StyroBloc EPS foam blocks: cut-to-size and custom profiling

StyroBloc is a rigid EPS foam block built to be cut. It machines cleanly on CNC and hot-wire equipment, holds a crisp profile, and is light enough to handle and install by hand, which is why it is used for props, signage, formwork, landscaping shapes and custom packaging as well as construction fill. It is manufactured in Australia to AS 1366.3 and can contain recycled content. Grade is selected for the job, so confirm the density grade for the application.

When a project needs a shape rather than a sheet, EPS foam blocks earn their place. A block can be cut, carved, hot-wired and profiled into almost any form, then finished, coated or rendered. StyroBloc is the Foamex block product for this work.

This is the fabrication side of StyroBloc: custom-cut shapes for the trades that need a light, workable, dimensionally stable material. Its civil and road-embankment use is a separate application with its own guidance.

What StyroBloc is

StyroBloc is a rigid block of expanded polystyrene, produced by fusing pre-expanded beads with steam into a closed-cell block. It is manufactured to meet AS 1366.3 and supplied in large blocks that are cut down to the sizes and shapes a job needs.

The properties that make it useful for fabrication are consistent density, dimensional stability and low weight. It cuts cleanly, holds an edge, and does not sag or shift once shaped, so a profile machined today matches the drawing.

Sizes and grades

StyroBloc is supplied in blocks and cut down to the size and shape a job needs. Custom sizes are available on request.

Standard block dimensions

Width – 1200 mm

Length – 2400 mm to 5000 mm

Thickness – 600 mm

Compressive strength, density and design stress by grade

Two compressive figures matter, and they are not interchangeable. The figure at 10 per cent deformation is the one quoted on data sheets, tested to AS 2498.3 and set as a minimum in AS 1366.3. It is a material comparison figure, not a working load. The figure at 1 per cent deformation, tested to ASTM D1621, is the one to design to, because EPS behaves as a linear elastic material only up to around 1 per cent strain, and keeping sustained loads inside that limit is what controls long-term creep. Foamex publishes the 1 per cent values as maximums, so treat them as a ceiling rather than a guaranteed floor.

L Grade – 11 kg/m³ – 50 kPa min at 10 per cent – up to 14 kPa at 1 per cent

SL Grade – 13.5 kg/m³ – 70 kPa min at 10 per cent – up to 23 kPa at 1 per cent

S Grade – 16 kg/m³ – 85 kPa min at 10 per cent – up to 31 kPa at 1 per cent

M Grade – 19 kg/m³ – 105 kPa min at 10 per cent – up to 42 kPa at 1 per cent

H Grade – 24 kg/m³ – 135 kPa min at 10 per cent – up to 58 kPa at 1 per cent

VH Grade – 28 kg/m³ – 165 kPa min at 10 per cent – up to 60 kPa at 1 per cent

VVH 32 – 32 kg/m³ – 250 kPa min at 10 per cent – up to 63 kPa at 1 per cent

VVH 36 – 36 kg/m³ – 300 kPa min at 10 per cent – up to 65 kPa at 1 per cent

VVH 38 – 38 kg/m³ – 350 kPa min at 10 per cent – up to 70 kPa at 1 per cent

L to VH are the grades set out in AS 1366.3. VVH 32, VVH 36 and VVH 38 are Foamex grades that sit above the range the standard covers, so they are specified against the Foamex data sheet rather than against a grade letter in the standard.

StyroBloc can also be laminated where a job needs more than the standard block thickness.

Cut-to-size and custom profiling

Foamex provides CNC and hot-wire cutting, contract manufacturing and architectural services to turn StyroBloc into finished shapes. CNC cutting handles complex three-dimensional profiles; hot-wire cutting handles clean straight and curved sections at volume.

Custom-cut blocks also cut waste. Supplying a shape ready to install removes on-site cutting, offcuts and the labour that goes with them, which matters where the same profile is repeated across a job.

Where custom EPS blocks are used

• Film, television and event props, sets and theming, where a light, carvable material can be shaped and finished quickly.
• Signage and three-dimensional letters, cut to profile and coated or painted.
• Formwork and void formers for concrete, shaped to create recesses, curves and profiles in a pour.
• Landscaping and feature shapes, and custom packaging formers for protecting irregular products in transit.

Choosing the right grade

Work back from the load, not from the grade. Calculate the sustained load the piece will carry in kilopascals, then choose the grade whose 1 per cent figure sits above that load with a margin. Selecting against the 10 per cent figure produces a grade that looks more than adequate on paper and then creeps under a load it holds for months.

A worked example. Wet concrete weighs roughly 24 kN per cubic metre, so a 300 mm pour bearing on a void former imposes about 7.2 kPa before you add reinforcement, screed boards and the crew working over it. Allow for those and call it 15 kPa. S Grade, at 31 kPa at 1 per cent deformation, carries that with room to spare. L Grade, at 14 kPa, does not, even though its 10 per cent figure of 50 kPa is more than three times the load.

Two things move the choice beyond the arithmetic. Duration is the first: creep accumulates under load held for weeks or months, so a permanent load needs more margin than a load applied for an afternoon. Machined detail is the second: density affects how finely the block holds an edge, so fine detail, sharp corners and lettering usually justify a higher grade than the load alone would call for.

As a starting point, display, prop and signage work that carries nothing beyond its own weight sits at the light end, L to S. Landscaping and feature shapes generally sit mid-range. The worked example above is a shallow pour carried for a day or two; void formers under deep pours, or under load held for weeks rather than days, sit at H and above. Confirm the grade with Foamex against the actual loading for the job rather than defaulting to one grade across every use.

Fire and compliance

StyroBloc is manufactured as a flame retardant grade EPS. The fire-retardant additive is polymerised into the raw material formulation rather than applied as a surface coating, and Expanded Polystyrene Australia requires its members to use flame retardant material in all EPS manufactured for the building industry. A flame retardant grade resists ignition from small sources such as sparks, and self-extinguishes once the ignition source is removed.

That is not the same as non-combustible. EPS is a combustible material, and a flame retardant grade is not a fire rating. For props, sets and event work the distinction matters, because venues and productions commonly set their own fire requirements for materials brought on site, and a finished piece is assessed as a coated assembly rather than as bare foam. Confirm what the venue, production or building surveyor requires before you specify, and coat or treat the finished piece accordingly.

Finishing, coating and durability

StyroBloc takes a range of finishes, from hard-coat renders and protective coatings to paint systems, depending on whether the piece is display, exterior or structural. EPS beads are closed-cell, but water can travel through the spaces between the fused beads, so EPS absorbs more moisture than extruded polystyrene does. Exposed StyroBloc should be coated wherever it will see weather, wear or handling.

One material note: EPS is attacked by petroleum-based solvents, so coatings and adhesives should be checked for compatibility before use on a finished piece.