groundwork to support mesh reinforcement for raft ?

[coxsox]

Hi

Just dug out over the weekend in prep for the raft foundation of my extension. I have a question regarding details under the raft. The SE has drawn 100mm of Type 1 and the 75mm of lean mix blinding on top of type 1, all underneath the raft. Can anyone tell me why the blinding is necessary, SE mentioned something about stopping mesh support chairs sinking into type 1, but if I buy the mesh supports that are on small concrete blocks I presume I don't need to do this blinding layer.

Would ask the SE, but as its the weekend.....

thanks

 

[Norcon]

Just use concrete and forget about stones. Unless you need the height?
Hard to beat a hard/level surface for laying down re-bar.

 

[coxsox]

I've already got 5 tonne of type 1 sitting on the drive, the thing is the ground is also very hard clay which the digger struggled to get through, can't see anything sinking into that thing, so thinking just put the type 1 down, whack it, then mesh on top leaving out lean mix blinding. Otherwise I'll have to dig down another 100mm possibly, which I don't want to do.

 

[Norcon]

All it needed was dug to the right level and then a skim of concrete.
No need for all that faffing around with stones and whacker plates. These guys in their fancy offices have some funny ideas.
Even re barred direct to the hard ground would do as long as its level.
If it rains though it might get sticky.

 

[coxsox]

thanks but doesn't resolve my problem

 

[Norcon]

Lattice type stools won't sink into the whackered type 1. Even bricks should be ok. Depends on the spec of the steelwork. Smashed up paving slabs make good stools.
We use a 22 ton daewoo to do the whackering.

 

[coxsox]

thats whats I thought, although there are specific products to elevate the mesh by 50mm from base, there must be cheaper and equally as suitable solutions for this. Gonna go ahead a whack down the type 1 anyway and see where that leaves my levels before deciding next move.....thanks all.

 

[Norcon]

You could use concrete bar.
http://www.sdg.ie/construction-technology/accessories/concrete-bar/

There's also steel wire lattice or plastic flatfoot spacer. sdg supply them all and they supply us but we tend to avoid them when we can because of cost. Hence the use of smashed up paving slabs or bricks.