The Brew Cabin

I am laying a 100mm sub-base around a manhole. The drain and inspection chamber is Victorian. I do not want to disturb the brick work forming the inspection chamber. Do I use DTp 1 and a wacker plate? Is there another kind of sub-base I can use which doesn't require vibrating?

I am going to put 100mm of fibre concrete on to the sub-base and use a light reinforcing mesh (A142). The condrete will then be tiled with Victorian mosiac tiles to form a path leading to a domestic front door. I do not want the concrete to break, as the tiling is going to cost an arm and a leg!

Many thanks in advance for your help, Phil

Is there some reason why your think the brickwork of this Victorian MH is unstable, Phil? If it's survived the last 100 years, it's probably quite sound!

All sub-bases need compacting, alough, with a concrete sub-base (CBM) you can get away with using less force than is required for an unbound material such as DTp1. In your shoes, I'd take a peek inside the MH just to make sure it wasn't crumbling or collapsing, and assuming it's ok, then use the DTp1 sub-base and wacker plate as normal, but try to avoid letting the plate 'rattle' the brickwork of the chamber by coming into direct contact with it.

If there's any doubt in your mind, then a punnelled sub-base would probably be ok for the 300-450mm or so nearest the MH itself. This is simply sub-base material that it literally hammered down with a punnel or the head of a sledge hammer/maul until it is firm and compact.

If this path is only to take foot traffic, why do you think A142 mesh is required as well as the poly-fibres? You won't do any harm by including the mesh (as long as you remember the minimum 50mm cover rule) but it seems excessive to me.