Cracked render is one of the most common problems we see on homes across Pontypridd and the Valleys, and the wet Welsh climate means it rarely improves on its own. The good news is that most cracks are repairable, and some are a straightforward weekend job. The key is knowing which type of crack you are dealing with before you reach for the filler.
Render cracks for a handful of reasons, and the fix depends on the cause. In South Wales the biggest culprit is freeze-thaw damage: rainwater gets into a tiny crack, freezes over winter, expands, and forces the crack wider year after year. With over 1,400mm of rain falling annually in parts of Rhondda Cynon Taf, render here works harder than it does in drier parts of the UK.
Other common causes include a strong sand and cement render applied over soft old brick or stone, which is typical on Victorian terraces and cannot flex with the building. You will also see cracking from failed pebbledash, blocked or leaking gutters soaking one section of wall, and normal settlement around windows and doors. If the crack follows a stepped, staircase pattern through the render, that can point to movement in the wall itself rather than a render problem.
As a rough rule, hairline cracks under about 0.5mm wide are usually cosmetic surface crazing. Cracks between roughly 1mm and 5mm need proper filling but are still a realistic DIY repair. Anything wider than 5mm, any crack you can fit a pound coin edge into, or any stepped crack that mirrors the brickwork joints behind, deserves a professional opinion before you cover it up.
A simple test: tap the render around the crack with the handle of a screwdriver. A solid, dull sound means the render is still bonded to the wall. A hollow, drummy sound means it has blown, in other words separated from the masonry behind, and filling the crack alone will not last. Blown render needs cutting out and patching back properly.
For a sound crack in the 1mm to 5mm range, pick a dry spell of at least two or three days, ideally with temperatures above 5°C. That can take patience in the Valleys, so late spring to early autumn is the sensible window.
Work through it methodically:
If more than about a quarter of a wall sounds hollow, or cracks keep reappearing after repairs, the render has usually reached the end of its life. At that point re-rendering the affected elevation is more economical than chasing cracks every year. Depending on access, wall size and the system chosen, re-rendering a typical elevation on a Valleys terrace tends to run from several hundred pounds for a small patch repair to a few thousand for a full wall in a modern silicone or monocouche system, so quotes vary widely and it always depends on what is found once work starts.
Modern through-coloured silicone renders cost more upfront than traditional sand and cement, but they flex with the building, resist the algae growth our damp climate encourages, and never need painting. For older solid wall properties, a breathable lime based render is often the right answer, because trapping moisture behind a hard cement coat is what caused the damage in the first place. A reputable local firm should explain which system suits your particular wall, not just quote for the cheapest option.
Paint will hide hairline crazing for a season or two, but it will not bridge a real crack, and water will keep getting in behind. Fill and seal the crack first, then paint, otherwise you are repainting the same wall every couple of years.
Flexible exterior fillers can usually be painted within 24 hours, but a sand and cement patch should cure for at least five to seven days before painting. Rushing this in damp Welsh weather is the most common reason repairs fail.
Usually not. Most render cracks are caused by weathering, age or the render itself, not the structure. The warning signs worth investigating are stepped cracks wider than 5mm, cracks that keep growing, or matching cracks visible inside the house, in which case get a builder or surveyor to take a look.