Most of the lime rendering we are asked about follows a failed cement render: cracked, hollow patches, damp inside and flaking paint. Putting that right is less about the top coat and more about removing what traps water and giving the wall time between coats.
Which walls actually need lime render
The rule of thumb is simple. If the wall is solid rather than a cavity, and was built with lime mortar, a lime finish suits it. That covers most Georgian, Victorian and older cottages, weatherboarded and timber-framed buildings with rendered infill, and many rural outbuildings.
Modern blockwork with a cavity does not need lime, and a sound cement render on a modern wall is usually best left alone. Knowing which you have is the first question at a site visit, and it is often answered by the thickness of the wall and the mortar in an exposed patch.
Why cement render fails on old walls
Cement is harder and less porous than the brick or stone it covers. Rain gets in through hairline cracks, then cannot dry out through the render, so it moves inwards instead. Over winters the trapped water freezes, the render lets go of the wall and sounds hollow when tapped, and the brick face behind it can crumble.
Patching a failing cement render with more cement rarely lasts. Where most of the render is hollow or the wall behind is wet, stripping back and re-rendering in lime is usually the lasting fix.
How the work is done, coat by coat
Lime rendering is slower than cement work because each coat has to firm up before the next goes on. Rushing it is the most common cause of shrinkage cracks.
- Strip any failed render and rake out loose, soft joints
- Brush down and dampen the wall so it does not suck water from the new lime
- Apply a scratch coat, keyed with a comb so the next layer grips
- Apply a float coat to straighten the wall, rubbed up as it stiffens
- Apply a thin finish coat, then limewash or a breathable mineral paint
Weather, curing time and aftercare
Lime hates frost, strong sun and drying wind while it is young. External lime work is normally planned for spring to early autumn, with hessian or sheeting hung over scaffold to keep the wall shaded and misted with water for the first days. A coat that dries too fast turns powdery and cracks.
Lime keeps hardening for months after it goes on. During that time avoid sealing it with plastic masonry paint, which would undo the point of using lime. Limewash needs renewing every few years; it is cheap to redo and keeps the surface shedding water.
Repairs versus full re-rendering
Tap the wall and mark where it sounds hollow. If the hollow areas are small and the rest is firmly bonded, cutting out and patching in matching lime is sensible. If hollow areas are widespread, or the damp inside lines up with the render, a full strip is usually better value than chasing patches for years.
Check what is causing the wet too. Blocked gutters, a raised path against the wall or a leaking downpipe will ruin new render as fast as old. Those are cheap to fix and should be sorted first.
How we approach lime render jobs
We have over 40 years of experience working on older Kent and Sussex buildings, where lime is the normal material rather than a specialist extra. Every job starts with a free site visit to look at the wall, the render and the causes of any damp, followed by a fixed-price written quote setting out what is stripped, what is repaired and how the wall is finished.
For the internal side of the same walls, see our practical guide to lime plaster on internal walls.
Common questions
Can lime render go over cement render?
Not reliably. Lime needs a porous background to grip and breathe through, so failed cement render is normally removed first.
How long does lime render take to dry?
Each coat needs days to firm up before the next, and the render keeps hardening for months. Weather has a big effect, which is why it is protected from sun, wind and frost.
Is lime render waterproof?
It is water resistant rather than waterproof. It sheds most rain and lets any moisture that does get in dry back out, which is what protects an old solid wall.
What paint goes on lime render?
Limewash or a breathable mineral paint. Plastic masonry paints trap moisture and cancel out the benefit of the lime.
Do you give a fixed price for lime rendering?
Yes. After a free site visit we provide a fixed-price written quote.