CareHomeDeskCareHomeDeskSand-cement, anhydrite and quick-drying screeds -- which to use, how long to allow before floor finishes are applied, and what causes failures.
In care home refurbishment projects, three screed types are commonly used. Sand-cement screed (BS 8204-1) is the traditional choice -- durable, well-understood and inexpensive, but slow to dry (typically 25mm depth per week of drying time). Anhydrite (calcium sulphate) screeds dry faster than sand-cement and have excellent self-levelling properties, but must not be used in wet rooms or below DPC level. Quick-drying screeds (modified cementitious systems) allow floor finish application within 24-72 hours and are increasingly specified in care home projects to reduce programme time. All screeds must comply with BS EN 13813.
Applying a floor finish -- vinyl, tile, carpet or any adhesive-fixed product -- before the screed has dried sufficiently is the single most common cause of floor finish failure. Moisture in the screed will cause vinyl to bubble, adhesive to fail and LVT planks to lift. The acceptable moisture content at the time of floor finish application is typically 75% RH (measured using a calibrated hygrometer in accordance with BS 8201). Do not accept a contractor's assurance that the screed is 'ready' -- measure it. For critical rooms in a care home where disruption is costly, build additional drying time into the programme.
Floor screeds in wet rooms are subject to additional stresses: thermal cycling from hot shower water, cyclic wetting and drying, and mechanical impact from hoists and wheelchairs. Specify a screed with a minimum compressive strength of C25 for wet rooms. A modified screed with polymer additive provides better adhesion to the tanking membrane and better resistance to thermal cycling. If a screed in a wet room begins to crack or de-bond from the substrate, this must be investigated promptly -- the waterproof membrane beneath may be compromised. Do not simply overlay a failed screed without investigating the root cause.
CareHomeDesk gives you compliance checklists, maintenance logs, and contractor management tools built around exactly this kind of knowledge.