What specification of mesh should I use?
This question should be answered by your site engineer as there are a number of parameters which govern the need for particular meshes and which are unique to the site and outside the control of the mesh manufacturer.
Why use bar chairs?
Reinforcing fabric is most effective in the top half of a slab when used for crack control. In this position it acts in tension to hold the concrete together when cracks develop. Left at the bottom of the slab or lifted in the concrete at the time of pouring, the mesh is ineffective. Choose bar chairs that lift the surface of the mesh to approximately 50mm below the finished concrete surface.
How many bar chairs do I need?
Bar chairs should be placed at 1.0 metre centres regardless of sheet specification or size. They are designed to carry the weight of a man standing on them rather than the weight of the mesh so lighter sheets should not have wider spaces.
Do I need to tie the sheets together?
The sheets should be fastened together to prevent any accidental movement during pouring. The number of ties and the material used to tie the sheets should be adequate to perform this task. The ties do not contribute to the strength of the reinforcement or the formation of the lap strength. Ties should be folded down so as not to project into the concrete cover over the mesh.
How much rust is acceptable on mesh?
There have been a number of engineering studies carried out on rusty reinforcement with the consensus of opinion being that the usual levels of rust encountered do not reduce the effective cross sectional area of the steel by a larger amount than allowed in manufacturing tolerances and that the surface of the steel may well be better bonded with rust present. The corrosion is found to be halted once encased in concrete.
A paper reviewing 13 studies by various researchers is available from Hurricane Wire Products by request.
What is the New Zealand equivalent to this Australian specification?
The following is a quick reference for equivalents to standard Australian Square Meshes. More comprehensive information on other Australian and International codes is available from Hurricane Wire Products on request.