In article ,
Harry Bloomfield writes:
I told breeze block is quite suitable for outdoor use, can anyone

Real breeze blocks haven't existed since 1930's, so you'll
need to be more specific about exactly which blocks you mean.

confirm this is the case and/or advise on an alternative light weight
building block?

Thermal blocks do expand and contract slightly when they get
wet and dry out, enough to cause plaster to crack or lose key
and to crack the blocks themselves if layed wet and they dry
after the mortar has set. Also, they act rather like a sponge.

There are probably better products available if you don't need
the thermal properties, but I've never needed to investigate.
Alternatively, a waterproof finish, such as a render with a
waterproofing additive might be OK.

--
Andrew Gabriel