Fretting on a terracotta roof tile has various causes and salt is one common culprit. However, it is quite a difficult task to pin point the exact cause of the fretting. Some particular brand and production run of roof tiles seem to suffer a lot more than others. Some very old terracotta roof tiles do not fret – yet younger tiles do. Some terracotta roofs near the sea suffer bad fretting, while others fair quite well.
… And the problem is that most of the fretting problems occur under the lap of the roof tiles – so it is not immediately obvious where the problem tiles are. Each tile has to be inspected by lifting up the neighbouring tiles.
For roofs with no sarking, it is usually easier to inspect for fretting from the roof cavity – because the terracotta colour powder of the fault will fall onto the surface of the ceiling and the roof battens. This layer of dust is easy to spot. With sarked roofs, it is a bit more difficult.
A short term solution is to replace the tiles that are badly fretting. But fretting is a bit like cancer. It can be quite wide spread and you should consider a new roof if there is substantial fretting of your terracotta roof tiles.
… Another cause of fretting terracotta roof tiles is salt or chlorinated water on the roof. How does it get up there?
Swimming pool heating elements.
These rubber tubes can spring a leak from time to time and if the home owner is unaware of the leak, bad fretting will happen.
Just like on the video below: