The short answer
Mortar falls from a gable verge because it has weathered. The verge is the tiled edge beside a gable wall, and the mortar there is exposed to rain and wind from two sides. Over time the cement washes out, frost opens the joints and the tiles lose their grip. A repair can re-point the mortar or replace it with a dry verge system.
Pieces of mortar on the path are the roof telling you the verge bedding has run its course. What to do next depends on what lies behind it.
Why a verge weathers faster than the rest of the roof
Beside a gable wall, the last row of tiles is bedded in mortar along the wall top. That mortar faces the weather from above and from the side. It sits where wind catches the roof hardest, and where rain running off the wall lands on the bedding.
Why does it crumble rather than crack?
The cement binder is slowly washed out by water, leaving loose sand behind. Frost then works into the open grains and breaks them away in lumps. The result is mortar that falls out in pieces, often on the windward gable first, instead of a single clean crack. You might find grit on the path, a pale streak down the wall, or a hollow sound when a gloved finger taps the bed.
The mortar also meets the sun on one side and damp on the other, so it flexes more than a joint along the top does. Our page on why ridge mortar cracks describes the same process along the crest of the roof. At a gable the effect arrives faster because two faces are exposed to the weather.
The undercloak and what sits behind the mortar
Beneath the verge tiles there is usually an undercloak, a strip of material laid along the wall edge to support the tiles and send rain on to the slope. It can be fibre cement, slate or a purpose-made strip. It stops rain from getting behind the verge and into the wall top.
Does the undercloak need to be checked?
Yes. When the mortar falls away you can often see it. If the undercloak is cracked, rotten or missing, the verge will fail again whatever new mortar goes on top. A sagging line along the gable edge is a clue that something behind has given way, and one tile sitting lower than the rest deserves a closer look.
The timber behind the undercloak may also be damp. We look at these parts from a tower or ladder and photograph them, which gives you the real condition of your gable to judge for yourself. If damp has reached the wall head, a loft check is added to the survey. A roofer who points only the visible mortar misses these causes, and the verge fails again within a season or two.
Re-pointing or a dry verge system?
Re-pointing means raking out the loose mortar and filling the joints with fresh mix, a job that takes patience and a steady hand. It suits a verge that is otherwise sound, where the tiles are firm and the undercloak is good. It is a repair, and it restores the look of the original edge without changing the roof. Good re-pointing matches the old mix in colour, because a bright new joint beside weathered mortar stands out from the road.
When is dry verge the better choice?
When the bedding has gone along the full gable, has been patched before, or the tiles are loose in their bed. A dry verge system caps the edge with units fixed by screws and clips, so nothing relies on mortar holding on. Our page on the dry verge system shows how it goes together.
Dry verge does not suit every tile or house, as our page on fitting dry verge to any roof explains. On a listed or conservation-area home, a change of finish may need consent, so check with Somerset Council's planning team before ordering anything.
What to do while it is falling out
Look from the ground at the gable edge, note which tiles are exposed, and photograph the gap. Do not pick at loose mortar from a ladder. Pieces that come away easily may have tiles loose behind them, and a tile that drops can injure someone below. Sweep up the debris so it does not block a gully.
Is rain getting in through the gap?
It can. An open verge lets wind-driven rain run behind the tiles, and the timber at the wall head can get wet. If you see damp marks inside the gable wall, or on a bedroom ceiling nearby, mention it when you call.
If a piece of mortar or a tile has already dropped, keep the path below free of people. We can make the edge secure first and carry out the repair after the survey. The pictures show your own gable, and the written price covers whichever finish suits it. Our overview of dry ridge and verge work sets out the options. A clear photo from the ground is a good place to start.
More on verge mortar
Can I patch the verge with new mortar myself?
A fresh patch on weathered bedding rarely bonds well, and working at a gable edge from a ladder is risky. New mortar also hides loose tiles and a failed undercloak. A survey shows what lies behind it before anyone fills the gap, and it saves a second repair.
Does falling verge mortar mean the whole gable needs redoing?
Not necessarily. If only a short length has weathered and the rest is firm, a local repair is reasonable, and the survey photos show which case you have. Where the whole edge has gone, one proper job on the gable costs less than returning to it every winter.
The full picture: Dry ridge and verge repairs in Taunton ยท More short answers