How to Repair Pitched Roofs
A pitched house roof may be covered with traditional slates, clay tiles or interlocking concrete tiles. All can fail and work loose; you can repair small areas of damage yourself, but large-scale repairs may mean wholesale replacement of the roof covering, which should be entrusted to a professional roof contractor. Never walk directly on a roof covering; use a proper ladder.
The most common cause of roof slates slipping is “nail sickness”, that is one or both of the nails holding a slate rusting through. The slate itself may be undamaged and still be on the roof somewhere. If only one nail has failed, use a slate ripper to cut through the other one. This tool is slid under the slate, hooked around the nail and given a sharp tug to break the nail.
With the slate removed, you will be able to see, between the two exposed slates, one of the timber battens (furring strips) to which the slates are attached. Cut a strip of zinc or lead, about 150 x 25mm, and nail one end to the exposed batten so that the strip runs down the roof.
Slide the slate back into its original position and secure it by bending the end of the zinc or lead strip over the bottom edge. Note that slates at the edges of the roof have mortar fillets beneath them to prevent the wind from blowing debris into the roof space.
Replacing a dislodged tile
Most concrete and many clay tiles are held in place by hooks, or nibs, on the top edge, which fit over the roof battens. If these are still intact, a dislodged tile can simply be replaced by gently lifting the surrounding tiles, supporting them on wooden wedges and slipping the tile back into position. If the nibs have broken off, the tile can be replaced in the same way as a slate. Edge tiles also have a fillet of mortar beneath them.
The curved tiles that run along the top of a tile or slate roof are mortared into place. With age and weathering, one or two may have become loose.
To replace ridge tiles, you need a roof ladder with hooks that fit over the ridge and wheels that allow you to run it up the roof from the top of a conventional ladder. This will provide a safe means of access.
Once you have reached the ridge, remove the loose tiles, then use a small trowel to scrape away crumbling mortar until you reach sound mortar. Dampen the tiles and trowel on a bed of fresh mortar.
Place each ridge tile gently into position, tapping it down with the handle of the trowel. Add mortar to the ends of each ridge tile to fill the joints with its neighbours and scrape off all excess mortar.
If you have a dual-pitch roof- different parts of the roof pointing in different directions – there will be a lead-lined valley between them to allow rainwater to escape and provide a junction between the tiles. Cracks can occur in the lead, allowing water to leak through.
A severely damaged roof valley will need to be replaced completely – a job for professionals. But simple cracks can be repaired with self-adhesive flashing tape. Once the area around the crack has been cleaned, the tape is applied – sometimes, a primer is needed first – and rolled out flat using something like a wallpaper seam roller.
For securing loose ridge tiles and packing under edge tiles and slates, use a weak mortar mix – no more than three parts sand plus plasticizer to allow some movement and prevent cracking.