External rendering onto blockwork

[redlee]

After sifting through lots of old posts i'd like to check i'm going about rendering my extension the right way.
The extension is conc. blocks, do i need to rough up the surface or will a 1:1:1: slurry coat of cement, plastering sand and water be ok?
What thickness should the scratchcoat be and is 4:1 plastering sand, cement with a waterproofer right?
I intend to use a stopbead at the bottom does it just sit on top of the dpc and do i stick it to the scratch coat or before the scratchcoat is applied?
Is it ok if the scratchcoat is left for a week or more before the topcoat is applied as i'm fitting it in between my own work?
Top coat should be 5:1 plastering sand, cement with or without waterproofer?
should i be using any lime at all and if so when?
I'm pretty sure you can tell this is new to me although i do have a little experience of internal skimming any help is appreciated.
Cheers
Lee.

 

[Alastairreid]

Youre on the right track, you just need to dampen down the blocks before the scratchcoat.
Fit the bellcast bead along the line of the dpc before the scratchcoat.
Waterproofer in the scratchcoat and plasticiser to top coat.
Lime is optional it helps to plasticise the mortar and prevent cracking.
Its fine to leave the scratchcoat for a few days just dampen down before applying top coat.
your quantities are spot on.

Here's a helpful link //www.diynot.com/forums/viewtopic.php?t=142247

 

[redlee]

Thanks for the link i swear i havent seen that before even though i'd done a search on here and looked at loads of rendering posts.
Ok no need to scutch the blocks or slurry coat, is a bellcast the same as a stopbead? do i just stick it with a bit of render or does it need to be fixed with screws and plugs? I take it as a rendering newbie i'm better off using the plastic corner beads.

 

[Alastairreid]

Bellcast bead is for running along the line of the dpc and is designed to shed the water away from the building. http://www.catnic.com/pvcu_bell_cast_bead.aspx

You should be able to nail the bead on in the perp joints in the blockwork.

Yes use external corner beads it makes life a lot easier.