Resin Bound Paving Guide: SUDS-Compliant Aggregate Choice, Primer, Mix Ratios, Depth and UV Stability

Summary

Resin bound paving has grown rapidly in the UK market since the late 2000s, driven by two factors: the introduction of planning restrictions on impermeable driveways (see suds regulations driveways) and consumer demand for a low-maintenance, attractive surface that avoids the movement problems of loose gravel. It is genuinely permeable — water passes through the bound aggregate matrix to the base layer below — which means it satisfies SuDS requirements and doesn't require householder planning permission when used as a front driveway.

Getting it right requires attention at every stage. The base must be stable and permeable (usually existing or new porous asphalt, or an open-graded sub-base system). The aggregate must be genuinely dry before mixing — even small amounts of moisture contaminate the resin and cause delamination. The resin must be aliphatic (UV-stable) for outdoor use. And the mix must be applied at the correct depth with the right tools.

Failures in resin bound paving almost always trace back to one of four issues: damp aggregate, wrong base type, incorrect mix ratio, or use of an aromatic resin that yellows in UV. Understanding each failure mode lets you prevent them on installation and diagnose them if problems appear later.

Key Facts

• Permeable — Water passes through the aggregate void structure; voids typically 15–25% of total volume; SUDS-compliant
• Two main resin types — Polyurethane (PU, most common) and epoxy; PU is flexible and UV-stable (aliphatic type); epoxy is harder but can crack with ground movement
• Aliphatic vs aromatic — Aliphatic PU resins are UV-stable and do not yellow outdoors; aromatic PU resins are cheaper but yellow within 6–12 months in sunlight; always specify aliphatic for external use
• Aggregate sizing — 1–3mm gives fine texture and tighter appearance; 2–5mm gives more open texture; 3–6mm is less common but used for thicker applications
• Depth range — 15mm for pedestrian areas (footpaths, patios); 18mm minimum for residential driveways; 22–25mm for heavier use or frost-prone areas
• Mix ratio — Typically 1.5–2.5kg of resin per 10kg of aggregate; supplier-specific, must be followed exactly
• Aggregate must be dry — Kiln-dried aggregate specified; any moisture breaks the resin bond; mix must be used within 30–45 minutes of preparation (pot life)
• Base options — Permeable tarmac, open-graded (permeable) asphalt, or open-graded Type 3 sub-base in cellular confinement; dense impermeable tarmac is NOT an appropriate base for SUDS-compliant installation
• Primer requirement — Porous bases require a resin primer before the mix is applied to prevent the base absorbing resin from the mix
• Temperature limits — Do not install below 5°C or above 30°C; do not install in rain or with rain forecast within 6–8 hours of completion
• Pot life — Mixed resin cures in 30–45 minutes (temperature dependent); mixed batches must be laid and trowelled within this window
• UV stability test — Ask supplier for BS EN ISO 4892 UV exposure test results for the specific resin; colour retention after 2000 hours is the standard test

Quick Reference Table

Detailed Guidance

Base Preparation

The base is the most critical factor for long-term performance. Resin bound paving does not have structural value — the base carries all loads.

New permeable base — The ideal new installation uses an open-graded (porous) tarmac or asphalt base, designed to BS EN 13108-7 (porous asphalt), typically 50–75mm depth on a Type 3 cellular sub-base. This provides a fully SUDS-compliant system where water drains through resin bound → porous asphalt → Type 3 → ground.

Existing impermeable base — If laying over existing dense tarmac or concrete (e.g. an existing driveway being resurfaced), the installation is technically non-SUDS-compliant because water cannot drain through the base. In this situation, water permeating through the resin bound layer accumulates above the impermeable base. For small areas this may be acceptable if drainage channels are provided at edges. Check with the customer and the local planning authority about SuDS compliance.

Condition check — The existing base must be structurally sound. Any cracking, heave, or flexible areas will reflect through into the resin bound surface (reflective cracking). Repair or remove and reconstruct weak areas before applying resin.

Surface preparation — Clean the base thoroughly. Remove all moss, algae, oil, and loose material. Pressure wash and allow to dry completely. Any contamination under the resin bond causes adhesion failure.

Primer Application

A primer coat seals the base and ensures good adhesion.

For porous bases (new porous asphalt, open-graded aggregate) — Use a sealing primer that fills surface pores before the resin mix is applied. Without primer, the base absorbs resin from the mix, leaving aggregate with insufficient binder and causing early surface failure.

For impermeable bases (dense tarmac, concrete) — Use an adhesion primer. This promotes chemical bonding between the resin bound layer and the base.

Application — Prime by roller or squeegee; ensure full coverage with no missed areas. Allow primer to cure per manufacturer's instructions (typically 1–4 hours depending on temperature and product) before applying resin mix.

Mixing

Resin bound mixes must be mixed in a forced-action mixer (pan mixer or drum mixer with paddles). Do NOT hand-mix or use a normal cement mixer — insufficient mixing leaves uncoated aggregate and creates weak spots.

Procedure:

1. Weigh aggregate — must be kiln-dried (moisture content <0.2%). Recheck bags that have been stored on site; open bags can absorb moisture overnight in damp conditions
2. Weigh resin components A and B per supplier's ratio exactly; do not estimate
3. Pre-mix resin A and B together for 30 seconds in a separate bucket
4. Add premixed resin to the forced-action mixer
5. Add aggregate and mix for 30–60 seconds until all aggregate surfaces are coated — no white/uncoated stones visible
6. Transfer to barrow and apply immediately

Pot life awareness — In warm weather (>20°C), pot life shortens. On hot days, cool aggregate in shade before mixing. Never mix a batch larger than can be laid and trowelled within 30 minutes.

Laying and Trowelling

Screeds and bays — For large areas, divide into manageable bays. Pre-set screed rails at the correct depth. For driveway installations, a 15–18mm screed rail set 18mm below the desired finished level (to account for compaction under the trowel) is typical.

Laying — Pour mixed material from the barrow in a ribbon ahead of the trowel. Do not dump the full barrow in one place — it's harder to spread evenly and you lose working time.

Trowelling — Use a gauging trowel or resin bound laying trowel (flat, slightly flexible). Work in smooth overlapping strokes. Aim for a consistent 18mm compacted depth. The surface should be flat and tight with no aggregate protruding above the plane.

Tamping — Some installers use a rubber-faced float or a soft block to gently tamp the surface to even aggregate distribution. Avoid over-working — this can draw too much resin to the surface.

Joins between bays — Keep joins perpendicular to traffic direction where possible. Where bays meet at a working join, butt up the new bay tightly with no gap; both sides should be at the same depth.

Weather and Temperature

Aggregate Selection

Colour and size are the two key variables. Common aggregate choices in the UK market:

Golden Gravel / Buff — cream to golden tone; popular for traditional-looking driveways; natural flint or quartzite; 2–5mm most common Slate Blue / Welsh Slate — darker, contemporary look; 1–3mm for fine texture Silver/Ivory Quartz — light, reflective; quartz aggregate; 2–5mm; good UV stability (quartz does not discolour) Graphite/Black — charcoal gravel or black basalt; very contemporary; absorbs heat in summer Multi-colour blends — mix of two or more aggregates; creates visual interest

Aggregate hardness matters: soft limestone aggregates can crush and powder over time under vehicle tyres. Use angular, hard aggregates (granite, quartzite, flint) for driveways; limestone is acceptable for footpaths.

Frequently Asked Questions

Why has my resin bound paving gone yellow?

Aromatic polyurethane resin yellows in UV light. It happens within 6–12 months on south-facing driveways. The resin doesn't fail structurally but the colour change is unacceptable to most customers. There is no reversible treatment — the surface must be re-done with an aliphatic resin. Always confirm aliphatic resin in writing before starting work.

Can resin bound paving be laid over existing block paving?

Generally not recommended. Block paving is an uneven, flexible surface and the resin bound layer will mirror any voids or movement in the blocks. The preferred approach is to remove the block paving and reconstruct from sub-base, or lay a new tarmac base over the existing blocks and then apply resin bound over the fresh tarmac.

How long does resin bound paving last?

Well-installed resin bound paving should last 15–25 years. Key factors affecting longevity: base stability, aggregate hardness, resin quality, UV resistance, and maintenance (clearing algae before it causes staining). The main failure modes are: base movement causing cracking, potholing from vehicle loading on undersized installations, and aggregate detachment from low resin content areas.

Does resin bound paving need sealing?

No sealant is required. The resin itself is the binder and surface protection. Some installers apply a finishing sealer coat which can enhance colour and add some additional UV protection, but this is optional and does not change the permeability significantly. Avoid oil-based sealers which can break down the resin bond.

Regulations & Standards

• BS EN 13108-7 — Bituminous mixtures: material specifications; Part 7 covers porous asphalt used as a base for resin bound systems

• CIRIA C753 The SuDS Manual — Technical guidance on permeable paving systems including resin bound

• Town and Country Planning (GPDO) 2008 — Resin bound paving is permeable, therefore exempt from the 5m² impermeable driveway permission requirement (see suds regulations driveways)

• BS EN ISO 4892 — Plastics exposure to UV radiation; test standard for resin UV stability

• COSHH Regulations 2002 — Isocyanate-based resins (PU) require COSHH risk assessment; PPE including nitrile gloves, eye protection, and appropriate respiratory protection during mixing

• CIRIA SuDS Manual C753 — full SuDS design guidance including permeable paving

• Resin Bound Paving Association guidance — industry best practice

• BSI Online: BS EN 13108-7 — porous asphalt specification

• suds regulations driveways — planning permission and SuDS compliance for driveways

• resin bonded vs resin bound — key differences, SUDS status, and longevity comparison

• tarmac driveway installation — porous tarmac as a base for resin bound systems

• driveway drainage channels — edge drainage for partially permeable installations