🧱 Polyurethane Foam
It is an excellent insulator, but when it dries it becomes completely hard and rigid. With the constant expansion and contraction of the aluminium, the foam breaks, wears and detaches from the frame, letting air pass through.
Self-Expanding Tapes (Compriband): Perfect Airtightness
In construction, when you join two completely different materials (e.g. the aluminium of a window with the acrylic render of a thermal facade), there is an inviolable law of physics: materials move differently.
In summer, aluminium heats up and expands significantly. In winter it contracts. The render next to it has completely different tolerances. This constant micro-movement torments the joint that connects them.
1. The Failure of Silicone and Simple Foam
The traditional solution for sealing this gap is silicone, acrylic fillers or simple polyurethane foam.
🔧 Silicone / Mastic
Initially elastic and looks wonderful. But after 2-3 years of exposure to the hot Greek sun (UV radiation) and frost, it dries, "cracks" and detaches, leaving a hairline gap. Through that gap, rainwater will enter directly into your insulation.
2. The Compriband Revolution
The solution comes from Northern European countries (where airtightness is a religion) and is called Self-Expanding Tape (Compriband).
It looks like a roll of black, soft sponge. In reality, it is a special polyurethane foam impregnated with acrylic resins, which has been compressed very tightly in the factory.
How does it work? The worker unrolls the tape and sticks it around the window frame (like adhesive tape), just before installing the insulation or before screwing the window to the wall. At that moment, the tape is only 2mm thick. But as soon as it contacts the air, it slowly begins to expand (self-expand). Within a few hours, it has tightly filled every gap between the window and the wall!
3. The 3 Magic Advantages
🔄 Permanent Elasticity
The Compriband tape never dries out. It works like a "spring". If the aluminium expands and the gap shrinks, the tape compresses. If it contracts and the gap widens, the tape expands more to fill it! The joint stays 100% sealed at all times.
🌧️ Rain-Proof yet Breathable
It is designed to withstand driving rain at hurricane pressure. Simultaneously, like roof membranes, it allows water vapour to escape outward.
💨 Perfect Airtightness
It completely blocks cold air drafts (blow-door test), ensuring that heat stays inside.
4. The 10x10 Model Experiment
A freezing, strong north wind is blowing and it is pouring. The living-room window takes the full brunt of the weather.
❌ Scenario A (Sealed with Silicone)
After 4 summers, the silicone around the window has small, invisible cracks. The wind battering the house finds the gap, forces pressure inside and creates a cold draft (you feel "draughts" even though the window is closed). Rainwater infiltrates behind the render.
✅ Scenario B (Using Compriband)
The worker had applied self-expanding tape at the junction. The tape has "hugged" the render. No matter how hard the wind blows, the air finds no path. Water hits the tape and is repelled. The house is a perfectly sealed, warm capsule.
The Final Conclusion: A self-expanding tape costs just a few euros per metre. Yet it is the difference between a renovation that lasts 5 years (before the patching starts) and one that lives for decades. Insist that your aluminium fabricator and thermal facade installer use it on every single frame!
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Application & Construction Details: Correct Installation Guide
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