Why ridge tiles take the brunt of the weather
Ridge tiles sit along the very apex of a roof, capping the joint where two slopes meet. Because of that position they catch the worst of everything: wind-driven rain, sleet, frost, and the full force of gales that funnels up the pitch. On a traditional slate roof, those tiles are usually bedded and pointed in mortar, and that mortar is the part most likely to fail first.
Look closely at a ridge that has been up for thirty or forty years. The pointing has often gone grey and chalky, with hairline cracks running along the joint. In places it may have crumbled back to leave the tile edges exposed, and you can sometimes see daylight or feel movement if you press gently on a tile. Moss and lichen in the joints make it worse, holding moisture against the mortar through the winter. Frost gets into those cracks, expands, and prises the mortar apart a little more each time.
The consequence is rarely dramatic at first. A loose ridge tile lets water track down into the roof space, often near a chimney stack, where it shows up as a damp patch on a ceiling or a stain on a bedroom wall. In a strong gust, though, a tile that has lost its grip can lift and go altogether. Once one goes, the two either side lose their support and the risk spreads quickly along the ridge.
Choosing the right time of year
Late summer and early autumn are the ideal window. You want a dry, mild day with temperatures comfortably above 5°C and no frost forecast for at least forty-eight hours, because mortar needs that time to set before it freezes. A gentle breeze helps it cure evenly; a heatwave does not. On a hot day the mortar dries too fast, shrinks, and cracks before it has bonded properly, so work in the morning or on an overcast day and keep the joints damped.
Avoid working on a wet roof for obvious reasons, and never on a frosty one. If rain is due within a few hours, wait. Spring is the second-best window, but autumn is better for a simple reason: you want the ridge sound before the first severe weather arrives, not after it has already done its damage.
Tools, materials and the right mortar mix
For a traditional roof, a mortar of three parts sharp or washed sand to one part cement, with lime added for flexibility, works well. Sharp sand gives grip and strength; building sand is too soft for this job. On older properties, a mix closer to one part cement, one part lime and six parts sand is more forgiving and more breathable, and it moves with the roof rather than fighting it. A mortar dye or a paler sand can be used to match the existing colour rather than leaving a bright grey stripe along the roof.
You will need:
- A pointing trowel, a small tuck pointer for tight joints, and a hawk
- A half-round jointing iron for striking the finished profile
- A club hammer and bolster chisel, or a raking tool, to remove old mortar
- A stiff brush, a plant sprayer or hosepipe for damping and cleaning down
- Gloves, safety glasses and a dust mask
Modern dry ridge systems, which use stainless steel screws and clips instead of mortar, are worth considering on very exposed sites. They are not traditional, but they hold up well in coastal and upland areas.
Repointing the ridge, step by step
Rake out the old mortar to a depth of around 15–20mm, deep enough to give the new mortar something to key into but not so deep that you loosen the bedding beneath. Work along the ridge in short sections rather than trying to do the whole length at once.
Brush out the dust, then damp the joint with a fine spray. Damping stops the dry tiles and old mortar sucking the water out of the new mix before it can cure. Press the mortar into the joint with the tuck pointer, building it up in layers and packing it firmly so there are no voids. Once the joint is full, strike it with the jointing iron to leave a smooth, slightly concave profile that sheds water rather than trapping it. Run the tool along the tile edges to seal the mortar against them, then clean off any smears before they set.
Leave the finished work alone for a few days. If the weather turns hot, mist the joints lightly each morning to slow the drying.
Working at height and when to call in help
Ridge work means working at height, and that is the real risk, not the mortar. A properly secured roof ladder hooked over the ridge, or a scaffold tower for anything beyond a straightforward single-storey roof, is essential. Never walk on the slates themselves, and never straddle a ridge without fall protection. If the pitch is steep, the slates are fragile or the height makes you uneasy, bring in a roofer. It is a small job for someone with the right access equipment and a serious one for anyone without it.
Looking after the rest of a traditional property
A sound ridge protects more than the loft. Water tracking down past a failed joint can soak chimney flashings, stain plaster and eventually find its way into the stone or flagstone flooring of a hallway below, where damp shows as a dull, dark patch that never quite dries. Traditional stone floors set on lime mortar need to breathe, so avoid sealing them with impermeable products that trap moisture underneath.
Treat the ridge as part of a seasonal routine: clear gutters and downpipes each autumn, check flashing around the stack, and look along the ridge line with binoculars from the ground after any major storm. Ten minutes of inspection twice a year is usually enough to catch a failing joint while it is still a small repair rather than a leak.
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