Domakihub Inject Foam Into Existing Walls — No Demo Required
Fill uninsulated wall cavities in older Greek homes without stripping a single tile or breaking plaster.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
Millions of Greek apartments and holiday villas were built before modern insulation standards existed, leaving hollow wall cavities that bleed heat in winter and let summer heat flood in. The good news is that you can fix this without a full renovation: the drill-and-inject method pumps expanding foam directly into the cavity through small holes that are patched and painted over when the job is done. The video above shows the full process on a real house; the steps below translate that into practical guidance for homes, holiday rentals, and hotel blocks in Greece.
Why Older Greek Buildings Have This Problem
Most residential buildings constructed before the 1980s — and many built through the 1990s — were designed with cavity walls or single-wythe masonry that relied on thick render and shutters to manage the climate rather than any real thermal barrier. In a country where summer cooling costs have overtaken winter heating costs, this gap in the building envelope is a year-round energy drain.
Holiday rental owners feel this doubly: guests crank the air conditioning to compensate for heat seeping through uninsulated walls, utility bills rise, and reviews mention rooms that never feel quite comfortable. A single retrofit session with injection foam can close that loop permanently without moving furniture or evacuating the property for weeks.
What Injection Foam Actually Does
Injection foam — typically a two-component polyurethane or a water-blown tripolymer foam — is a low-expansion material specifically engineered for closed cavities. Unlike the spray foam used in open attics, it expands just enough to fill voids without warping window frames or cracking plaster. Once cured it bonds to masonry, seals air infiltration pathways, and raises the effective R-value of the wall assembly meaningfully.
Beyond thermal performance, the foam also acts as a sound barrier. In a block of flats this matters: tenants separated by a party wall that was previously an empty air column gain a noticeable reduction in neighbour noise after injection — a genuine selling point for landlords listing on short-term rental platforms.
How to Inject Foam Into Existing Walls: 5 Steps
- 1
Locate the cavity and map drill points
Use a stud finder or a simple tap-test to confirm there is an air void behind the surface. On a typical Greek external wall with a cavity, mark drill points every 40–60 cm in a horizontal row, usually about one-third of the way down from the top of each stud bay. On masonry with no internal framing, a single row of holes near the top of the wall section is often enough for the foam to flow downward by gravity and pressure.
- 2
Drill the injection holes
Fit a masonry bit sized to match your foam gun nozzle — commonly 16–22 mm. Drill at a slight downward angle so foam cannot flow back out before it cures. Keep the drill perpendicular to the wall face and go only as deep as the outer leaf of the cavity; you do not want to punch through to the interior finish on the other side. Vacuum dust from each hole before proceeding so the nozzle seals cleanly.
- 3
Inject the foam from the bottom up
Insert the nozzle fully into the lowest hole in a bay and trigger the gun steadily. You will feel back-pressure build as the cavity fills; when foam begins to appear at the hole above, that bay is full — move the nozzle up to the next hole. Work methodically across the wall rather than trying to fill large areas from one point. For two-component polyurethane, mix ratios matter: follow the manufacturer's temperature guidance, which is especially relevant in Greece where summer site temperatures can exceed 35 °C and accelerate cure time.
- 4
Allow full cure before patching
Low-expansion injection foam typically reaches handling strength in 30–60 minutes but continues to cure for several hours. Resist the temptation to patch holes immediately; if uncured foam is trapped under mortar it can push the patch out. Once cured, trim any foam that has expanded slightly proud of the hole with a utility knife, then fill with exterior-grade filler or hydraulic cement, feather smooth, and allow to dry fully before painting.
- 5
Patch, paint, and verify the seal
Match the existing render or paint finish as closely as possible — on older Greek lime-render walls a slight texture variation is normal and weathers to match within one season. Once the surface is restored, run a simple blower-door test or even a stick of incense around window reveals and electrical outlets nearby to check whether air infiltration has dropped. A thermal camera scan on a cool morning will show the treated cavities as warm, uniform patches compared with any remaining cold spots — useful documentation if you are claiming the improvement for rental marketing or an energy certificate upgrade.
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FAQ
- Will injection foam damage the existing plaster or render on my walls?
- Low-expansion injection foam is specifically formulated not to. It fills the void and stops expanding once it meets resistance. Standard two-part spray foam used in open cavities would crack plaster, but the injection-grade product sold for retrofit work exerts very little outward pressure. The main risk is drilling too close to electrical conduits or pipes hidden in the wall — always check with a detector before drilling.
- How long does the job take for a typical Greek apartment?
- A single external wall of around 20 square metres can usually be drilled, injected, and patched in one working day by a two-person crew. A full apartment perimeter with multiple facades could take two to three days. The work is largely non-invasive, so you do not need to vacate — though sealing rooms from foam odour during injection is advisable.
- Is injection foam insulation eligible for Greek energy-efficiency grants (Εξοικονομώ)?
- Retrofit insulation of the building envelope is one of the qualifying intervention categories under the Greek Εξοικονομώ (Exoikonomw) programme. Eligibility depends on the programme cycle, the energy class improvement achieved, and whether a licensed energy inspector certifies the before-and-after performance. Check the current programme terms at the PRYRE portal and get a pre-injection energy certificate so the improvement is documented and fundable.