sealing the joints of slab on ceiling

I have slabbed a vaulted ceiling with an insulated slab
Now I need to attach plywood to this in order to get a grip for a T & G ceiling finish

Can someone tell me the best way of sealing the joints of slabs and ceiling as a whole

I was thinking of stapling on some plastic and taping the joints in order to make it airtight

Any comments/ideas would be appreciated

breather paper/felt is the best to use
why use ply,a 2x1 would be ok easy and cheaper

I have this done and used siga tape
It was 45 euro for a roll which was just enough
thanks anyway

I'd be wary of sticking pieces of timber of any kind to an insulated slab.

They should be mechanically fixed to a durable substrate, like the rafters.

The insulation should go above this and the surface sealed.

FWIW

ONQ.