Pattress Plates

A pattress plate is a name for an anchor plate for a wall tie.

The term “pattress” is believed to derive from the French patrice or patresse, referring to a backing or support plate.

Structurally speaking, they are the method by which the very concentrated force in a tensioned wall tie is spread out onto a wide area of material to avoid local failures. The tie may pass through a building or structure and have an anchor on both ends, or may be driven and fixed into embedded material, to help tie back a retaining wall.

Sometimes, such as a railway viaduct that could not be excavated for installation, pattress plates may be present on both sides, but not actually connected. Their presence normally shows that a repair was carried out, but doesn't give much indication of the current condition of the structure. NDT (Non-Destructive Testing) measurement of the tie tension is difficult, and will need to consider seasonal temperature effects.

An example of a forged wrought iron pattress plate from Germany. S shapes are relatively common on agricultural buildings in the UK.

An example of a cast iron pattress plate from Wells-next-the-sea, Norfolk. The lack of thread and nut on this end of the wall tie suggests that tightening was applied at the other end, or inside the building.

An example of a 1985 ductile steel patress plate. The off center bulge is to accomadate and spread forces from a wall tie that is an an angle to the wall. In this case, it is tying through a corner.

In historic building practice pattress plates were used to:

• Provide a solid fixing where masonry was weak, uneven or friable.
• Distribute point loads over a larger area.
• Create a true, flat plane for ironmongery or fittings.

They were commonly made from timber, slate or metal and were often built into the wall or floor during construction, rather than being surface mounted.

In classical and medieval masonry embedded timber pattresses were used to:

• Anchor iron straps, tie bars and railings.
• Receive door furniture and shutter hinges.
• Support grilles, hooks and wall-mounted fittings.

In these contexts, the pattress plate acted as a sacrificial or replaceable interface between hard masonry and metal fixings, reducing damage to the surrounding stone or brickwork.

When gas lighting, bell systems and early electrical fittings were introduced in the nineteenth century, builders adopted the pattress plate concept. A timber pattress was fixed or built into the wall, plaster was run up to it or over it and the fitting was screwed into the pattress rather than the masonry.

This is still visible in Victorian buildings where switches or bell pulls are mounted to flush timber pattress plates, sometimes hidden beneath decorative plates.

This idea has developed into the modern concept of the patress box, positioned behind power sockets, light switches and other electrical fittings, and containing wiring, switches and other circuitry. This may sometimes be secured to a timber or plywood pattress.

See Pattress for more information.

[edit] Related articles on Designing Buildings

• Aqueduct.
• Anchor beam
• Bolt.
• Bridge.
• Earth anchor
• Expansion anchor
• Fixing.
• Ground anchor
• Mechanical anchor
• Pattress.
• Percussion driven earth anchor
• Viaduct.
• Wall tie failure.
• Wall tie.