Laying a concrete floor - shrinkeage?

[tonyjeffs]

I'm shortly going to lay a new concrete floor in our kitchen. I generally know how to do it... I plan to tile directly onto it without a screed.

What I'm concerned about is this:

1. I want it to finish exactly level with the timber floor in the adjacent hallway. I'm worried that after the concrete is in place and the suppliers have left, it will shrink as I tamp it and level it. Or perhaps it will shrink slightly as it sets. Is this likely to be a problem?

1. The idea of a polysterine insulating layer seems a little uncomfortable. I imagine that no matter how well I compact the sand and hardcore below ,and the concrete above, I have this springy layer that could compress under load and allow the concrete floor to crack. It seems a structural weak link. I gather it is not part of the building regs, and I could leave it out. Comments?

Thanks

Tony

[Frank]

Not an expert on this but AFAIK

1. Shrinkage of the level should not be a problem. It would be so minor as to be not significant. Shrinkage from side to side would be more of an issue. When I laid concrete slabs and floors, I was advised by an engineer to ensure that there was a barrier (i.e. plastic sheet) between the surrounding walls and the new slab. If the slab binds with the wall, the shrinkage can cause damage. Probably only a problem on very large slabs.

1. I would recommend insulation under the floor. The slab should be thick enough so that compression under load is not a problem. (I think a 4inch slab was the minimum recommended when I did this a few years ago.

[The Natural Philosopher]

Yes. Which is why SCREED is generally used. Its much drier, and there is less shrinkage as it ecvaporates.

Ever stood on blue foam? it won''t, and if you are bothered lay some rebar mat over it before screeding.

Dont be silly, Its not weak. It just has to be done properly. Get some pro screeders in a and some readymixed screed on tap.And at least 50mm of insulation..

[tonyjeffs]

OK will do that incl screed. I've not heard of blue foam. I imagined white polysterine. Will look into that. Tony