rendering aircrete blocks

[DIYedboy]

My extension is being built with 215mm thick solid aircrete blocks which will need rendering. I have read loads about rendering failing on these blocks.
It seems that the render should not be stronger than the blocks............BUT even if the scratchcoat is 6;1 that's already much stronger than the blocks.

What is the foolproof way to ensure rendering is a success?

 

[roy c]

I haven't ever rendered outside thermalites but have dot and dabbed and also plastered inside blocks with browning (a light weight plaster). If anybody builds with these blocks then they must make sure that the "muck" they use is either weaker than the block or the same strength as the block, so they all dry out the same strength.So when putting the render coat on it should be the same strength as the the blocks and everything will dry equally. If not then it will eventually crack with all the different forces of the mortar in the joints and the render on the walls. I would look on the site of the blocks you are using and check out what they say about mortar and tolerances of the render that should be used. Have a word with you builder and get him to gaurantee that they wont crack out within ten or twenty or thirty years !!! This is just my opinion so having not had to render any outside aircrete blocks I cant say for definite. Have a look in your area and see if any of the houses done with these blocks have cracked or not, is it too late to use concrete blocks?