Fondant

[nemphlar]

Thanks for comments, as usual not a single point of failure in this hive, there were 8 completely empty frames around this cluster despite being fed late syrup last year, they didn't process enough late on and stopped taking it down, poor queen with probably old bees around OA treatment when the fondant was added and dwindled later. I understand that in a really cold winter 10 mm is probably too far, but a reasonable sized cluster in the mild winters we've had recently ought to manage. The sugar bag does seem to either maintain or draw cluster moisture more effectively than the fondant
C4u does the removal of the cover leave a rather large air space above the cluster

[Calluna4u]

Thanks for comments, as usual not a single point of failure in this hive, there were 8 completely empty frames around this cluster despite being fed late syrup last year, they didn't process enough late on and stopped taking it down, poor queen with probably old bees around OA treatment when the fondant was added and dwindled later. I understand that in a really cold winter 10 mm is probably too far, but a reasonable sized cluster in the mild winters we've had recently ought to manage. The sugar bag does seem to either maintain or draw cluster moisture more effectively than the fondant
C4u does the removal of the cover leave a rather large air space above the cluster

One or two points jump out at me from your reply.

Not taking syrup down in autumn, when others in the same group are is always a danger signal. In our unit a high proportion of these colonies will perish in the coming winter.
8 empty frames. Did you put this colony into winter with only three or four seams of bees? We do not expect a high winter success rate in these either, but add in OA treatment if by trickle and you have a serious problem. OA is savage on colonies that are small and can be the final blow that sees them off.

Surprised you find that the sugar bag is more effective at maintaining moisture than the fondant. It is in permeable paper bag while the fondant is in impermeable plastic, but having only done the sugar bag method one season in my earlier years I do not have enough relevant experience to pass much comment on that.

Large air space above the cluster is a point often made and is common sense. If it is a worry then you can always lay some insulation over the top of the fondant. Fleece, bubble wrap, sacking, the old hay sack idea, all can be done. For some reason it seems to make little difference. We usually just put the fondant on the top bars and have an inverted feeder over the top. (These are full size hive top feeders, Ashforth style, not contact type.) Cover board then just sits on top of that lot.

[nemphlar]

I normally add sugar bags when I open them to do the OA treatment,sublimation from the top, around December on this occasion they were on 4 frames near the side. I moved the clearer hole over the cluster and placed the fondant over them. Although the Q was that year she didn't really take off as I would expect and were most likely doomed.
I don't have any ash forth feeders so my eke is an empty super
The nucs had the fondant on the frames and still didn't seem to take much though the frames were empty, it did seem to dry and harden if not used quite quickly and if the bees couldn't access water then it is pointless. The sugar crystals appear to draw the moisture from the saturated air above the cluster