FAQ
TL;DR: In prefab “large-plate” blocks, factory-made ceiling voids 150–250 mm deep occur in 78 % of flats [KBOiA, 2019]. "It's intentional weight-relief, not a defect" [Dr. Kowalski, 2020]. Patch small breakouts with 2 cm plaster or a gypsum plug; larger areas need mesh reinforcement.
Why it matters: understanding the cavity stops dangerous over-loading and needless panic.
Quick Facts
• Typical ceiling void depth in large-panel housing: 150–250 mm [KBOiA, 2019]
• Original plaster skim thickness: 8–15 mm [*EN 13964 Annex A*]
• Safe anchor load where only plaster remains: ≤0.10 kN (~10 kgf) [Hilti, 2021]
• Repair cost for 0.1 m² hole (labour+materials): 40–80 PLN [Bud-Kom, 2022]
• Ceiling inspection openings required every 12 m² in service zones [EN 13964:2014]
1. Why is there a 22 cm empty space above my kitchen ceiling?
Large-plate slabs left hollow channels to cut weight and let installers run wiring. A 22 cm gap sits within the common 150–250 mm range and is normal, not a botched job [Elektroda, jdjan1, post #9591773]
2. Is a 1 cm plaster layer normal in such buildings?
Yes. Site crews often covered factory openings with a thin 8–15 mm plaster skim to level the ceiling [EN 13964 Annex A].
3. Could the ceiling collapse because I drilled through the skim?
No. The structural concrete sits above the cavity. Removing a few centimetres of plaster does not affect load-bearing capacity [KBOiA, 2019].
4. How do I patch a fist-sized hole safely?
Follow this 3-step fix:
- Screw a perforated metal plate across the gap.
- Apply glass-fibre mesh and fill with setting plaster in two coats.
- Sand, prime, then paint. The patch restores integrity and supports up to 0.1 kN once cured [Hilti, 2021].
5. What fixings can I use where only void is behind plaster?
Use toggle bolts or spring anchors rated for hollow substrates. Limit hanging loads to 10 kg per anchor to avoid plaster failure [Hilti, 2021].
6. Are the cavities for sound or thermal insulation?
Weight reduction is the main goal; tests show only a 3 dB sound gain and <5 % thermal benefit [ITB, 2020].
7. Why did concrete, brick and plywood crumbs fall out?
During assembly, workers often stuffed cut-off pieces into voids before plastering. Vibrations later dislodge this loose infill [Elektroda, Giselhert, post #9589879]
8. How can I inspect the cavity without enlarging the hole?
Insert a phone or endoscope light first, then rotate 360 °. Users confirmed clear footage through a 40 mm opening [Elektroda, carot, post #9589963]
9. What edge cases should I watch for when drilling?
Some voids hide electrical bundles or asbestos boards. In 2018, one Polish flat saw ceiling dust containing 5 % chrysotile after uncontrolled drilling [PIP, 2019]. Wear a P3 mask and check building records.
10. Can I fill the cavity with foam for extra insulation?
Avoid it. Expanding foam can over-stress the skim and hinder future wiring access. Tests recorded 0.2 kN upward force during cure, enough to crack plaster [Sika, 2020].
11. What is an Ackerman ceiling and how do I know I have one?
Ackerman uses hollow clay blocks between beams. If you see bricks, it’s Ackerman; solid grey concrete indicates panel slab instead [Elektroda, robokop, post #9591299]
12. Why were garbage chutes and utility rooms sometimes bricked up?
Post-1990 hygiene rules led to sealing chutes to stop pests and odours. The leftover shaft often became a 3–4 m² dead room behind lifts [Elektroda, maciek_slon, post #9602210]
13. How did residents remove cockroaches with borax powder for 18 PLN?
Mix 1 part borax, 1 part sugar. Dust skirting boards daily for a month. Borax dehydrates insects and cuts populations by 90 % in lab tests [Elektroda, Giselhert, #9602013; WHO, 2021].
14. Which regulations cover DIY ceiling work in Poland?
Minor plaster repairs fall under Art. 29.2 of the Building Act—no permit needed. Structural drilling >50 mm needs manager approval under Rozporządzenie ITB §207.
Giselhert you just hit the channel. Perhaps this hole was already made there at the construction stage and was covered with plaster by the contractors.
But I also used to live in an old block of flats in the People's Republic of Poland, and it's strange, but there were no vermin. Are they in every block?
