In short
- Most houses built before about 1919 have solid walls with no cavity.
- Solid walls absorb and release moisture; they need breathable renders such as lime or vapour-permeable systems.
- Hard cement render on these walls can trap moisture and damage brick, stone and timber.
- Listed buildings and conservation areas need consent for most render changes.
How to tell if your wall is solid
Look at the brick bond. Solid brick walls usually show headers, the short ends of bricks, in the pattern; cavity walls show only stretchers. Measure the wall thickness at a window or door: solid walls are often around 225 mm, cavity walls typically 270 mm or more.
Why breathability matters
A solid wall takes in some rain and some moisture from inside, then dries out through its faces. Cement render and impermeable paints slow or stop that drying. Moisture builds up, soft brick can spall in frost, timber lintels can rot and internal plaster can fail.
Options for solid walls
- Lime render and limewash: the traditional and often best option.
- Vapour-permeable modern systems: some silicone and mineral renders, specified for the substrate.
- External wall insulation with breathable materials: wood fibre or mineral wool with lime or mineral renders, designed by someone experienced in traditional buildings.
Removing old cement render
Many period houses around Surrey were cement-rendered in the twentieth century. Removing it can help the wall dry, but it can also pull off brick faces. Test a small area first.
Consents
Listed buildings need listed building consent for most render changes. Conservation areas restrict rendering an unrendered house. See planning permission for rendering.
Common problems with old cement render
On solid-walled houses rendered in cement during the twentieth century, typical signs of trouble are damp patches inside on exposed walls, flaking plaster, spalling brick where render has come away, and cracked render that holds water behind it. Timber lintels and joist ends in damp walls are at risk of decay.
Choosing the right specialist
Work on period walls needs experience with lime and traditional construction. Ask contractors for examples of lime work, what type of lime they propose and why, and how they will protect it while it cures. For listed buildings, the local conservation officer can advise, and specialist surveyors are available.
Energy improvement on older homes
Historic England's guidance supports improving energy efficiency in older buildings, provided the approach respects how the building handles moisture. Breathable insulation systems, draught-proofing and careful attention to detailing usually matter more than maximum insulation thickness. See Building Regulations for rendering.
Questions people ask
Can I use silicone render on a Victorian house?
Sometimes, if the wall is suitable and the system is vapour-permeable, but lime is often the safer choice on solid walls. Get the wall assessed.
Is external wall insulation safe on old houses?
It can be, with breathable materials and careful design. The National Audit Office found many defects in funded EWI, so quality of design and installation matters.