rendering blocks

When applied properly, rendering will provide a water resistant barrier on your block work. You can render onto thermalite but it would be a good idea to seal the block work first (as it is a highly porous substrate) using an sbr and either scat(Harling coat) the wall, this can be a bit messy but it will provide a very good key once dry and it is also cheaper than using EML. Or you can seal the wall and EML it ready for a scratch coat and top coat render. I personally prefer to use a Harling coat it is a more traditional method and the key is solid on the wall once dry. Whereas EML can be time consuming and I feel like it will blow off the wall sooner. It is still a good product but I feel it has its own particular uses. Hope this helps Daved of Prides Plastering.