In older properties, ridge tiles often become loose because of crumbling and breakdown in the old lime mortar. Cracked or crumbling mortar should be carefully removed with a hammer and chisel.
Brush away any loose dust. If the same ridge tiles are to be repositioned, make sure their undersides are cleared of old mortar and the tile is cleaned. Check the roof itself is clear of old mortar and mix a new bedding mixture.
Use a 1:3 cement: sand mixture. Make the mixture as stiff as possible, but a consistency that will fix the sections together, but not too loose as this could run and affect other areas of the roof and become unsightly.
Soak the tiles in water before fixing in position, as this will help the bonding. Dampen the top of the roof before making a mortar channel at the top for the tiles to sit on. This is necessary, especially in warmer weather, to stop the mortar from losing moisture too quickly, which would result in cracking. Set each tile on top of the mortar mix and push firmly into position.
Remove any mortar squeezed out with a trowel and try not to smear the tiles. The ridge tiles should be laid and set into position along the roof-line, using the same method already used on the roof.
Make sure there is a solid bedding of mortar at the end tile or where the tiles come against a wall in order to seal the open end of the ridge. If possible use pieces of broken tile bedded into the mortar mix and bed into position. The completed run does not require pointing.
If the ridge tiles seem firmly fixed but the cracked mortar between them needs replacing, rake out the gaps between the tiles.
Use an application gun to inject a bead of flexible non-setting mastic between the tiles. Choose a mastic colour to match the other tiles along the run. It is available in different colours to match the various shades of roof tiles available.