Roofing Defects: Specifying the repair of a slate roof
Scottish slate has a good reputation as a long lasting material. Recent research supports this, with many slates showing they have a service life of 150 years or more, in achieving this, there fixing and support requires repair and maintenance. It is sensible therefore to inspect slate roofs at regular intervals to spot any potential problems as soon as they appear. Regular repair is the best way to ensure any slate roof covering will remain watertight and continue to perform well. It is also advisable to repeat the inspection after a particularly severe storm or gale.
The above picture is a roof with welsh slates, slates from different areas of the world will have different performance characteristics. Spanish slate and Chinese slates have become relatively common place but can be easily distinguished from the Scotch and Welsh slate by their texture and Colour.
Scotch single nailed slated roofs are relatively easy to repair. Most repairs are completely invisible. However double nailed slate roofs are less easy to repair because invariably the slates have to be ripped out and unless they are at the top of the roof they can’t be re-nailed with two good nails. A slaters ripper is used by sliding it under the slate and hooking on to each nail, a hammer is used to hit the handle of the ripper and dislodge the nail. This method is effective but it can loosen slates in the surrounding area.
Some roofers who are obliged to undertake an invisible repair in these circumstances invariably resort to using high grab adhesive and glue replacement slates to their neighbours. The obvious issue with this is that if a further slate in the vicinity needs to be replaced it will be stuck to the previous slate repair and you will end up in a situation where you need to replace 4-5 slates as they are all stuck together.
A better answer is to use a visible fixing called a tingle although often the metal strip used for this purpose is not strong enough to do a good job. A lead tingle may end up coming loose over time leading to slates slipping, this is usually quite easy to spot. Plastic products are visible, unsightly and time consuming to install.
I would recommend the use of items such as the Hallhook™ which is a permanent, secret and fail safe device that can be used when replacing a double nailed broken slate.
The go-to fixing for most roofers will be galvanised clout nails due to their low cost. These will not last the test of time and will eventually suffer nail sickness (corrosion) when in contact with moisture. Copper clout nails are the premium option and should really be specified at the start of any major project and for any repair to give a long lasting solution.
When there is a roof leak, there is often an urge just to send the contractor out to fix the leak without specifying the materials to be used. To ensure the long term sustainability of the roof an appropriate repair should always be specified to ensure the contractor is not trying to implement short-cuts or use low cost materials.