What is expanded metal?
Expanded metal is sheet metal that has been slit and then stretched, so that the cuts open into a regular mesh, usually of diamond-shaped holes. It is neither welded nor woven: the whole mesh is one piece. The inventor, John French Golding, received his first British patent for it in 1884, and the Expanded Metal Company still manufactures in Hartlepool.
No material is removed during expansion, which is the difference from perforated sheet, where the holes are punched out. The sheet grows in area as it is stretched, and the cold working makes the metal harder and stiffer. Because the strands are never cut free and rejoined, the mesh keeps its strength, and it is stronger than the same weight of wire netting such as chicken wire. It is made in steel, stainless steel, aluminium, copper and brass, and steel for outdoor use is galvanised or powder coated.
Recognising it
- A mesh of diamonds whose strands are set at an angle, giving a slightly corrugated surface. This is standard or raised expanded metal.
- Flattened expanded metal has been rolled level after expanding, giving a smooth surface without sharp raised edges.
- Sizes are given by the long way of the diamond (LWD), the short way (SWD), strand width and thickness. LWD and SWD are measured from bond to bond.
In practice
- Specify all the dimensions. Give LWD, SWD, strand width, thickness, material and whether you want standard or flattened mesh.
- Choose the type for the job. Heavy mesh for treads, walkways and grilles; fine mesh as metal lath for plaster; decorative mesh for ceilings, balustrades, screens and facades.
- Use galvanised or stainless outdoors. The many cut edges are where rust starts on bare steel.
- Have spans and fixings checked. For walkways, treads and guarding, the supplier or a structural engineer should confirm mesh and thickness for the loads.
- Protect your hands. The cut edges are sharp; wear cut-resistant gloves.
For concrete construction joints and stiff plaster backing there is a separate form with rolled-in ribs: see ribbed expanded metal.
Common mistake: ordering standard mesh where a flat surface is needed. The angled strands make it uneven and sharp-edged; flattened expanded metal is the right choice.
Related terms
- Ribbed expanded metal
- Plaster base
- Wire brick lath
- Pressed metal ceiling
- Welded wire mesh
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