Clay roofing tiles

[Lewism3]

Can anyone throw any light on the lamination of pre 1940s clay roofing tiles?

Yeah sounds strange, but I have to do a brief presentation on the subject. Finding research very tricky indeed. Any info or links would be appreciated.

Thanks

Lewis

 

[^woody^]

Do you want to define the question a bit more?

I understood that the tiles were just fired clay, and not laminated. Some powder (oxides?) were sprinkled on the surface to achieve colour varience, but thats it

 

[Roofer]

The delamination (spalling) of machine made clay Plain tiles is caused by water that is between the laps of the tiles (drawn there by capillary action) being absorbed into the surface of the tile then freezing, expanding and subsequently splitting the surface away from the body of the tile; this process is obviously repeated over the years eventually leading to the total failure of the tile.

This problem is more prevalent in tiles made during the 30's and 40's as this was when there was mass production of tiles by machine and they were made flat which meant the capillary action drawing water into the laps was greater. Prior to then tiles were generally handmade and the methods of firing the clay produced more uneven tiles.

Once the problem was recognised it became common practice to produce tiles slightly curved along their length (single cambered) or along the length and across the width (double cambered) which reduced the capillary action and prevented water being held between the tile laps.

 

[^woody^]

Oh, *de*-lamination.

I hope the OP does not get the two mixed up in his presentation

 

[Lewism3]

Sorry Woody, bit vague I know.

The sheet I have been given says lamination, but I think it really means delamination or spalling.

Roofer, spot on!!!!!!!

Thats just what I needed. I really required what changes were made to the process of production to make them more durable.

Thank you poeple, so very much appreciated.

Any further comments would be welcome.


Lewis

 

[Lewism3]

The research continues but I can't find much about pre 1940s clay tile manufacture.

Does anyone know how such tiles were made, i.e. the process undergone to form them, and also why the formation of a clay tile is laminated. Why doesn't it crumble when subject to spalling?

Lewis

 

[^woody^]

Can I suggest you do a bit of research on whe meaning of laminated? You seem to be confused in using this word in this context.

Lamination is the construction of an item by joining successive layers of material - plywood is an example. Delamination is a material coming apart in layers or strips - delamination is not confined to a laminated material, so can occur in materials whch are not laminated.

Clay tiles are not laminated. They are compressed lumps of clay which are then fired to make them hard.

Roofer explained how the tiles become 'delaminated' or they 'spall' - ie moisture in the clay (voids) expands and blows the surface of the tile off. It does this because of either natural fissures or voids in the clay, and/or because of the surface treatment of the tile - added before firing which may be slightly harder or have some other minerals added to give a surface finish or colour. So there is a natural inherent weakness in the tile.

Some clays may be more susceptible to this than others, so not all tiles will exhibit such delamination.

"BRE Good Repair Guide 20 - Repairing frost damage: roofing" (1998) gives some good identification and causation guidance, and also lists other relevent texts.

Have you contacted the manufacturers such as Redland, Marley and Sandtoft, for info about manufacture?

Also, delamination does not just happen to roof tiles, it can occur to all clay products. So you may want to research clay in general to discover how it reacts with water and particularly freezing

 

[Lewism3]

Thanks Woody, that's very helpful.

I have just downloaded a copy of Guide 20, looks interesting.

Lewis