Recommended Stone Size & Resin Ratio for Permeable Floors

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Choosing the right stone grit size and resin-to-stone ratio is fundamental for a robust, permeable floor—especially in high-traffic areas such as plazas and terraces. The correct balance ensures optimal drainage and lasting stability.

Recommended Grit Size for Permeable Surfaces

For most outdoor resin-bound installations, including public plazas, a washed stone grit size of 4–8 mm is advised. This range allows water to pass freely through the laid surface while maintaining strength and cohesion. Stones of this size create stable layers and assist in preventing clogging, which is essential for areas with heavy foot traffic or occasional vehicle load.

Use uniform, pre-washed aggregates to ensure resin coats each stone evenly.
Combining 4–8 mm stones with finer particles can improve packing, but avoid using dust or very fine sand, which can restrict permeability.

Resin-to-Stone Ratio: Getting It Right

For white stones, aim for a resin-to-stone ratio of about 3% by weight. This means, for every 100 kg of aggregate, you should use approximately 3 kg of high-quality polyurethane binder such as Polirock. Sticking to this ratio provides lasting adhesion without oversaturating the mix, helping maintain a natural, permeable appearance. Adjustments may be needed if you’re using coloured or non-white stones or specific binders, so always consult the product guidance on your chosen resin system.

When Precise Ratios Matter Most

Following these recommendations is especially important for heavily used public areas or when using light-coloured stones (where excess resin can discolour or yellow the surface over time). Adhering to the suggested grit size and binder ratio will help prevent premature wear and maintain proper drainage—even in the face of intense footfall or exposure to the elements.

Related guides

Which Permeable Flooring Should I Install On A Plaza

By choosing the right grit size and resin-to-stone ratio, you’ll ensure your permeable flooring serves its purpose over the long term. For more detailed plaza installation tips and permeable surface options, see our plaza flooring guide.