Workshop extension. Concrete hardcore

[Shiny Steve]

Hello people. I'm debating extending my workshop (big garden shed thing, 3 course brick then timber frame). I built the original thing a few years ago 150mm slab with deeper troughs 250mm around the outside 6mx 5m over rough ruble hardcore.

My question is how best to extend and join the slab 3mx6m so total floor of 8x6. Then do I need to put down a hard core base. Soil is fence London clay(Kent)

 

[gaz1]

are you extending width or extending the rear of the original build

if your extending the width all you would need is 150mm slab with deeper troughs 250mm around the outside

if extending to the rear you make another floating slab to same 150mm slab with deeper troughs 250mm around the outside

 

[Shiny Steve]

Extending the front out, so workshop is currently 6m wide 5 deep. I want it to be 6 wide 8 deep. Hopefully this make sense

 

[Shiny Steve]

Would you join the two slabs any way and would you bother with the hard core underneath.

I was going to key in the brickwork? Good or bad?

 

[frank horton]

drill the original slab and epoxy rebar into the holes leaving at least 250 sticking out...also but not comp nec, bend a squiggle in the sticky out piece....
this will lock the 2 slabs together.....
if u dont and the slabs move a bit the bricks will crack / break...
they are not strong enough to hold things tight.....
a little hard core will help, I tend to use type 1 and wack it for a bace...
guess u'll use some mesh....?

 

[dobbslc]

Same as Frank ^
I extended two sides of my old garage base the same way, drilled the edge and bonded a few lengths of rebar in, laid 6" of crush then poured the concrete. The joint never moved over the 10 years I was there. It was also on London clay.

 

[Agroshield]

...If you don't and the slabs move a bit the bricks will crack / break...

Even if you do that, it may still move and crack. It might be better to make the joint one which will accommodate movement should it occur.

Drill and grout smooth (plain mild steel) bars into existing. Paint protruding part of dowel with debonding compound or put on plastic debonding sleeve. 10mm closed cell foam with tear off strip along joint. Once new slab is poured, tear off strip and fill joint with polysulfide sealant. Standard movement joint with mastic to any associated brickwork.