Fibreglass Supplies Colloidal Silica, also known as fumed silica, is a premium quality additive widely used in resin systems, coatings, adhesives, and composites as a thickening and thixotropic agent. Available in various sizes, colloidal silica gives you precise control over flow, sag resistance and workability in your latest project.

Thixotropy describes the behaviour of certain materials that become less viscous and more fluid when agitated, mixed, or stressed, then return to a higher viscosity when left at rest. This property is especially valuable in resin systems, as it allows the resin to flow smoothly during application while ensuring it remains stable once applied. By controlling thixotropy, resins can adhere effectively to vertical and overhead surfaces without sagging, dripping, or running.

Adding colloidal (fumed) silica to resin formulations is one of the most effective ways to control thixotropy. It stabilises the resin, preventing unwanted movement after application and ensuring a consistent, even coating where uniformity is critical.

The quantity of colloidal silica incorporated directly influences the handling and flow properties of the resin. This allows users to fine-tune mixes to suit different projects. Its benefits are particularly noticeable when combined with other fillers such as glass bubbles or microballoons, where it enhances workability and prevents slump.

When used alongside fillers like glass bubbles or microfibres, colloidal silica imparts strong non-sag properties. This is a major advantage in applications requiring a specific shape, edge detail, or consistent thickness to be maintained throughout the curing process.

Colloidal silica also plays a key role in producing high-strength, non-sagging structural adhesives. When combined with microfibres, it creates robust, gap-filling adhesives suitable for bonding non-absorbent surfaces such as GRP (glass-reinforced plastics), where maximum strength and stability are required.

In addition to controlling flow, colloidal silica increases the hardness and durability of cured resin systems. This makes it ideal for creating hard-wearing surfaces or reinforced edges. However, users should note that this added hardness can make sanding more difficult, which is why colloidal silica is typically used sparingly in applications where smooth finishing is important.

• A thickening & thixotropic agent in various resin systems
• Controls the flow & sag characteristics of a resin
• Adheres well to vertical or overhead surfaces
• Essential for uniform coatings
• Prevents sagging or dripping of the resin
• Imparts non-sag properties to the resin system
• Great for using with other fillers like glass bubbles or microballoons
• Adjust the amount added to a resin to tailor handling & flow characteristics
• Ideal for creating hard-wearing surfaces
• Increases the hardness of the resulting material when added to the resin
• Great for bonding non-absorbent materials like glass-reinforced plastics (GRP)
• Sizes available: 12g Approximately 100ml, 70g Approximately 1 Litre, 310g Approximately 5 litres, 600g Approximately 10 Litres, 1.5kg Approximately 25 Litres & 10kg

Sanding Considerations: Colloidal silica can make the resin mix harder, so it may create difficulties during the sanding process. To address this, colloidal silica is typically added in minimal quantities when sanding is anticipated. In some cases, the increased hardness can be intentionally used to create durable edges or surfaces.

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