Breathable Render Systems for Heritage & Period Properties

A breathable render system is one that allows water vapour to pass through the render and out of the wall. Old buildings (stone, cob, solid brick) manage moisture by allowing it to move through the fabric and evaporate. Cement render blocks this process, trapping moisture in the wall and causing damp, spalling, and structural damage over time. A breathable lime render system replicates the original behaviour of the building materials and is essential for the long-term health of traditional buildings.

Lime-based breathable render systems typically cost more per square metre than sand-and-cement render because the materials cost more, application is more labour-intensive, and correct curing management requires more time on site. However, the cost comparison changes significantly when you account for the damage caused by inappropriate render: damp treatment, internal plasterwork, decorating, and structural repairs can far exceed the premium on a correct breathable system at the outset.

No. Lime render behaves differently from gypsum and cement-based products. It sets more slowly, requires different application techniques, and demands correct curing management. Applied incorrectly (over-wet, in frost, in direct sun, or without adequate curing time between correct curing between coats) it will fail. Riley's has extensive experience with lime render and breathable systems. We do not apply these materials casually.

Natural Hydraulic Lime (NHL) sets through a hydraulic reaction with water, producing a render that is reasonably weather-resistant during curing, suitable for the South West's wet climate. Lime putty is non-hydraulic, setting solely through carbonation (absorbing CO2 from the air). It produces the softest, most breathable, and most flexible render possible, but is slower to set and more vulnerable during curing. Lime putty is generally preferred for very soft substrates, internal work, and historic repairs. NHL is the more common choice for external heritage render in Devon and Cornwall.

For unlisted properties not in a conservation area, planning permission is not normally required to apply a breathable lime render. For listed buildings, listed building consent is required before any render is applied or removed. This is a legal requirement. For properties in conservation areas, permitted development rights may restrict certain render finishes. Riley's advises on consent requirements as part of the project assessment.

A correctly specified and applied lime render system on a suitable substrate should last 30 to 50 years with normal maintenance, which typically means periodic lime washing or breathable paint. The lifespan depends heavily on the quality of the substrate preparation, the accuracy of the specification, application conditions, and the building's exposure to the elements. Properties in coastal Devon and Cornwall face more demanding conditions than sheltered inland buildings.