Lime, sand and cement or silicone? Choosing render for a Wiltshire home

Render protects a wall as much as it finishes it. Choosing the wrong type for the building is one of the most common causes of damp in older Wiltshire homes. The right choice depends mainly on how the wall is built.

Older solid walls: let them breathe

Many houses in Devizes, Bath and the surrounding villages were built before cavity walls, in stone, brick or cob, with lime mortar. These walls take on some moisture and let it dry out again. Hard cement render traps that moisture, which then shows up as damp patches inside, blown plaster or crumbling stone behind the render.

Lime render is the usual answer on these buildings. It is softer, flexible and vapour-permeable, so the wall can keep drying out. It takes skill and time to apply and needs protecting from frost and fast drying while it cures. Our guide to lime mortar and repointing explains the same principle for brickwork.

If your house is listed or in a conservation area, check with Wiltshire Council before changing the external finish, as consent may be needed.

Modern cavity walls and extensions

Modern blockwork extensions and new builds are designed differently, and there are more options:

• Sand and cement. Traditional, economical and hard-wearing. Usually painted.
• Monocouche. A through-coloured render applied in one thick coat, so no painting.
• Silicone (thin coat) systems. Through-coloured, water-repellent and good at staying clean, with some flexibility.

Details that make render last

Whatever the system, beads at corners and openings, a bell-cast above the damp-proof course, and properly prepared backgrounds decide how long it lasts. Render should never bridge the damp-proof course.

Changing the look of the house

Rendering over brick or stone can need planning permission in some cases, and always in conservation areas or on listed buildings. Check before you commit.

See our plastering and rendering page for the systems we use.