Render repairs in Scarborough

Finding the real extent

The visible crack is rarely the whole problem. Tap the render around it: sound render knocks solid, while render that has come away from the wall sounds hollow and may bulge slightly. Mark the hollow area in chalk; that, not the crack, is the size of the repair. Above ground floor, the same check needs ladders or scaffold.

Read the crack pattern too. K Rend groups render cracks into structural cracks, settlement and shrinkage cracks, stress cracks at the corners of windows and doors, and hairline cracks in the surface only. IHBC adds that long cracks running in one direction may reflect structural movement, which should be investigated before any repair. A hairline craze is cosmetic; a stepped crack through a gable may not be.

Water first, render second

Many local failures have a water source. A leaking downpipe joint, a gutter overflowing at one corner, a sill without a drip or render carried down over the damp-proof course can soak one area until it lets go. SPAB's advice on rainwater fittings notes that render may fail locally, particularly cement coverings that draw moisture in through hairline cracks.

If the cause is a fitting, have it repaired before the render. If it is the detail at the base or under a sill, the repair should change that detail: a bellcast bead so the render stops above the damp-proof course, or a sill with a proper drip, for which K Rend's detailing notes give a 40mm minimum. Patching without changing the cause usually means patching again.

How a patch is made

The damaged render is cut back to sound, well-bonded material with neat edges rather than a feathered outline. The exposed wall is brushed down and any loose brick, block or mortar repaired. The patch is then built up in coats to the thickness of the surrounding render, in a compatible material: cement-based on a modern wall, lime on a lime-rendered one.

Where cracks keep returning at window corners, mesh in the base coat across the corner helps, as it does in new work. K Rend also advises leaving an active crack as long as possible to stabilise before repair, so a crack that is still opening may need monitoring first. The finish is then worked to match the existing surface: scraped, floated, roughcast or dashed.

1. 1

   Tap-test and mark the hollow area

2. 2

   Fix the water source or change the detail

3. 3

   Cut back to sound render with clean edges

4. 4

   Repair the exposed background

5. 5

   Rebuild in coats to the existing thickness

6. 6

   Texture to match; repaint the whole face if it is painted

How close will the patch match?

A patch seldom disappears completely. The surrounding render has weathered, picked up dirt and may have been painted, while the new material starts fresh. Through-coloured renders such as monocouche can show a change of shade, whereas painted render hides a repair best because the whole elevation can be repainted afterwards. K Rend supplies a coloured filler and an evening-up coating for its own finishes for exactly this reason.

Decide in advance whether a visible patch is acceptable or whether the repair should be followed by cleaning or recolouring the elevation. The answer is often different for a front wall facing the street and a rear wall behind the yard.

Safety and older buildings

Loose render over a doorway, path or pavement can fall without warning. Keep people away from it and have it made safe; on a building beside the street, that may mean scaffold or a barrier, and scaffold on the footway needs a North Yorkshire Council licence applied for by the scaffolding company.

On an older solid wall the repair material should be lime. IHBC warns against patching weak historic lime with cement or strong hydraulic lime and recommends a matching lime instead. See lime rendering for how lime coats are built up and protected while they cure.