What mortar mix is used for ridge tiles?

Ridge tiles run along the crown of a pitched roof, and each one is laid on a cushion of mortar so that it sits level and the hollow beneath it is filled. The everyday recipe is building sand and cement. A usual proportion is roughly one part cement to three or four parts sand, gauged to a workable, slightly stiff consistency rather than a slop that slumps off the tile.

Plasticiser is a common addition. It makes the mix easier to place and helps it hold together while it sets. Some roofers also add a colour oxide so the pointed edge blends with the tiles, since bare grey cement against a dark clay ridge looks patchy from the pavement. Sharp, clean sand grips better than soft, dirty sand, and a mix with too much cement shrinks and splits as it cures.

Our page on why ridge mortar cracks follows what goes wrong when the mix, the weather or the movement of the roof get the better of a bed.

Lime mortar is softer and more forgiving than a cement mix, and it lets damp escape from the joint instead of trapping it. On a stone-slate cottage, a Victorian terrace with an original clay ridge, or any building where the existing bedding is lime, a lime mix is the natural match. A hard cement bed laid on a soft, ageing roof can crack the older material around it, because the cement does not give where the old fabric does.

With a protected property, whether listed or in a conservation area, learn what the first bedding was before anything is cleared, and take any consent worry to Swindon Borough Council's planning team. Our guide to heritage ridges goes through the materials and the questions to ask.

Matching the colour and texture of an old bed takes a little trial and error, and it is worth doing on a small patch first.

For a long time the bed was the entire fixing. Marley's guidance records that, before the 2014 revision of BS 5534, a bed with no other fixing was commonly accepted. The revision changed that: the tensile strength of mortar cannot be counted on to keep ridge and hip tiles in place, so they are fixed mechanically too.

In practice each tile is tied down with a clip, a bracket or a screw into a batten, a ridge board or a timber that will take it, and the mortar does the filling and sealing around that. Mortar has not been banned, and plenty of ridges are still bedded in it. What has changed is that a ridge laid in the very best mix, with nothing else holding it, falls short of current practice.

That is why, when a tile slides, the useful question is rarely which recipe to use. It is whether anything is actually fixing the tile to the roof.

Good bedding is mostly habit. Mortar should be gauged in batches small enough to use before it starts to stiffen, because a mix that has begun to go off and is then loosened with extra water loses strength. Tiles that are filthy or bone dry draw moisture out of the bed too fast, so a quick brush and a light dampening of porous clay help the bed take hold.

Depth matters too. A bed that is thin at one end of a tile and thick at the other sets unevenly and cracks along the change. Mortar should fill the hollow under the tile fully, with no voids where water can sit and freeze, and the pointed face should be struck off cleanly so rain runs away from the joint rather than into it.

Work in rain or on a frosty morning is best left alone, because a bed caught by frost in its first hours never gains its full strength.

A dry-fix ridge uses clips, a batten and a ventilated roll or strip instead of a wet bed, and the products are tested to BS 8612:2018. Nothing in the system can shrink or craze the way a bed does, and the crew can keep working through damp spells that would stop a bedding job. The trade-off is looks: some owners prefer the neat pointed finish of a traditional ridge, and some older roofs suit it better.

The right route depends on the tiles, the age of the building and what lies under the existing ridge. See cracked ridge tiles for the choices on a single damaged piece, and ridge rebedding for a whole run.

If a gable end is part of the job, dry verge on an old roof and blown dry verge caps cover the sloping edge, where the same question about mortar arises.

We do not pick a recipe from a catalogue. At the survey we check what the existing bedding is made of, how it has aged, whether the tiles and the timbers beneath will accept a fixing, and how exposed the ridge is to the wind. After the survey you get pictures from your own ridge together with a written quote that covers only what the fault needs, which is sometimes a repoint and sometimes a full rebed with fixings.

Our 10-year workmanship guarantee is in writing, and after the work the site is left clear. To book a survey ring 01793 626096, or write to us on WhatsApp or through the form. The wider choices between mortar, lime and dry-fix sit on our ridge and verge page, so you can see the options side by side first.