self-levelling compund

I've just put some Febfloor down on an old concrete floor: at the same time I embedded in it some underfloor heating cable. I'm slightly worried the layer hasn't set properly. It is quite thick, 5-6mm, and in some places if you push hard on the surface , the crust breaks and it seems awfully powdery underneath. I laid it about 30 hours ago.
Is this how it should be, or should it be more solid like cement ? Could this be caused by adding too much water to it when it was mixed? Or is it that it has not properly cured yet because of its thickness ?
I'd like to be sure as I plan to put ceramic tiles on top of it and I am worried that the layer might not be cohesive enough to take the tiles (I plan to use a continual layer of tile cement 3-4mm thick on top) and may work loose. I'm also slightly worried that the underfloor heating cable might have an additonal effect on the compound, if there is something wrong with it.
Anny ideas, advice, experince ?
Trab
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Trab Nospmis wrote:

Did you PVA the old floor first to stop water being sucked out of teh cement?
If you didn't, I'd advise spraying it with water...

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wrote:
<snip>

Yes I gave the concrete 3 coats of PVA 1:5,1:5 and a final 1:2.
However I might just take your advice and give the floor a small spary.
ta
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