More Digging

Now the walls are up to damp course level I can start to think about the floor.  I needed to dig all the existing soil from within the walls down to the bottom of the second bock down - a depth of about 450mm.  I think this would be about 3 tonnes of spoil, though after a few days of rain it felt like 10.

I could back-fill the trenches both inside and outside the walls with some of the soil, but there was still a huge amount to shift and I am running out of places to put it.  I am pleased that it is a relatively fast-draining, sandy soil that digs easily - I'd hate to do the same in the clay-soil we have at school!

I left a small gap in the wall to put planks through as a bridge so I could use the wheelbarrow to move the soil, but eventually I had to brick this up too.  Once down to the required depth I could start to bring back some of the bagged brick and concrete rubble I had stored from the demolition of the conservatory to use for the bottom layer of the floor.

There are several strata to lay:

• First a layer of 150 mm of compacted crushed concrete etc. to give a good, firm base. This is sometimes called Type 1 MOT because it is the standard of material specified by the Ministry of Transport for making the sub base for a new road.  I am going to use the bags of rubble I have made up from the demolition and clearing of the conservatory.  I have plenty of this and when it is compacted using a plate compactor it should be absolutely fine.
• On top of this comes a 'Blinding' layer of 25 mm of sand.  this covers any sharp edges and points that may puncture the damp proof membrane which sits on top of the sand.
• This is covered by either a 100 mm concrete slab or a 75 mm insulation board. It seems there are different thoughts about the order that these go in.  Some websites suggest the insulation board goes on top of the damp proof membrane on the sand, others that the concrete slab goes there with the insulation on top, and there are others that put the damp proof membrane on top.
• Whatever order these go in they are topped with a 50 - 75 mm screed to give a perfectly smooth and level floor surface.

The removal of all the soil from inside the walls took a while but was useful for back-filling around the outside of the walls on top of the foundations.  There was still plenty to get rid of, but I like digging.

I left the part nearest the drive until last because it made a very useful little access bridge but eventually even that needed to be demolished and the concrete drain-surround removed.

The hard-core went in well though the hire of a compactor was not without its problems.  The first one I hired worked for a couple of minutes but then stopped and would not be coaxed back to life even with fresh petrol and a new spark-plug.  So money returned I hired an identical one from HSS - identical in all ways except one - it worked!  Unfortunately this had left me considerably out of pocket and having lost a couple of hours of work time.

The sand I had dug out for the foundation trench would be fine for the blinding layer if it was sieved for stones - so I set about sieving a ton or so of it to lay a 25 mm layer.  The compactor worked well and the base was ready for the building inspectors to view before I lay the damp proof membrane and the concrete slab.