York rendering guide
Why gutters and sills should be checked before rendering
Render often fails where water is delivered to it: below a leaking gutter joint, beside a dripping downpipe, under a sill with no drip. Repairing the render without fixing the water source means doing it again. Checking the rainwater goods and sills first is the simplest part of any render job, and often the most important.
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A mark shows where, not why
A stain below a sill makes the sill relevant, but it does not prove the sill is at fault; a wider photograph may show a gutter joint above it or an old repair crossing the same area. A mark that comes back after repainting shows that the wall got wet again, not why. Treat each mark as a pointer for the survey before repair, not as a diagnosis.
Patterns help. A vertical stripe usually follows a pipe or a leaking joint. A wedge spreading from under a sill follows the sill. A band along the bottom of the wall points to the base detail or the ground level. Photograph the marks after rain and in dry weather, from the same spot, so the survey can see how they change.
What goes wrong with gutters and downpipes
SPAB's guidance on rainwater fittings lists the usual faults. Gutters fracture where their bolt fixings rust; downpipes leak at joints, especially where blockages speed corrosion; gutters, downpipes and gullies block with leaves, moss and debris; and blocked gullies can lead to water building up at the foot of the wall. Externally, it notes, masonry can suffer from algae growth and eroded joints.
On render, the effect is local failure. SPAB says render may fail locally, particularly inappropriate cement-based coverings that draw moisture in through hairline cracks. It recommends regular clearing, particularly after the autumn leaf fall, checking fittings for leaks in heavy rain, and, where visually acceptable, overflow pipes above hopper heads.
Sills, ledges and the base of the wall
A sill should project from the wall with a drip underneath so that water falls clear. Old stone sills may have a groove or throat beneath for this; new sills in render systems need a drip of at least 40mm, according to K Rend's detailing sheet. A sill that has lost its drip, or one rendered over, sends water back onto the wall below.
At the base, render should stop above the damp-proof course and must not bridge it, with the DPC projecting past the face of the render. Ground, paving or planting built up against the wall above that level keeps the base wet whatever the render. Check both before the render is specified.
Parapets, valleys and hoppers
Hidden gutters cause some of the worst damage because their leaks are out of sight. SPAB notes that water from failed parapet gutters can rot concealed timbers such as roof truss bearings, and advises clearing snow from parapet and valley gutters so melt water does not seep through the joints. On a terrace with a parapet, the render below a leaking parapet gutter may be the first visible sign.
Hoppers collect water from several pipes and overflow when the downpipe below them blocks. SPAB suggests overflow pipes above hopper heads where they are visually acceptable, so that a blockage shows itself as a visible spout rather than a soaked wall. Look up at each hopper during heavy rain.
The right order of work
IHBC is clear that defective rainwater goods must be remedied before render is repaired, and the Energy Saving Trust gives the same advice before external insulation: repair roofs, gutters and downpipes first. In practice that means the roofline or gutter work is done, or at least scheduled, before the render, and the renderer knows the final position of every pipe.
If a downpipe is to be moved or replaced, agree who removes it, who fills the old fixing holes and who refixes it after rendering. K Rend recommends stainless steel brackets on rendered walls, because rust from cheap brackets stains the finish. Seal new fixings so they do not let water behind the render.
Letting the wall dry
A wall that has been soaked by a leaking gutter for years may be wet well beyond the visible stain. SPAB advises delaying re-rendering to allow drying out where the underlying fabric is saturated. There is no fixed waiting time; it depends on the wall, the weather and how long it was wet.
For example, on a hypothetical brick terrace where a cracked gutter joint has soaked the corner for several winters, the sequence might be: replace the gutter section, strip the hollow render below, leave the brick to dry while other work goes on, then re-render the corner in a material that suits the wall. Rendering straight over the wet corner would trap the moisture behind the new coat.
Repairing the render once the leak is fixed
With the water source dealt with and the wall dried, the damaged render can be repaired. Where only a strip below the old leak is hollow, a patch cut back to sound render is enough; where the whole corner has failed, renewing that face may be better. The material should match the wall: lime on a lime-rendered wall, as IHBC insists, and a compatible modern render on a modern one.
The repair will probably show at first against older render. On a painted or limewashed wall, redecorating the whole elevation once the patch has cured is the usual way to make it disappear.
Afterwards
Keep the rainwater goods working. Clear gutters after the leaves fall, look at downpipe joints during heavy rain and watch for new stains below fittings. A new stain on fresh render is a reason to check the fitting above, not to repaint.
Keep photographs of the repaired gutter, pipe positions and any changed details with the render specification. The York rendering guide separates repair, replacement and colour-change work once the water source has been dealt with.
Common questions
Should the renderer repair the gutters too?
Not necessarily; it is often a separate trade. What matters is that someone is responsible for it and that it is done, or scheduled, before the render is repaired.
How can I help if the mark is not visible during the survey?
Send dated photographs taken after rain and in dry weather, from the same position, with a note of where water was seen running. Avoid climbing to inspect gutters yourself.
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