your slab's actual readings.
- How thick does a polythene sheet DPM need to be?
- British and European standards specify a minimum of 300 microns (approximately 1,200 gauge) for polythene sheet DPMs used under concrete slabs. For renovation use over an existing slab before relaying a screed, 500-micron (2,000 gauge) reinforced polythene or a proprietary dimple-mat membrane gives better puncture resistance. Sheets must be lapped by at least 150 mm at all joints and sealed with the manufacturer's tape — untaped laps are a common source of failure. The sheet must also be turned up the walls by at least 150 mm and trimmed flush after the screed is laid.
- Is rising damp the same as penetrating damp, and does a DPM fix both?
- They are different problems and a floor DPM only addresses rising damp (moisture travelling upward through the ground into the structure). Penetrating damp enters horizontally through walls, roofs, or cracks from driven rain or water ingress — it requires different remedies such as external waterproofing, repointing, crack injection, or improving roof drainage. If your walls show damp patches above floor level that worsen only after heavy rain, you likely have penetrating damp, and laying a floor membrane will not solve it. A qualified surveyor or damp specialist can confirm the source before you commit to a solution.