About STP Extender 18

STP Extender 18 is one of the workhorse fillers in the STP Limited flooring range. On its own it is simply graded silica quartz, sorted into a coarse-to-medium band and kept clean, dry and chemically inert. Its job begins the moment it is stirred into a mixed epoxy or polyurethane binder: the resin coats every particle and locks the grains into a dense matrix, turning a thin liquid coating into a thick, trowellable screed mortar that can be laid at several millimetres in a single pass. For contractors building industrial floors, that is the difference between a decorative coating and a genuine load-bearing wear surface.

Because the aggregate carries most of the volume, a screed built with Extender 18 leans on cheap, durable quartz rather than expensive resin, which keeps the cost per square metre sensible on large slabs. The coarse-to-medium grading is deliberately matched to heavy-build systems in the 4-10 mm range, where finer sands would starve the mix of the mechanical interlock a heavy-duty floor needs. Space Arc Engineering supplies Extender 18 as an authorised STP distributor across Delhi NCR and Pan-India, alongside the STP resin binders it is designed to work with, so specifiers can source a matched screed system from a single point rather than pairing an aggregate to an unknown resin.

The technical insight

A resin floor screed is really a two-phase composite: the epoxy or PU binder is the glue, and the aggregate is the skeleton. Extender 18 supplies that skeleton. When you build a screed at 4-10 mm, you cannot get there on resin alone without cracking, excessive exotherm and runaway cost, so a high proportion of graded silica is stirred in. The coarse-to-medium particles pack together with enough void space for the binder to wet and bridge, and once cured the grains take the compressive and impact load while the thin resin films between them hold everything in shear. Abrasion resistance comes directly from the hardness of the quartz at the trafficked surface; the resin only has to keep the grains from being knocked loose. Because silica is chemically inert, it does nothing to the cure chemistry or the binder’s chemical resistance, it simply occupies volume and adds mechanical strength, which is exactly why a well-graded aggregate raises a floor’s performance rather than diluting it.

Where it is used

• Heavy-build epoxy floor screeds laid at roughly 4-10 mm in a single application
• High-aggregate polyurethane (PU) screed systems for industrial slabs
• Trowel-applied resin repair mortars for patching and re-profiling damaged concrete floors
• Broadcast aggregate over wet heavy-duty floor coatings to build a thick wear layer
• Bulking filler to convert a resin coating into a thick, load-bearing screed build-up
• Warehouse, factory and workshop floors subject to forklift and pallet-truck traffic
• Loading bays, ramps and areas exposed to dragging and impact damage
• Base build-up under a finer top coat where overall floor thickness must be raised economically

Key advantages

• Adds real thickness and body, enabling single-pass builds where a plain coating could not reach
• Coarse-to-medium grading delivers strong mechanical interlock and high compressive strength
• Excellent abrasion and impact resistance from hard quartz grains at the wearing surface
• Chemically inert, so it does not disturb the binder’s cure or its chemical resistance
• Cuts cost per square metre by replacing expensive resin volume with durable silica
• Non-toxic silicon dioxide, straightforward and safe to handle on site
• Matched to the STP resin range, giving a coherent, single-source screed system
• Consistent factory grading removes the variability of site-sourced sand

Limitations & considerations

• It is a filler component only, not a finished product; it must be combined with an epoxy or PU binder to function
• The coarse-to-medium grading is too open for fine, smooth or thin decorative finishes
• For fine anti-slip broadcasts and thinner coatings, the finer STP Extender 90 or Extender 36 is the better choice
• Must be kept clean and bone-dry before mixing; moisture or contamination compromises the bond to the resin
• Correct binder-to-aggregate ratio and thickness must follow the resin system’s own data sheet, not a fixed rule
• Final floor performance depends on the chosen binder and on substrate preparation, over which the aggregate has no influence

Selection & best practice

Specifications

Industry use cases

How we position STP Extender 18

STP Extender 18 sits at the coarse end of the STP aggregate range and is chosen when the priority is thickness and load-bearing bulk. Where a floor needs a finer surface, anti-slip broadcast or a thinner coating, step down to STP Extender 90 or Extender 36 (medium-to-fine grades), and use STP Extender 201 quartz powder where a fine, dense filler is wanted. On its own the aggregate does nothing, so pair it with an STP epoxy or PU binder such as ShaliFloor 3 ES for a chemical- and abrasion-resistant screed, or finish a build-up with a top coat like ShaliFloor TC 2 HB SF. Across our other brands, contractors who would rather buy a ready-blended, warranted screed than site-mix aggregate into loose resin can look at the Fosroc Nitoflor screed range. Space Arc can advise on and supply either route, the STP component-based system or a complete Fosroc kit, depending on the specification.

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