A rendered house on the Devon coast takes more weather than almost anything inland. Salt-laden air, driving rain off the sea, and wind that puts the water on the wall horizontally. Sand and cement render cracks under it and lets water in behind. Silicone and lime survive it, for different reasons.
Three things, and they compound.
Salt gets into the render and into the wall behind it. Salts are hygroscopic, which means they pull moisture out of the air, so a salt-contaminated wall stays damp even when it has not rained. That is why coastal walls get that permanently patchy look.
Driving rain is the second. Rain falling straight down runs off a wall. Rain thrown at a wall at forty miles an hour goes into it. Exmouth, Dawlish, Teignmouth and the whole of the south coast get a serious amount of it.
And the wind moves salt inland further than people expect. You do not have to be on the seafront to get this.
It is hard, it is brittle, and it shrinks as it cures. So it cracks. Not always visibly, but it cracks.
Water finds the crack. Once it is behind the render, cement is exactly the wrong material to be sitting behind, because it will not let the water evaporate back out.
So the wall stays wet. Salts get carried through it. Frost gets into it in winter and blows the render off in patches. And every one of those failures started as a hairline crack somebody could not see.
Sand and cement is cheap. On the Devon coast it is a false economy.
Silicone and silicone-acrylic renders, of which K-Rend is the best known, are through-coloured and highly water-repellent while remaining vapour-permeable.
That combination is the whole answer. Rain beads and runs off rather than soaking in. But water vapour from inside the wall can still get out, so the wall is not sealed the way a cement render seals it.
It is also through-coloured, which means the colour goes all the way through the material rather than sitting on top as paint. That matters more on the coast than anywhere, because painted render on a salt-blasted seafront wall needs redoing constantly and through-coloured render does not need painting at all.
It is more expensive up front. On a coastal property it is the cheapest thing you will ever do.
If the wall is cob, stone or solid brick, a modern silicone render may still be too tight for it. Lime is the traditional answer and it is still the right one.
Lime is soft, breathable and mildly self-healing, in that fine cracks close up over time. It has been standing up to Devon coastal weather for centuries, which is a reasonable body of evidence.
The catch is that lime needs the right weather to go on and to cure, and it needs painting or limewashing periodically. It is more maintenance. On a period coastal building it is still the correct choice.
Whatever goes on the wall, look at what is above it.
Blocked gutters, a failed downpipe, a missing bit of flashing, an overhang that is too shallow. Water coming off a roof onto a wall will beat any render you can buy. Fix the hat before you worry about the coat.
Half the failed render jobs we see on the coast were not really render failures at all.
Send a photo of the wall on WhatsApp and we'll tell you straight what it is and what it needs. No charge, no hard sell.