Monday, February 2, 2015

What is wrong with this photo?

I was on ebay this weekend and stumbled across this product, not one our ours I hasten to add.
Do you know what's wrong with it?


On the face of it, it looks like a standard grid system, designed to keep the ground stabilised and prevent the gravel from moving around, but it has one fatal flaw.

On a hot day (yes they do happen, even if it doesn't feel like it at the moment), all plastic grids will expand slightly. If the grid is entirely made up of straight lines, each one wil push against its neighbour, which will then push against the next one and so on, mean that by the time this expansion has made its way to the edges of the matrix, this displacement can easily be 100mm or more.

This will cause buckling and distortion right across the entire installation, resulting in just the kind of mess that the grids were put there to prevent.

This is why is it essential that any ground protection grids you buy have curves within them, as those same curves will absorb the thermal expansion and maintain their geometric stability, ie. remain the same size.

Obviously, our Hebden 402 grids aren't the only ones with curves, but they are good place to start if you are thinking about laying a permeable surface that is strong enough to carry type of road vehicle.

"Curved is the line of beauty" said Henri Matisse. Was he talking about our Hebden 402 grids?