The Brew Cabin

We had our drive blocked using clay pavers 8 months ago. I have noticed that on a number of the blocks the edges have broken off. This is mostly where the car wheels have drove over them. Is this something I should be concerned about?

Joe

Hi Joe,

this sounds ominous - are the edges definitely chipped/spalled?

Most clay pavers have chamfered edges which helps prevent spalling of this nature - are your bricks chamfered or square-edged?

The reason why this happens is that the bricks move slightly when trafficked and by pressing too tightly against their neighbours, the pressure is concentrated on the edges, which then 'spall'. This, I stress, should *not* happen on a properly laid clay brick pavement, which suggests to me that there's summat amiss with your driveway.

The most common reason for this sort of behaviour is that the contractor has either used an inadequte sub-base, or has omitted it completely. The sub-base is the load-bearing layer of the pavement, and it is absolutely essential as it ensures the individual bricks are capable of carrying the weight of cars, vans or foot traffic, without being forced into the ground beneath.

Do you recall a sub-base leyer being laid? It should be a layer of crushed stone at least 100mm thick, on which is laid the bedding sand and then the bricks themselves.

Take a close look at your drive in the daylight tomorrow - are the bricks chamfered or square-edged? Are the joints filled with sand right to the top? Is there any sign of 'ruts' forming where the car runs over the paving everyday? If you can provide me with the answers to these questions, I'll be able to give you more of an idea of what is happening.

Hi Tony, Thanks for replying

The blocks are chamfered on the very edge. The sub-base used was mill-waste, and it looked quite deep, probably at least 100mm. This was compacted with a wacker plate. As for ruts, yes there is one by the public footpath. It’s quite obvious when it’s filled with rain. I’m finding more freshly chipped edges each week. Most are 10-15mm across and about 3-5mm deep, although a couple are 10mm deep.

Joe.

Hi again Joe,

I'm not sure what Mill Waste is, as it can mean different things in different parts of the country. Up here in NW England, we call it quarry waste, and it's not always suitable as a sub-base material. With quarry waste, here's no spec governing the proportion of fines to lumps, so you can, theoretically, end up with a load that has no fines or is all fines.

I'm not quite clear on what you mean when you say "Most are 10-15mm across and about 3-5mm deep" - what are? The joints?

It sounds to me as though the sub-base is settling/moving and that is what is causing the bricks to spall. There's no easy solution to this problem, I'm afraid. In some cases, sealing the surface can prevent further movement, but in most cases, the only real fix is to lif the lot, get rid of the rubbish sub-base and start again with genuine DTp1 on a geo-membrane, if necessary. :(