Equipment and plants

Foam concrete equipment divides into four classes that differ less in technology than in degree of automation. What they share is a foam generator and a low-shear mixing arrangement; what separates them is throughput, capital cost and how much of the process a person has to watch.

The foam generator

Every foam concrete installation has one, and its output quality sets a ceiling on everything downstream. A generator takes a diluted foaming-agent solution and compressed air and forces them together through a restriction that breaks the mixture into fine, uniform bubbles.

What a generator consists of

• Solution tank and dosing pump. Either pre-diluted solution in a tank, or an inline dosing pump metering concentrate into a water line. Inline dosing removes the most common source of variation — dilution made up by eye — and is worth the extra cost.
• Compressed air supply. Typically 4 to 8 bar. Air must be clean and dry; compressor oil carried into the foam is a classic cause of unexplained foam collapse.
• Foaming lance or cartridge. A tube packed with mesh, beads or baffles. This is the wear part and it determines bubble size.
• Flow controls and a calibration point. A tap where foam can be run into a measuring vessel for a density check.

Sizing

Rated output is quoted in cubic metres of foam per hour, commonly 10 to over 100 m³/h. Convert the placing rate into foam demand before choosing: one cubic metre of 400 kg/m³ material needs about 0.7 m³ of foam, while one cubic metre at 1200 kg/m³ needs about 0.35 m³. The low-density work is what sizes the generator. See mix design for the calculation.

Maintenance that matters

• Flush with clean water after every use. Dried foaming agent in the lance changes bubble size before it blocks anything.
• Check foam density at the start of every shift and log it. A drifting figure is the earliest warning of a worn lance or a failing dosing pump.
• Drain the air receiver and service the air dryer on schedule.
• Replace lance packing on condition, not on a fixed interval; the log tells you when.

Mobile all-in-one units

A skid, trailer or container carrying a mixer, a foam generator, a compressor and a pump, sized for site-cast work: trench reinstatement, void filling, screeds and small precast runs. Typical output is 5 to 30 m³ per shift.

Strengths. Capital cost is modest, one machine covers the whole process, and the unit goes to the material rather than the material to the unit — which matters for a product whose low value density makes long haulage uneconomic.

Limits. Batch sizes are small, so a large pour becomes a long sequence of batches with a cold joint risk between lifts. Weigh batching is often approximate, sometimes volumetric, and consistency depends on the operator. Densities below about 300 kg/m³ are hard to hold reliably on this class of equipment.

Semi-automatic plants

A fixed installation for block and panel production, with the process split into stations and manual transfer between them.

1. Storage. Cement silo with screw conveyor, sand hopper, water tank, foaming agent drum store.
2. Weigh batching and mixing. Load cells under the weigh hopper, a low-shear paddle or ribbon mixer, and a foam line entering the mixer with its own flow measurement.
3. Casting. Either individual moulds or, more commonly, large slab moulds poured in one go.
4. Cutting. Slabs are cut green — after initial set but before full hardening — with a wire cutting frame, in both directions. Timing is the skill: too early and the cut face slumps, too late and the wire tears rather than cuts.
5. Curing. Covered racks for ambient curing, or a low-pressure steam chamber where cycle time matters.
6. Packaging. Manual or semi-automatic palletising and wrapping.

Output typically runs from 30 to 150 m³ per shift. This class covers the large majority of dedicated foam concrete block production worldwide, because it is the point where the process is controlled enough to certify a product without the capital cost of full automation.

Fully automatic plants

The same stations, with material handling, dosing, casting, cutting and curing under a single control system and no manual transfer. Two configurations exist:

• Batch plants, where each mix is weighed and mixed discretely, with automated transfer between stations. Full traceability per batch.
• Continuous in-line plants, where slurry and foam are metered continuously into a static or dynamic in-line mixer and discharged straight into moulds. Higher throughput and less equipment, but density control depends entirely on the two flow meters staying calibrated — there is no batch to weigh.

Output ranges from 150 to well over 1000 m³ per shift. Automation buys consistency rather than any change in the material, and it only pays where volume is high and stable enough to service the capital.

Ready-mix integration

The lowest-capital route into foam concrete is not to build a plant at all, but to add foam to an existing ready-mix operation. Two arrangements are in use:

• Foam injected at the batching plant. A generator doses foam into the truck drum after the slurry is loaded. The load then travels as foam concrete, and the density is whatever survives the journey — which on a long haul with a rotating drum may be some way above target.
• Foam generated on site. The truck delivers a conventional slurry batched to a foam concrete recipe, and a generator at the point of placing doses foam into the discharge. More equipment on site, far better density control, and the preferred arrangement wherever the specification has a real tolerance in it.

Either way, the slurry has to be batched to a foam concrete recipe, not to a normal concrete recipe with foam added afterwards — the water content, the absence of coarse aggregate and the admixture regime are all different, and a plant superplasticiser will strip the foam.

Pump selection

Whatever the pump, verify density at the outlet, not just at the mixer. The number that matters is the one at the point of placing, and the difference between the two tells you exactly what the delivery line is costing you.

Choosing a class

Commissioning checks

Before accepting any foam concrete installation, run these and record the results. They are cheap and they establish the baseline against which later drift is measured.

1. Foam density across the operating range. Measure at minimum, nominal and maximum output. It should hold within a few g/L at every setting.
2. Foam stability. Draw a sample, leave it standing, and measure drainage over time against the agent manufacturer's figure.
3. Batch repeatability. Five consecutive identical batches; wet density should fall within ±3 % without adjustment between them.
4. Density loss through the delivery line. Measure at the mixer and at the outlet with the full line laid out at working length and height.
5. Density gradient in a deep cast. Cast a full-height section, cure it, then core or cut it and check density top to bottom. This is the test that finds foam instability, and it is the one most often skipped.
6. 28-day strength at each production density, tested to a named method with the moisture state recorded.

Last reviewed: 7 September 2026