Which door-blocking method?

[GuyStevens]

Hi all. I'm blocking a redundant doorway in an upstairs, floorboarded bedroom.

Several weeks ago I used lightweight thermalite blocks and a cement render prior to getting a plasterer in to finish off. Only now hairline cracks are appearing, presumably where the blocks meet each other.

What are the chances of these cracks appearing in the finish plaster? Should I start again with a timber-frame and plasterboard? If so, can you tape between plasterboard and a concrete wall to prevent cracking?

Thanks for any advice.

 

[Diyisfun]

I had similar problem, I opened the hairline crack & filled it, that was a year ago, it is still ok now.

 

[jbonding]

if you tape the joints before you skim it should be sound, most of the shrinking has happened with the backing.