How Long Does Roughcasting Last, and Why Does It Fail?

The honest range

A roughcast coat put on a sound background with the right mix lasts decades. Plenty of the houses round here are still carrying their original finish from between the wars.

What ends one early is almost never the finish itself. It is water getting behind it, movement in the wall underneath, or a mix that was too strong for what it was stuck to.

The four things that kill a coat

Water from above. A blocked gutter running down the same line of wall for years is the single most common cause we see. The staining is the warning; the debonding comes later.

A mix that is harder than the wall. Too strong a sand and cement mix on an older, softer background cannot flex when the wall moves, so it cracks and lets water in.

Paint. Painting a roughcast wall seals it, and a wall that cannot breathe holds the water that gets behind it. When the paint eventually flakes it takes dash with it.

A rushed backing coat. Joints of the blocks showing through the finish in the first couple of winters is that, and it cannot be patched away.

How to tell where yours is

Tap it. Sound render rings; render that has let go sounds hollow. Walk the wall with a knuckle or the handle of a screwdriver, low down and round openings first.

Look for black streaking running out of a crack, which means water has found a path behind the coat and is bringing dirt out with it. And look at the gable before the front: it takes the driving rain and usually has no overhang to shelter it, so it goes first.

Repair, gable, or whole house

One failed patch on an otherwise sound wall is a repair. The catch is colour: new dash against twenty years of weathering will not match, which matters on a front elevation and often does not on a gable or a back wall.

Several hollow areas across an elevation means patching is chasing it round the house, and the sensible answer is to take that elevation back and do it properly.