Ridge Repointing and Rebedding

On many tiled and slated roofs, the ridge and hip tiles are bedded in sand-cement mortar along the apex and hips, with mortar also pointing the joints between them. Over time this mortar cracks, shrinks away from the tiles and erodes. Loose ridge tiles can then rock, let rain in, or blow off in strong winds. Repointing (renewing the visible mortar) and rebedding (lifting the tiles and relaying them on fresh mortar) are common maintenance tasks, particularly in the UK, Ireland, Australia and New Zealand.

Why mortar fails

• Thermal movement and roof movement crack rigid mortar.
• Weak or poorly mixed mortar and laying in unsuitable weather; one UK manufacturer notes mortar needs dry conditions and temperatures roughly between 5 °C and 25 °C (41-77 °F).
• Frost and wind-driven rain erode joints.
• Mortar shrinks and loses adhesion to smooth tile surfaces.

Manufacturers have warned that mortar can begin to fail within the first few years after completion.

Repointing versus rebedding

Repointing alone only helps when the bedding beneath is still sound and the tiles are firmly attached. When tiles are loose or the bedding has crumbled, the tiles are removed, the old mortar cleaned off, and the tiles relaid on new bedding.

UK standards and dry-fix systems

In the UK, the 2014 revision of BS 5534 stated that mortar's tensile strength cannot be relied upon alone to secure ridge and hip tiles, so bedded tiles also need mechanical fixings. A 2018 amendment linked dry-fix systems to BS 8612, the test standard for dry-fixed ridge, hip and verge products. Dry-fix systems use clips, screws and ventilated rolls instead of mortar and reduce routine maintenance. For heritage buildings where a traditional mortar appearance must be kept, mortar bedding may still be used, outside the scope of BS 5534, with suitably specified mixes.

Practical notes

Ridge work is at height on an exposed part of the roof and normally requires scaffolding or edge protection. Matching original tiles is important on older buildings.