Slab over Slab

[WoodyG]

I have a home on a concrete slab. I have an existing screened porch area on a slab which I am going to increase in size and need to raise up to meet the existing slab in my home another 1 1/2 or 2". . Can I pour over the existing slab? Not even the concrete experts in my area seem to know the answer to this one. The finished area will have a floating laminate floor over it. I am worried about the long term cracking and flaking issues. If you can't pour over the existing, is there any other solution other than removing the entire existing slab which appears to be 6-10" thick?
We are in the mid-Atlantic east coast area.

 

[Tryan]

You should talk to your local building authority and discuss what you are proposing.Where I come from {OZ} that room would be classed as a "non-habitable" room and as such is subject to different regulations than your house which is classed as "habitable" ie.You must maintain a step down from the level of your house slab.This may not be a problem where you are, so back to your question.Of course you can no matter where you live in the world! The process is called "topping" and is a very common procedure.I will need more info on your size increase,is it on a perimeter footing,are you dismantling the existing structure and the condition of the existing slab?

 

[boo1]

The two important issues to consider are: cracking at the discontinuity (notch) of where your new slab will overlap the old slabs edge, and vapor barrier (porch slabs typically dont have any installed under them).

Both can be minimized. The slab will crack but, with your floating flooring system it should not be a problem. Insure the concrete is clean and use a bonding agent. Utilize a Mono slab design (12"x20" footer). You should drill the sides of the old slab and some 1/2 rebar dowels (epoxied in place)to tie the slabs together. Use the same approach to tie the new footing the the existing. Consider your flost line depth for the footer depth. You can add the vapor barrier to the top slab (after cure) with a sheet of 6 mil poly or a painted yop sealer (or both).