Brick up door opening in brick house with concrete blocks?

[konga]

Is it possible to brick up a doorway with leca blocks if the rest of the house is in brick (which is plastered with KC mortar, I believe).

Can I use KC mortar on the LECA blocks without the risk of cracks, or could I encounter other problems?

 

[Bricky]

It's going well, but start with cement slurry first, there are also special bags with (probably the same) stuff but I don't know what they're called and they probably cost a bit more.