What mortar is used for ridge tiles?

A ridge bed is a plain mortar. Sand gives it body, a binder makes it set, and water makes it workable. The binder is most often cement, sometimes lime, sometimes a blend of the two. The mortar fills the space between the underside of each capping tile and the tiles of both slopes, and it seals that gap so wind and rain cannot get underneath.

We have not printed a ratio here, because a figure copied from a website is a poor guide to a particular roof. The right mix depends on the kind of tile, the age of the roof, the weather on the day and the sand to hand, and a good roofer adjusts it by eye and feel. Hard sun and damp weather change how a bed sets, which is one more reason a fixed recipe is no substitute for judgement on site. What you can usefully ask for on a quote is the type of mortar, not the proportions, along with the reason it suits your tiles.

On a modern roof with concrete or clay tiles, a cement-based mortar is the usual choice. It sets reasonably quickly, bonds well to the tile and is familiar to every roofer. On an older roof, especially one with soft, handmade or reclaimed tiles, a lime-based mortar is often the better fit, because it is more forgiving of movement and is closer to what the roof was built with.

BS 5534 concedes that some of its advice can sit awkwardly with old roofs re-tiled using salvaged or traditional material, so the repair is matched to the roof in front of us. Whichever binder is chosen, the sand should be clean and suited to the job, because dirty sand weakens the bed and shows as staining. If your house is listed or protected, our guide to lime mortar on ridge tiles explains the thinking, and consent questions go to the council.

The bedding is visible along the lower edge of the capping, so its colour counts. Plain grey cement against warm clay tiles looks heavy from the street, while a mortar tinted to sit between the tile shades looks quiet and tidy. Colour comes from the sand as much as the binder, which is why mortar from a different bag can look noticeably different on the roof once it dries. The finish matters as much: a neat, flush bed running in a straight line shows care, where a smeared one invites water to sit.

It is worth matching the capping tiles themselves too. A mortar can be mixed to suit, but new ridge pieces in the wrong profile or colour will always stand out against the old. We cover that in our answer on matching ridge tiles. Edges that are straight and neat from the pavement are part of the finish we aim for on every roof, and they cost nothing extra to ask for.

Marley advises that mechanical fixings belong with every bedded tile and fitting, because mortar's own grip is not enough for ridge and hip pieces. The mortar seals and beds; the screws, clips or brackets hold. A stronger mortar does not take over that second job, and a very good mix with no fixing is not finished to the current code.

The reverse is true as well: you cannot rescue a poorly bedded ridge with a fixing alone, since the bed supports the capping and keeps the weather out. Both need to be right. Marley also notes that working to BS 5534 is not a legal requirement, though it is the standard we use on ridges and verges. For the detail, see BS 5534 for ridge tiles.

You do not need to specify the mix, but a handful of questions are fair. Which type of mortar will go on, and why does it suit this roof? Will each tile carry a mechanical fixing in addition to its bed? Will the colour be matched to the tiles? Is the old bed being cleared right out, or only patched over?

A roofer who explains things clearly and backs the plan with pictures of your own roof is giving you a proper quote. The survey leads to a written quote with one overall figure. Ask too whether the old mortar will be taken away and the area cleared, since broken pieces should not be left in your gutters. If you are weighing a bedded ridge against a dry-fixed one, the ridge tile repairs page sets out both routes, and what each one looks like when finished on a roof like yours.