Advice on rendering lightweight blocks


New Member
Evening all,
I have built an extension which is in lightweight blocks [Ytongs] which are fairly smooth. I am intending to two coat render 4/1 scratch [with or without waterproofer/SBR?] and 5/1 top coat. Now I have done a fair amount of plastering and some rendering but I want to get this right!

The more I enquire the more different approaches plasterers use! My main concern is the fact they are smooth [ish] there is no scratching on them so I know I will have to key them. But should I prime the wall or just wet it? And what additives should I use in which coat? I suppose its about 30m2 to do and the plastering sand is already here!


New Member
Hi badger, if the blocks are thermalites (thats what they sound like) you will need a scud coat or id use micro gobetis a parex product to kill the suction. You van always check the suction by chucking some water on them and seeing how quick they dry or do a test panel scratch coat and see how it goes off


Private Member
I would use a render grit or sbr if there smooth , the mix ratio should be at a max 5/1 and 6/1 top coat