Glass aggregate in pool finishes: how it looks and how to specify it

Last updated: 26 October 2026

Why glass aggregate looks matt when dry and glows under water, and what to check before you specify a glass pool finish: colour, slip resistance, batch planning, alkali–silica reaction and recycled-content documentation.

Glass aggregate gives a cement-based pool finish depth and sparkle under water. Particles that look pale and matt on a dry sample generally look clearer, deeper and more luminous once the pool is filled. To choose a glass finish well, view samples wet and under water and check whether the project requires a slip-resistance classification. Agree batch planning, approve an on-site mock-up as the reference, and ask the supplier for the documentation your project needs.

Why glass looks matt when dry and glows under water

Refractive index describes how strongly a material bends light. Approximate values are 1.00 for air, 1.33 for water and 1.52 for glass. When light meets a smooth boundary between two materials, more of it is reflected as the difference in index grows. Rough facets and edges also scatter light.

• Dry: the difference between glass and air is about 0.52. Facets, fine scratches and fractured edges scatter white light back towards you, so the particle looks frosted. A smooth glass–air surface reflects roughly 4% of the light that strikes it head-on.
• Under water: the difference falls to about 0.19. A smooth glass–water surface reflects roughly 0.4% of head-on light, about a tenth as much. In effect, the water fills in fine surface roughness. More light enters the particle, picks up its colour and comes back from inside it and from the background behind it.

The result is depth, stronger colour and sparkle as ripples move sunlight across the floor. In practice, a dry sample on a meeting-room table understates the finished pool. Splash-zone steps, and any waterline or overflow lip where the project specification carries the finish into a zone that spends part of its time dry or damp, will sometimes look frosted, as a dry sample does. The Technical Data Sheet treats coping and surfaces outside the waterline as needing a separate project specification.

How glass colour and base colour shape the water

Apparent water colour depends on the finish, depth, lighting, viewing angle and surroundings. Water absorbs the red end of the spectrum, more so as depth increases, and the floor and walls reflect light back. Glass particles add colour and sparkle, and the visible background colour also contributes to the appearance.

• Light base with pale, clear or blue glass: generally lighter, brighter blue water.
• Dark base (black, graphite, deep blue): deeper, more saturated tones, with stronger reflections of the sky and surroundings.
• Warm or sand bases: tend to move the water towards turquoise or green.
• Depth: shallow steps and ledges look lighter and show individual particles. The deep floor looks cooler and more saturated.

Strong tropical sun, shade from planting and underwater lighting at night all change the effect. View each shortlisted sample dry, wet and fully submerged, in sun and in shade. Compare it with completed pools of similar depth where you can. Use a physical sample and an on-site mock-up as your reference, not images on a screen.

Glass crystals and glass beads: distinct aggregate types

“Glass” in a pool finish can mean different aggregates. In the PebbleCrete range:

• The Ice colours of PebbleCrete Classic use glass crystals. They give an icy, crystalline sparkle within a mineral-looking finish.
• PebbleCrete Glass uses glass beads as its aggregate. It gives a glass-bead surface with a distinctive response to light, and its colour changes noticeably with depth and sun.
• PebbleCrete Supreme is built on glass beads, combined with natural aggregate and glass crystals.

Keep “glass crystals” and “glass beads” separate in sample requests, quotations and orders. A Classic finish with glass crystals is not PebbleCrete Glass. The families have different characters and are not ranked. Look at physical samples of each before you decide.

Smoothness underfoot and slip resistance

Pool surfaces are used barefoot, so agree acceptance criteria for the barefoot zones before work starts. The product alone does not decide smoothness or grip. Workmanship and the finished texture also matter. Check the wet mock-up by hand and with bare feet for comfort, and assess slip resistance separately.

Smoothness and slip resistance are separate requirements. In many markets, slip resistance in barefoot wet areas is assessed with the inclined-platform method in EN 16165 Annex A, and results are given as a class. Which class you need depends on national rules and the project specification. Requirements often differ by zone, so the project designer should set them for steps, ladders, shallow or beach entries and the pool floor. Where the rules require a class, confirm whether test evidence exists for that exact surface. Check that any report names the method, the surface tested (product, colour and finish) and the limits of the result.

Colour consistency between batches

Natural stone and glass applied by hand will vary slightly between batches and between pools. Slight variation is normal and is not in itself a defect. Assess it against the approved sample and the agreed acceptance criteria, and investigate any pronounced irregularities. On a large hotel pool or lagoon, clear water shows up differences quickly. PebbleCrete colour is batched to order, so plan ahead:

• Measure the actual finish area: floors, walls, steps and benches, not just the water-surface area. As a planning figure, one 25 kg bag covers about 1.8 m² at the nominal 10 mm thickness.
• Discuss batch planning with the supplier and the applicator before the application visit.
• Approve an on-site mock-up and keep the approved sample as the reference for acceptance.
• Record material and batch details in the handover documents.

Alkali–silica reaction

Alkali–silica reaction is a recognised topic in concrete technology wherever glass is combined with cement. For a thin decorative finish the relevant question is the specific product and blend, so ask the supplier what its technical documents say about it for the product you are specifying.

Recycled content

Do not assume that glass aggregate is recycled. If recycled content matters for a green-building rating, ask the supplier what documentation is available and whether the figure refers to the aggregate or the whole finish.

Questions to put to the supplier

• If recycled content matters for the project, what documentation is available, and does the figure refer to the aggregate or the whole finish?
• How will batches be planned to limit visible variation across the pool?
• What acceptance criteria apply to the surface in barefoot zones?
• What do the technical documents say about alkali–silica reaction for this product and blend?
• Where the project requires a slip-resistance class, is there test evidence for this exact surface?
• Can we see samples dry, wet and submerged? Can we see photographs of completed pools, or visit one where access can be arranged?

What glass does not change

A glass finish is decorative. It does not replace structural repair or waterproofing, so the shell, render, waterproofing and water testing each need their own agreed scope. PebbleCrete supplies the material. Unless agreed otherwise in writing, the application, the mock-up and the finished result are the responsibility of the owner and their applicator.

Care is the same across all three PebbleCrete families. Keep pH at 7.6–7.8, never add chlorine directly onto the finish, and follow the current start-up programme.

Frequently asked questions

Photographs and screen colours are illustrations. Confirm colour and texture with a current physical sample viewed wet and an approved on-site mock-up.

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This article provides general technical guidance, not a design, installation or safety instruction for a specific pool. Every project depends on its structure, substrate, waterproofing, water conditions and local regulations. Refer to the current PebbleCrete technical documents: the Technical Data Sheet and the Installation Overview are available online, and the Safety Data Sheet and the full Method Statement are issued on request. Confirm structural, waterproofing, electrical and installation decisions with qualified professionals. PebbleCrete supplies the material only; unless agreed otherwise in writing, substrate preparation and application are carried out by the owner’s applicator, who is responsible for that work. Nothing in this article limits your statutory rights.