Will the concrete weigh the insulation boards down???

[merlecollins]

Have been doing a bit of a 'project' lately and would be very grateful of some advice

I've been replacing an existing flagstone floor with a new concrete slab in a 200 year old stone house

I've dug 300mm out and so far filled it back with the following:

100mm Type 1 hardcore (whacked)
20mm Sand blinding
2 layers of 300 Micron DPM
80mm Quinn Therm insulation boards

Just a bit worried though

The boards aren't sitting completely firmly and some corners rock ever so slightly

Will the 100mm concrete layer flatten the boards into a firm base??

Also, because of the original construction of the stone walls the foundations was basically a large stone padstone course which I unearthed but have left in place - unfortunately the top of this foundation course is halfway through the new insulation boards How do I handle this? Do I simply butt the boards to the foundation course and fill the difference with concrete?

Hope that makes sense

 

[themiddleagedun]

The sand is hard (impossible?) to get truly level. The BC guys are quite keen on that round my area. Having a good walk on it to check for movement.
Perhaps you could take off any "high spots" to stop it rocking?
Though I'm sure the ins. would flex slightly and sit flat.
As for the footing stones. I would do as you suggested.

 

[^woody^]

Stamp on the insulation board to crack it or indent it from beneath, or cut it diagonally across the corners and then it will sit better as the two parts flex

Or take some of the board out at the back to effectively make it a thinner board where it sits on top of the old stone