Loose scratch coat?

lemonbomber

Wondering what has gone wrong or is it wrong? I am applying real stone veneer on an interior wall as a hearth around a gas stove. I demo'd the sheetrock and put up cement board on the studs. I applied a scratch coat of S mortar over the cement board and allowed it to dry at least 48 hours.
I have been buttering the stones and then sticking them to the wall and all has been fine. It seems that at the 6 foot mark on the left side of the wall one of my stones is loose. Upon further inspection it is not just the stone/mortar not setup properly but the scratch coat it has adhered to seems to not have adhered to the cement board.On further inspection the scratch coat in this area did not stick to the cement board!
What could have cause this? Something on the cement board not allowing the mortar to stick? Was my S mortar mix too dry when I applied it?
Can I just peel this defective layer off and re-apply a new coat over the cement board?
Any ideas?

ddawg16

Did you apply the scratch coat to the cement board with the board dry? It's my understanding that you wet the cement board first....

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lemonbomber

Yes i did apply the mortar to dry cement board.
I was wondering now if that was a problem? A lot of info I have gathered online had recommended dampening the stones before buttering them to avoid them sucking all the moisture from the mortar too soon. Would dry cement board have the same effect. No where online did I see anyone advise to dampen the board.

jomama45

Always dampen the board first.

lemonbomber

Thanks for that advice.
Wish I had known sooner. Males me wonder about the other 6 feet of scratch i already stuck stones to.
Never heard from manufactuerer or anyone else to dampen the cement board first.
Thank you Lowes!

hankj

did you consider a layer of metal lath before the scratch coat? Not close to an expert but doing a similar project and most info I found recommended metal lath on smoother surface applications.

lemonbomber

WEEEELLLL, I considered the lathe and scratch coat but was told by some possibly misinformed people that sticking em to cement board with a scratch coat was a more professional method.
SHould have done more research online before starting. But live and learn- i hope I have learned well.
So i replaced the last 3 feet to the ceiling with lathe and scratch as for some reason the lower part of the scratch on cement board bonded tightly enough that to remove it was damaging CB.
As of today I have just touched the ceiling with most of my stones and should be done in two days depending on interruptions.
I will attempt to post a pic of the completed job as soon as then.

Thank you all for your advice and wisdom.