What is foam concrete?
Foam concrete is a lightweight type of concrete consisting of a mix of cement, water and sometimes fine sand or filler, to which a stable, preformed foam is added. The foam is made with a foaming agent and a foam generator. After mixing, countless small, closed air bubbles form in the mix. After hardening, a porous, lightweight material remains.
By varying the amount of foam, the density can vary widely, from a few hundred kilograms per cubic metre up to about 1,600 kg/m³. The lighter it is, the better it insulates, but the lower its compressive strength. When fresh, foam concrete is fluid and self-levelling, and it is usually pumped on site.
Difference with aerated concrete (autoclaved aerated concrete): in aerated concrete the pores are created by a chemical reaction (gas formation), and the material is cured in the factory under high pressure and temperature into blocks and panels. Foam concrete is poured on site and hardens like ordinary concrete.
| Foam concrete | Poured on site; hardens like ordinary concrete |
|---|---|
| Aerated concrete (autoclaved aerated concrete) | Pores created by a chemical reaction (gas formation); cured in the factory under high pressure and temperature into blocks and panels |
Application
- Raising and levelling floors: as a lightweight fill layer on old floors or under a screed, for example to embed pipes or even out height differences without adding much weight.
- Falls on flat roofs and balconies: as a light layer to create a fall (but pay attention to the roof build-up and to moisture).
- Filling voids: old pipes, cellars, tanks and underground cavities can be filled with it.
- Backfilling behind retaining walls and around foundations, where a light, free-flowing fill is wanted.
Tips and points to watch:
- Not structural without calculation: lightweight grades of foam concrete have a low compressive strength. Do not use it as a load-bearing layer without advice from a structural engineer.
- Let it dry properly: a foam concrete layer contains a lot of moisture. A screed or floor finish applied too early can cause problems. Follow the supplier’s drying times.
- Load capacity of the substrate: even a light material has weight. On a timber floor, check whether it can take the extra load.
- Have it done by a specialist: foam concrete requires specific equipment. Ask what density and compressive strength you will get.
Related Terms
- Aerated concrete
- Autoclaved aerated concrete
- Lightweight concrete
- Screed
- Levelling compound
- Retaining wall
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