What Happens When a Mortar Verge Fails on a Roof in Aberdare?

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The mortar verge is the line of mortar that beds the tiles along a gable edge. On Aberdare houses it has often been there since the roof was laid, taking wind, rain and frost every year. When it fails, nothing dramatic happens at first, which is why people leave it. The problems build quietly.

How a mortar verge breaks down

Mortar is rigid, while a roof moves slightly with temperature and wind. Over time hairline cracks open along the bedding, and water gets into them. Once the mortar is damp, frost does the rest, expanding the cracks until pieces fall out.

Poor original bedding, shrinkage and the gradual loss of the bond between mortar and tile all play a part. The result is a verge that looks dark, patchy and loose. The result is a verge that sounds hollow under a gentle tap from below and looks dark and patchy, and it is already past the stage where a quick repoint will last.

What you see from the ground

Failure shows up in plain ways. Crumbs of mortar collect in the gutter, on the path or in the garden below. You may spot a gap between the verge tile and the wall, a tile that has slid out of line, or green staining down the gable face where water has been running.

None of that needs you to go near the roof. Walk round the house, look up, and note what you see. Make a note of what you see and when, because it helps us judge how quickly the edge is deteriorating, and a photograph from the ground is plenty.

• Mortar fragments in the gutter or on the ground.
• Gaps or dark lines along the gable edge.
• Verge tiles that sit crooked or have shifted.
• Damp staining on the gable wall below the edge.

What it lets in

A failed verge opens a path for wind-driven rain into the batten space under the last row of tiles. Moisture sits in the timber edge, and in Aberdare's wet climate that is a steady supply. Birds and insects also find the gaps and nest inside the roof edge.

If the water follows the rafter or the gable wall, you may see damp in a top-floor corner long before anyone connects it to the verge. That is why a failed verge on an Aberdare terrace end sometimes shows up first as a damp patch inside, well away from the actual fault.

When wind makes it urgent

Without sound bedding, the edge tiles are no longer held down. A hard gale coming up the Cynon Valley can lift them, slide them or take them off the roof entirely, which is a hazard for anyone below and an open door for rain.

If you notice a verge tile hanging or lifted, keep clear of that edge and call us. Do not try to push it back or refix it yourself. The same applies to any debris on the ground. Leave it where it is, keep children and pets away, and let us deal with the repair and the clear-up.

• Keep people away from the area below the damaged edge.
• Do not climb up to look at it.
• Photograph the damage from the ground for us.
• Call us to arrange a proper look.

How we put it right

We strip out the failed mortar, check the battens and last tiles, and fit a dry verge. That means mechanically fixed verge units and tile-ends with no wet mortar, secured to the tile maker's guidance. Compatibility depends on the tile profile, so we confirm it on site first.

It suits repairs, re-roofs and new roofs alike. It does not fix a roof failing elsewhere, and we will tell you if that is the case. Where the damage is limited to one edge, we can often do that edge alone, and we explain the sensible order of work so the rest can follow later.

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