This reply to only to be read by proper plasterers not DIY'ers or chancers. I've done plenty of externals and hundreds of internals over Celcon and Thermalite blocks and have never had any problems. I really don't think there is any need to slurry or Rendaid these blocks and you definitely don't want to be soaking the walls before hand. Give the walls a light spray before the scratch coat but once you've got the scratch done you must keep the render moist by spraying for at least three days, five being the ideal. Also when rendering over lightweight blocks getting the strength of your mix and thicknesses right is more important than ever. DO NOT MAKE YOUR MIX TO STRONG.
Yeah, I always 'scud' them and never had a problem...............new word to me though - 'scud':RpS_thumbup:
We just 'splatter-dash':RpS_biggrin:
Is this what parex have said?...sure I seen a data sheet and it was max 6mm render
EXTERNAL : good soak down with water day b4 if possible, then lightly hose about 20 mins before scratch. BS is 5-1 for therms on the scractch coat (with feb/waterproofer), Then 6-1-1 (lime, no admixtures), no need for pva it remulifies in contact with water/render. Also if u soak them down and the PVA hangs around... if u try to apply the scratchcoat, it will slide and the bond will be broken between the render and the therms.
NO NEED FOR REND AID / SBR, why would you try to make a key on a block wall that already has a key (high suction block), but its a good point Irish_Spread made about the SBR blocking the pores...
Because you are killing the suction to make them ok to render, there fore it requires a mechanical key!