What is the difference between foamed concrete and normal concrete?

Normal concrete is made from cement, sand, stone aggregate and water. Foamed concrete replaces the stone aggregate with a stable foam, so it is cement, water, a pre-formed foam and usually fine sand. That single swap drives everything else: foamed concrete is far lighter, much weaker, far more fluid, self-compacting, and a much better insulator. Normal concrete carries structural load, foamed concrete fills space.

Is foam concrete better than concrete?

Neither is better, they do different jobs. Foam concrete is better where you need to fill a void, reduce load on weak ground, place material without compaction, or insulate. Normal concrete is better wherever compressive strength matters, which is most structural work. Asking which is stronger has an obvious answer, but strength is only the deciding factor when the job actually needs it.

How strong is foam concrete compared to normal concrete?

Foamed concrete typically reaches around 1 to 10 MPa in compression depending on the density specified, while structural concrete is generally in the region of 25 to 40 MPa. So a dense foamed mix might reach roughly a third of a modest structural mix at best, and a low-density mix is a fraction of that. The weakness is often deliberate, because CLSM fill is meant to be re-excavatable.

Can I use foam concrete instead of normal concrete?

Not for anything structural. Foundations, load-bearing slabs, driveways and anything relying on compressive or tensile strength need a normal mix. Substituting foamed concrete because it is lighter or flows better will produce a slab that fails under load. If flowability was the attraction, the right material is a self-compacting structural concrete, not a foamed one.

Why does foamed concrete use more water than normal concrete?

Because the foam needs it. Normal concrete typically runs a water to cement ratio around 0.4, while foamed concrete runs nearer 0.6. If a foamed mix is made too dry, the slurry is too stiff and the foam bubbles burst under the shear, which collapses the material and destroys the density it was batched to. The extra water protects the bubble structure, and it is also part of why foamed concrete sets more slowly.

Does foamed concrete insulate better than normal concrete?

Considerably better, and the lower the density the bigger the gap. The trapped air that reduces the weight also reduces thermal conductivity, so foamed concrete typically sits somewhere around 0.1 to 0.66 W/mK against roughly 0.9 to 1.4 W/mK for dense concrete. That is why it is used for insulation layers in floors and beneath roof finishes, jobs a dense mix cannot do.

Can foamed concrete be reinforced like normal concrete?

Not in the normal way. Reinforced concrete relies on a strong, dense, alkaline matrix bonding to and protecting steel reinforcement, and a lightweight cellular material with high water absorption is a poor host for that. Standard site-supplied foamed concrete should be treated as an unreinforced fill material. Structural-strength foamed concretes do exist using additional ingredients, but they are a specialist product rather than what gets delivered for void fill.

Which type of concrete is best for my job?

Work back from what the material has to do. If it carries load, take a structural mix and specify the grade. If it fills a void, reinstates a trench, reduces load on weak ground or insulates, foamed concrete is likely right and the density becomes the specification. If it needs to flow into congested reinforcement and still be structural, that is self-compacting concrete, which is a third option people often miss.

Foamed Concrete & Normal Concrete: What's the Difference?

Normal concrete and foamed concrete share a binder and almost nothing else. One is engineered to carry load, the other to fill space without being compacted, and nearly every practical difference between them follows from a single swap in the ingredients.

The One Difference Everything Else Comes From

Normal concrete is cement, sand, stone aggregate and water. The coarse stone is the structural skeleton, and it is most of why the material is both strong and heavy.

Foamed concrete takes the stone out and puts air in, held as a stable pre-formed foam. So it is cement, water, that foam, and usually a fine sand, with the lowest densities often dropping the sand too.

Remove the skeleton and the material stops being structural. Replace it with air and the material becomes light, fluid and insulating. Every row in the table below is downstream of that one change.

Side by Side

Property	Normal concrete	Foamed concrete
Coarse stone aggregate	Yes	No
Foam	No	Yes, 20% air upwards
Density	Around 2300 to 2400 kg/m3	Around 400 to 1600 kg/m3
Compressive strength	Roughly 25 to 40 MPa	Roughly 1 to 10 MPa
Water to cement ratio	Around 0.4	Around 0.6
Fluidity	Low slump, needs placing	Free flowing, self levelling
Compaction	Required, vibrated or tamped	None, self compacting
Thermal conductivity	Around 0.9 to 1.4 W/mK	Around 0.1 to 0.66 W/mK
Re-excavation	Needs breaking out	Designed to be dug out
Takes reinforcement	Yes	No, treat as unreinforced
Main role	Carrying load	Filling space, reducing load

Density in particular is a specified figure rather than a fixed property of the material. The figures above are the bands we batch and work to.

Why Foamed Concrete Needs More Water

This is the difference that gets skipped, and it explains a lot of the material's behaviour.

A structural mix wants the water to cement ratio as low as workability allows, because excess water means lower strength. Around 0.4 is typical. Foamed concrete deliberately runs wetter, nearer 0.6, and not because anyone is being careless.

The reason is the foam itself. If the base slurry is too stiff, the shear of mixing bursts the bubbles, the entrained air escapes, and the material collapses to a density well above the one it was batched to. The extra water keeps the slurry fluid enough for the bubble structure to survive intact. It also contributes to the slower set, since there is more water to lose and far less solid material conducting the reaction.

So the higher water content is not a compromise on quality, it is what makes the specified density achievable at all.

Weight, and Why It Decides Jobs

The density gap is the single most useful number here. At roughly 2300 to 2400 kg per cubic metre, normal concrete adds serious load to whatever is beneath it. Foamed concrete at 400 to 1600 kg per cubic metre can weigh less than a quarter of that at the light end.

That matters in three recurring situations: filling a void over ground that will not take more load, backfilling behind a retaining structure or bridge abutment where lateral pressure is the constraint, and adding a layer to an existing structure that was never designed for the extra weight. In all three, strength is not the question being asked. Weight is.

Placement: Compacted Versus Self Compacting

Normal concrete has to be placed and compacted, vibrated or tamped to drive out entrapped air and get it around reinforcement. Skip that and you get honeycombing and voids.

Foamed concrete is the inverse. The air is the point, so it is never vibrated. It flows into the space, finds its own level and supports itself. That is what lets it be used around live service pipework that compaction could damage, and inside voids nobody can safely enter to compact anything.

It is also why it pumps well over distance and height, which frequently decides the job where access is poor.

When Each One Is the Wrong Choice

Do not use foamed concrete for: foundations, load-bearing slabs, driveways, anything taking point loads, any trafficked wearing surface, or anything relying on reinforcement. It is not a cheaper lightweight substitute for a structural mix, and using it as one produces a failure rather than a saving.

Do not use normal concrete for: filling a void you cannot get a compactor into, backfilling around fragile service pipework, any application where the load on the ground below is the binding constraint, an insulation layer, or a trench that somebody will need to re-excavate. A full-strength backfill in a utility trench is a problem handed to whoever opens it next.

The Option People Miss

A lot of the time foamed concrete gets considered for the wrong reason: someone wants a material that flows into an awkward space without compaction, and assumes lightweight is the way to get it.

If the element is structural, the material you actually want is self-compacting concrete. It flows and self-levels like foamed concrete, but keeps the coarse aggregate and full structural strength. Foamed concrete gives up strength to gain flow. Self-compacting concrete gets the flow without that trade, which makes it the right answer whenever load is involved.

Choosing Between Them

Work backwards from what the material has to do:

Carries load? Normal structural concrete, and specify the grade.
Carries load and has to flow into congested reinforcement? Self-compacting concrete.
Fills a void, reinstates a trench, reduces load or insulates? Foamed concrete, and the density becomes the specification.

For more on the material itself, see what foamed concrete is and how it is made, the uses and benefits in detail, and the honest disadvantages. If you know the grade you need on the structural side, our concrete grades and strengths guide covers that, and the concrete calculator will convert your dimensions into a volume.

We supply both. Foamed concrete batched on site to your specified density, and ready-mix and volumetric concrete across the grades. Tell us what the material has to do on 0800 001 6147 and we will tell you which one you want, including when the answer is the cheaper of the two.