Wall of lightweight expanded clay blocks

[evaerixon]

We have built a wall of leka blocks that is now plastered. The wall is meant to support a deck. The plasterer said we need to place a sheet on top of the wall, a so-called Murbeslag, to protect the leka from absorbing water & cracking. The carpenter says it's enough to place roofing felt on top under the decking. Who is right?

 

[b8q]

Both should work, provided it is syllpapp (or a strip of takpapp), i.e., asphalt paper that does not let water through.