Water does not soak through sound render — it gets past it at a detail. The usual routes are cracks, failed sealant at window and door frames, a missing bellcast or drip bead at the base, render carried down over the damp-proof course, a defect above such as a gutter or roofline, and water trapped behind an impermeable render on a solid wall. Finding which one comes before any re-rendering.
- Render is a rain screen. It sheds water; it is not a membrane, and it was never meant to be one.
- Internal damp that appears a day or two after heavy rain is almost always penetrating damp, not rising damp.
- The entry point is frequently above the damp patch, because water runs down the back of the render before it finds a way in.
- Re-rendering over an unresolved detail hides the defect and buys roughly one winter.
What render is actually for
There is a persistent belief that render waterproofs a wall. It does not, and expecting it to is the root of most of the disappointment we see.
Render is a sacrificial weather coating. Its job is to take the driving rain, shed most of it down the face of the building, and let whatever moisture does get absorbed evaporate back out again. That last part matters: a render that stops water getting in but also stops it getting out will make a wall wetter, not drier.
So when water appears inside, the question is not whether the render has failed as a barrier. It is which detail has let water past it, and whether the wall can still dry.
The six routes water actually takes
| Route in | What you would see | What it needs |
|---|---|---|
| Cracks in the render | Damp patch roughly below a visible crack, worse after driving rain | Open out, reinforce and fill — after checking it is not movement |
| Failed sealant at frames | Damp at the corners of windows or above a door | Rake out and reseal; check the reveal detail behind |
| No bellcast or drip bead at the base | Damp at low level along a whole elevation | Fit a drip detail so water is thrown clear |
| Render bridging the damp-proof course | Tide mark inside at skirting level, all year | Cut the render back above the DPC and make good |
| A defect above — gutter, roofline, coping | A vertical stripe of staining; green growth outside | Fix the gutter or roofline first; the render may be fine |
| Impermeable render on a solid wall | Widespread damp, worst in winter, render sounds hollow | Breathable system; this is a specification problem |
Five of those six are detailing or maintenance. Only the last is really a problem with the render itself, which is why a quote to re-render the house is so often the wrong first answer.
Telling penetrating damp from the other two
Before blaming the render, it is worth being sure the water is coming from outside at all. The three kinds of damp look similar on a wall and have nothing else in common.
Penetrating damp
Localised, follows the weather, and appears or worsens a day or two after heavy rain, especially driving rain on one particular elevation. There is usually a matching defect outside, often higher up than the stain inside. This is the one that points at the render.
Condensation
Widespread rather than localised, worst in winter, concentrated on cold surfaces, in corners, behind furniture and around window reveals, and typically accompanied by black spot mould. It is a heating and ventilation problem. Re-rendering will not touch it, and insulating the outside of the wall may well improve it, which is a different job with a different justification.
Rising damp
Far rarer than the damp-proofing industry implies. It presents as a tide mark at low level, typically no more than a metre up, with salt deposits, and it does not vary much with the weather. Where it is genuine, the cause is usually a bridged or breached damp-proof course — and render carried down past the DPC is one of the commonest ways to bridge one.
Why the damp patch is not under the hole
This catches people out constantly, and it is the main reason repairs get aimed at the wrong place.
Water that gets behind render does not drop straight down the inside face. It runs down the back of the render until it meets something that stops it — a bead, a lintel, a change in the substrate, a line of mortar — and only then does it move inwards. By the time it shows on plaster it can be a metre or more below and to one side of where it entered.
The practical consequence: a survey that only looks at the wall around the damp patch will frequently miss the defect. We work upwards and outwards from the stain, checking the roofline, the gutter above, every opening on that elevation and the condition of the render across the whole face.
The damp-proof course problem
Of everything on this list, render bridging the damp-proof course is the one that causes the most damage for the smallest apparent fault.
Every house has a damp-proof course a little way up from ground level, designed to stop moisture in the ground travelling up the wall. If render is carried down across that line and onto the masonry below it, the render itself becomes a path around the barrier. Ground moisture wicks up through the render and into the wall above, continuously, regardless of the weather.
It is common, it is often decades old, and it is invisible unless somebody looks for it. The fix is to cut the render back so it stops above the damp-proof course, with a bellcast bead to throw water clear of the junction. Raised flower beds, new paving and built-up paths cause exactly the same problem and need the same treatment: lower the ground, not patch the wall.
Solid walls and the breathability trap
On a cavity wall, the cavity drains and ventilates, so a dense render on the outer leaf is reasonably forgiving. On a solid wall — most Coventry housing built before about the 1930s — there is no cavity. The wall gets damp in bad weather and dries back out through its own surface when the weather improves. That cycle is how the wall was designed to work.
Put a hard, dense cement render on that wall and you break the cycle. Water still finds its way in through cracks and at the top, because no render is perfect. It then cannot get out. The moisture accumulates behind the render, which is why you so often see cement-rendered solid walls with widespread internal damp and large areas of hollow-sounding render at the same time: the water is both the cause of the damp and the thing pushing the render off.
The answer on these walls is a vapour-permeable build-up — a lime-based system, or a breathable silicone topcoat over a suitable basecoat — so the wall can still dry. That is a specification decision made before anything is mixed, and getting it wrong is expensive to undo.
What we check, and in what order
- Inside first: where the damp is, what shape it is, whether it has a tide mark, and whether it changes with the weather or the season.
- The elevation that faces the prevailing weather, which usually fails before the sheltered ones.
- Gutters, downpipes and the roofline above the stain — the cheapest possible cause, and the most frequently overlooked.
- Every opening on that elevation: sealant, reveals, sills and whether the render was beaded at the frame or just butted up to it.
- The base of the wall: ground levels, where the damp-proof course sits, and whether the render crosses it.
- The render itself, tapped across the whole face to find debonded areas, which usually mark where water has been sitting.
- What the wall is built of, because that decides whether the existing system was ever the right one.
What it is likely to cost
Most of the fixes on this list are small. Resealing frames, fitting a drip bead, clearing a gutter or cutting render back off a damp-proof course are maintenance jobs, not rendering projects. Only the last route — the wrong system on a solid wall — involves re-rendering, and for context these are the rendering figures published across this site:
| Job | Typical Coventry guide price | Notes |
|---|---|---|
| Rendering | £40–£70 per m² | System & access dependent |
| Three-bed semi | £2,500–£5,000 | Full elevation render |
| Detached house | £9,000–£12,000 | Larger area & scaffolding |
We would far rather sell you a day of detailing work that solves the problem than an elevation of render that hides it. Every job gets a free survey and a fixed written quote.
We trace where the water is actually entering rather than quoting to re-render the wall it comes out of. Free survey, fixed written quote.
Frequently asked questions
Can render be waterproofed?
There are water-repellent treatments, and silicone render is itself hydrophobic at the surface, but nothing turns render into a membrane and you would not want it to. A wall needs to release the moisture it absorbs. Sealing a wall with an impermeable coating is one of the more reliable ways to create a damp problem, particularly on solid-wall property.
Is it the render or the gutter?
Look for a vertical stripe of staining or green growth on the wall below a gutter joint or a downpipe. That pattern means water has been running down the face of the wall rather than getting through it, and the fix is on the roofline. It is worth ruling out first because it is by far the cheapest thing on the list.
Why is only one wall of my house damp?
Almost always exposure. The elevation facing the prevailing weather takes far more driving rain than the others, so a detail that is marginal everywhere fails there first. It is a useful diagnostic: if one wall is wet and three are dry, the problem is weather getting past a detail rather than anything happening inside the house.
Should I re-render the whole house to stop damp?
Rarely the right first move. Five of the six common water routes are detailing or maintenance faults that re-rendering would simply cover over, and if the underlying issue is an impermeable system on a solid wall, re-rendering in the same material makes it worse. Find the route first, then decide.
How long before damp shows inside after rain?
Typically a day or two for penetrating damp through a wall, sometimes within hours where water is tracking down a clear path such as behind a frame. A delay of several days, or damp that appears in cold weather regardless of rain, points at condensation instead.
Does painting render stop water getting in?
A breathable masonry paint adds a little water repellency and can tidy up a tired elevation, but it does nothing about a crack, a bridged damp-proof course or a failed seal, and a non-breathable paint actively makes things worse by trapping moisture. Paint is a finish, not a repair.
Find out where the water is actually getting in
We survey the whole elevation, work upwards from the damp rather than straight at it, and tell you plainly whether this is a detailing job or a rendering one. Free survey, fixed written quote.