Which render system suits an exposed South Devon wall

Sand and cement render

A traditional two or three-coat sand and cement render is hard-wearing and relatively cheap, and it remains a sound choice on modern cavity-wall construction where the wall behind isn't relying on breathability. It's less forgiving of movement than lime, and on older solid walls it traps moisture that would otherwise evaporate through a more permeable finish.

Cracking is the most common failure, usually from movement in the substrate or from render applied too thick in one coat without proper curing between layers. Once cracked, cement render lets water in behind it faster than it lets it back out, accelerating damp problems rather than preventing them.

Lime render

Lime render suits solid stone, cob and older brick walls for the same reasons lime plaster suits them internally: it stays permeable and flexes with minor structural movement instead of cracking sharply. On the coast it also has the advantage of self-healing hairline cracks through continued carbonation, something cement render cannot do.

It needs a skilled hand to apply correctly, particularly around coat thickness and curing time, and it isn't compatible with modern masonry paints that would seal its surface. For conservation area and listed properties across South Devon, lime render is frequently the only appropriate specification.

Modern thin-coat and silicone renders

Silicone and acrylic thin-coat renders, usually applied over an insulated or mesh-reinforced base coat, give a wide colour range, a consistent factory-controlled finish and good crack resistance from the reinforcing mesh. They work well on new extensions and modern cavity walls where breathability isn't the priority.

They are not generally suitable as a direct replacement on solid, breathable walls without careful consideration of the whole wall build-up, since sealing a solid wall with a low-permeability system can push moisture problems elsewhere, often into the internal plaster.

Coastal exposure and detailing

Whichever system is used, detailing at junctions, window reveals and the base of the wall determines how long it lasts on an exposed elevation. Render should never be taken down to ground level without a drip detail and a gap above finished ground, since capillary rise and splashback rot the base of the render first.

On the most exposed seafront elevations, a well-detailed render with correct movement joints and bellcast details at the base will outlast an expensive system applied without them.

• Match the render's permeability to the wall's construction, not just its appearance
• Include a drip detail and clearance above ground level at the base of any render
• Use movement joints on long elevations to control where cracking occurs
• Avoid sealing a solid wall with a low-permeability finish without checking the whole wall build-up

Getting the specification right

Ask for the render system named specifically, including base coat, mesh reinforcement where used, and top coat, rather than a general description. If your wall is solid masonry, ask directly whether the proposed system is breathable and suitable for that construction.

For any coastal-facing elevation, ask what movement joint and base detailing is included, since this is where most render failures start regardless of which system is chosen.

Common questions