Good day firends,
Is it okay to use those grey, lightweight Thermalite Aircrete blocks for bricking up a window in a cavity wall? The outside of the wall will be rendered with sand & portland cement afterwards. As it's just a window I want to brick up, it will not be load bearing. I'm mainly concerned about the moisture absorbtion tenedencies of these blocks. (They soak up damp like a sponge, don't they? I'm not sure if that's an issue or not. Does rendering stick to them okay?)

Many thanks,

JD