Introduction
There are two types of clay tile.
Plain tile
Plain tile is a type of fired roof tile, normally made from clay. Flat tiles normally lap two courses. 18th Century Tiles were made of local clay by hand, and therefore vary in colour and size. Clay plain tiles are flat, and are laid like slates.
Pantile
Pantiles is a type of fired roof tile, normally made from clay. It is S-shaped in profile and is single lap, meaning that the end of the tile laps only the course immediately below. A pantile-covered roof is considerably lighter than a flat-tiled equivalent and can be laid to a lower pitch. {image of Pantiles}
What to look for
The most common problem is loose or broken tiles so regular inspection is important. Clay tiles will deteriorate with age and frost damage as they absorb water.
Clay tiles are sometimes bedded in mortar as are clay ridge tiles. Use Lime Mortar at abutments.
How to fix
Brushing moss off tiles (which holds water onto the roof) will reduce the effects of deterioration but eventually clay tiles will need replacement.
If it is possible the existing tile should be re-fixed. If you are replacing a broken tile, ensure that it matches exactly in size and profile and is made of clay not plastic.
Use Lime mortar because is more porous and slightly flexible, compared with cement mortar, thus accommodating movement of the timber structure below.
Pantiles are ‘S’ shape in section and interlock to form a series of ridges and troughs. The side-laps of pantiles are at the high point, channelling the water into the troughs away from the joints. If the roof space is not properly ventilated this can cause the roof to ‘sweat’.
Avoiding creating problems
From the early 20th Century, roofing material was mostly Clay, or Concrete/asbestos mix, and are inappropriate for older period houses.
Modern concrete tiles are not appropriate where traditional clay tiles & pantiles have originally been used, and may affect the life of the surrounding clay tiles.
Mortar repairs must always be carried out in lime mortar, not cement, for the following reasons:
- Cement mortar is hard and impervious while clay tiles are soft and porous. When a clay tile is set beside a hard mortar the rainwater evaporates through the more porous surface, ie. the clay tile. This exaggerated wetting and drying cycle is concentrated in the tile which will accelerate its deterioration.
- It is tricky to loosen tiles bedded in hard cement mortar which leads to unnecessary breakages and loss of original tiles during future repairs.
Historical background
Clay roof tiles were first introduced to United Kingdom from the Netherlands, however by the 18th Century England had its common practice to lay felt under the slates when re-slating roofs.
Roofing pantiles are not to be confused with a type used for paving, after which the Georgian colonnade in Tunbridge Wells is named. Whilst called pantiles, the paving tiles which were installed there in 1699 were one-inch-thick square tiles made from heavy Wealden Clay, so-named as shaped in a wooden pan before firing.