Foundations above lowered slab

[pdaj0463]

I have lowered my slab by around 500mm and this has meant that the foundations are now slightly above the top of the slab by about 50mm around the doorways. The plan is to put 50mm insulation and then 50mm of screed on top of the slab.

Is it preferable to cut or grind the foundation concrete down to the level of the slab and insulate over it or to just insulate to the edge of the foundation and let the screed equalise the levels (probably this will still require some removal of the foundation although not as much)?

What is the best way to reduce the foundation level?

Thanks.

 

[Himaginn]

I suspect your second option would lead to a cold spot on the floor and thus condensation.
Perhaps your first option is a better solution.
Obviously a DPM needs to be incorporated along with insulation.

The only reasonable way to reduce the inner skin is with a 250 mm grinder to make vertical and horizontal cuts, then finish with the chisel.
A series of vertical slots then chiseled out will be partially successful.

 

[pdaj0463]

Thanks for your response. I tried with a 115mm angle grinder and it can only cut a couple of cm depth so I felt that it was going to take forever. Then I contacted a concrete cutting company and they quoted £1200+VAT to do the work. Perhaps the best thing to do is to rent a bigger angle grinder.

 

[r896neo]

If your going to rent something then a stihl saw would be better. As the door is on i assume the room is now relatively wind tight, using a grinder will be horrible with the dust and very slow going plus you'll only get about 60mm per cut.

A stihl saw has water suppression which will cut the down down a lot, it will cut a full 100mm in one go and most importantly it has a clutch and when cutting in awkward areas like this it is a lot safer.

I wouldnt even dream of trying to cut numerous horizontal slots at floor level like that with a 9'' grinder unless you like broken wrists.

 

[mfarrow]

Have you considered stitch drilling instead?

You may get through a few SDS bits but it's a hell of a lot cleaner than a grinder.