Lime render, older houses
Lime Render Sheffield: Re-rendering an Older Stone House
Lime render is the traditional coating for solid stone and soft brick walls. It is softer and more open than cement render, so moisture that gets into the wall can dry back out through it. Re-rendering a whole older house in lime is slower than any modern system: the old cement often has to come off first, the wall may need to dry, and each coat needs days to cure. It is usually worth it on walls that have been suffering under the wrong render.
On this page
Why older houses end up re-rendered in lime
Many older Sheffield houses were given hard cement render or pebbledash in the twentieth century. SPAB explains the problem: impervious cement render restricts evaporation from a solid wall, and because it is more rigid than the masonry it develops hairline cracks that let rain in and then trap it. Cement renders tend to fail in patches and come away from the wall, while lime erodes slowly and evenly. Grenoside's conservation-area management proposals name walls rendered with concrete and cement repointing among the changes that weakened the village's stone buildings.
Lime is not automatically the answer for every old house. A later brick extension, or a house that was built for cement render, may be better in another system. The case for lime is strongest where the walls are solid stone or soft brick and show signs of trapped damp behind a hard coat.
- Stone or brick masonry Cleaned of loose material and dampened so it does not draw water out too fast.
- First (scratch) coat Often haired; scratched to give the next coat a key.
- Second (floating) coat Applied once the first has firmed up; follows the line of the wall.
- Finish coat Thin final coat, kept damp and shaded while it cures.
- Limewash or mineral paint Optional decoration that keeps the wall permeable.
Wall on the left, finish on the right. Not to scale: coats, thicknesses and primers follow the chosen manufacturer’s system and the condition of the wall.
Taking off the cement and letting the wall dry
SPAB's advice is to test-remove a small area first, because removal can damage soft stone or brick. Cement is knocked off carefully with hammer and chisel; levering off large sheets can pull the face off the masonry beneath. Where cement render is still firmly bonded, leaving it to weather, or removing only the hollow-sounding patches, can be the better compromise. On a whole house this usually means different decisions on different elevations.
Once stripped, a saturated wall should be left to dry for a while before re-rendering, and decayed stone or brick made sound. SPAB also warns that a new lime render can act like a poultice and draw salts out of a wall that has had cement on it for years, so some early decay at the base can follow, and a sacrificial coat may need renewing after a couple of years.
Three coats on a whole house
Cornish Lime's guide sets out the usual sequence. The wall is dampened with a sprayer, not a hose, then a bonding coat of about 9-12 mm is thrown or laid on and keyed once it has taken its initial set. After about a week in normal conditions, a straightening coat is ruled off and scored with a devil float, and finally a top coat no thicker than 5-7 mm is applied. Lime Green's guidance for its lime renders adds that the background should be misted about half an hour before rendering and not over-wetted.
Curing is where whole-house lime jobs succeed or fail. Cornish Lime calls drying too quickly the most common cause of failure: plastic shrinkage cracks show within 48 hours, and it recommends hessian hung close to the work for at least two weeks. Frost must be avoided, particularly in the first 14 days. With a week or so between coats on every elevation, a whole house in lime needs a long frost-free season, so these jobs are normally planned for spring to early autumn, with the scaffold sheeted throughout.
Trial-remove a small area of cement render on each elevation.
Strip where it is safe to do so, and let the wall dry before work continues.
Repair soft or decayed stone and brick, and fill deep voids with lime mortar and stone.
Dampen the wall and apply the bonding coat; key it after its initial set.
After about a week, apply and devil-float the straightening coat.
Apply the top coat, then keep the work under damp hessian and out of frost while it cures.
Finish with limewash rather than modern masonry paint.
Finish, permissions and Part L
SPAB recommends limewash as the usual finish because it stays open; modern masonry paints can trap moisture. Limewash weathers and is renewed every few years, which is part of owning a lime-rendered house.
Many older stone houses sit in conservation areas or, in High and Low Bradfield, the Peak District National Park, where cladding a house with render is not permitted development, so a change of finish needs the planning authority's view. Approved Document L counts re-rendering as renovation, but it also says traditional stone and lime walls should be upgraded only where that will not cause long-term deterioration, and building control will take the conservation officer's advice into account.
Common questions
How long does a whole house in lime take?
Longer than a modern system. With about a week between coats in normal conditions and curing under hessian, each elevation takes weeks rather than days, and frost stops work.
Can lime go over the existing cement render?
Not as a rule. The point of lime on a solid wall is to let moisture dry out through it, which a cement coat left underneath would prevent. Firmly bonded cement is sometimes left alone, but new lime goes onto the masonry.
See housing and planning information for Sheffield and nearby places, including the source and geography behind each figure.
