Lido & Outdoor Pool Testing

UK lido and outdoor pool stock

UK outdoor pool stock spans:

• Heritage 1930s lidos — e.g. Saltdean, Tooting Bec, Tinside, Brockwell; original concrete or terrazzo paving with listed-building status
• Inter-war and post-war municipal outdoor pools — older councils' pre-war or 1950s installations
• Hotel and resort outdoor pools — UK luxury hotel outdoor pool decks, often with newer specifications
• Holiday park pools — intensive seasonal use, often timber or modern non-slip composite decks
• Private outdoor pools — country-club and members' outdoor lap pools

The seasonal contamination cycle

Outdoor pool deck PTV is not a single annual number. The same surface can produce:

• PTV 45 in mid-summer, dry-deck conditions, swept — nominally compliant
• PTV 32 after sun-cream residue accumulation through a hot-weather day
• PTV 28 in autumn after leaf-litter deposition — moderate slip risk
• PTV 18 with algae bloom in damp shaded sections — high slip risk
• PTV 12 with surface frost (relevant for year-round outdoor pools)

Single-visit data therefore captures one snapshot. Bi-annual or seasonal testing programmes capture the variation that affects the actual operating risk.

Sun-cream residue — an underappreciated contaminant

Hot-weather lido use produces sun-cream residue accumulation on poolside paving that is rarely recognised in operational risk assessment but reliably reduces PTV. The residue concentrates where users sit, stand and walk barefoot — predictable hot-spots include the shaded areas around umbrellas and loungers, the cafe-seating-to-pool transit corridor, and the top step of pool entry. We test these zones specifically during hot-weather visits.

Heritage and listed-building constraints

UK heritage lidos typically operate under listed-building consent that constrains remediation choices:

• Original concrete and terrazzo paving cannot easily be replaced without consent
• Anti-slip chemical etching that preserves the visual finish is usually permissible
• Step-nosing improvements may be permissible where original tread surfaces are retained
• Drainage and contamination-management improvements are usually consent-free

For listed lidos, pendulum testing identifies the actual current state; the listed-building consent process determines the remediation pathway. We work with the operator's heritage consultant to scope realistic options.

Algae management as part of slip-risk control

Biological algae growth on damp shaded poolside paving is the single most consistent reducer of outdoor pool deck PTV. Operators with active algae-management programmes (biocide-cleaning regimes, sun-exposure pruning of overhanging vegetation, drainage-clearance) maintain materially better PTV than those without. The pendulum captures the result; the operational programme determines the long-run pattern.

Seasonal closure and reopening

For seasonal lidos closing in winter and reopening in summer, pendulum testing in the late-spring pre-opening period captures the surface as it has weathered through winter. This is often quite different to the late-summer end-of-season state. Two visits per season — pre-opening and end-of-season — produce the most useful data for seasonal-pool operators.