Hearth slab pour - problem - not adhering to cement backer board base?

[Cheesehead]

Hello,

I just poured my hearth slab yesterday. I used a pretty flat surfaced cement board as a bottom base (instead of plywood) for the concrete.

I took an end form off and it looks like the concrete did not adhere to the board. Did I jump the shark in my concrete mix/pour? The day turned into a pretty hot one (after a cold spring, who'd have guessed the temp would soar to near 90?). I did pool water on top of it after it set to keep it cool/moist.

The hearth slab and base are pretty heavily rebarred.

[Cheesehead]

And upon further inspection, note to self - the cement board I'm using has a rough side and a smooth side. The smooth side is as smooth as a baby's you know what.

If I want mortar or cement to stick to it, use the rough side not the smooth side.

Meh. Maybe I can recycle some of it for the enclosure.

[brickie in oz]

I dont think itll be a problem as the cement sheet or ply is only there as form work, once set the slab should be self supporting.