Render mix

[sako]

Hi.I wonder if anyone can help?I have a garden wall built from 6" solid blocks which i am going to render my question is what is the correct mix for both undercoat and top coat??I have read somewhere that one is supposed to be stronger than the other.
Also i am going to do it myself using 12 thick grounds for the undercoat and i am assuming anything from 3mm to 6mm is sufficient thickness for the top coat?Any help would be most appreciated.
sean.

[lutonlagerlout]

4 plastering sand to 1 cement for both coats but the secret is plenty of waterproofer
LLL

[Artisan]

We use 4 to 1 for the scratch coat, and 5 to 1 for the top, that way, the top coat doesn't pull off the scratch, and if it needs to be repaired, is easier to remove and reskim. Not sure what "12 thick grounds" are? ???

[sako]

Hi.Thanks for replies.I meant to type 12mm thick grounds.
Because i haven't plastered before if i fit vertical grounds i will be able to plaster each bay and it will give me exact thickness.
Could i use rendamix?or is waterproofer different?

[Artisan]

What height is it? Are you using beads? If so, you can use them to set your depths. Remember to use either stainless or plastic beads, not galvanised. We use febmix.

[lutonlagerlout]

a ground is like a timber profile, a lot of old houses had them at skirting height and then at picture rail height
proper way to plaster if you ask me,the walls are actually plumb this way
LLL

[sako]

Hi.The wall is a retaining one and on what will be lawn side the height is only 2 blocks and the other side is approx 6 blocks high.
Is the addition of lime essential??As i have read it on another site that you only need lime in top coat but always waterproofer.
When using waterproofer does it act as a plasticiser?If so would feb be ok to use as a waterproofer?? I take it you only use one or the other or are they both the same??Thanks chaps.
sean.
PS i will be using stainless angle bead the one in builders centre is 16mm i think so i will pack it out with mortar so i have 12mm undercoat and 6 ish top coat.

[lutonlagerlout]

feb is not waterproofer,feb is plasticiser
i have made this mistake my self,you need to use waterproofer as per manufacturers instructions which means lots of it about a litre per mix i think
who mentioned lime?
also its worth priming the wall first .i use PVA with good results but i am sure ronafix does the job better
or you could really go the whole shebang and nail EML to the wall
the beads are up to you,if you are using grounds then you don't necessarily need beads but they do give a nice finish
when fixing your grounds those little packers that window fitters use are invaluable for getting things on a nice flat place

all the best
LLL

[Artisan]

Rendering is one of those building jobs that has an almost infinte variety of ways in which people do it, however I bow down to LLL's experience in this matter! Lime was traditionally used to improve the workability of the render, that is replaced now by Febmix. PVA is a water based solvent that isn't ideal for outdoor rendering, instead use SBR.

[lutonlagerlout]

artisan what you are saying is correct too.
i have done lime courses and have many books on building with lime etc
the problem is that the lime you buy in BM is hydrated lime,which is quick lime with a small amount of water added to it.this lime is a great plasticiser but bears no relation to real lime and will not set hard

for render and stuff you can use hydraulic lime which goes off like cement (romans used this) or what they used to do where they mixed quicklime with sand and water and left it to cure for weeks,the problem with the last one is that it takes 6 weeks to go hard and needs a lot of back up attention,going back and misting every day
good luck
LLL

[sako]

Hi Thanks for the replies.The beads are for the corners of the pillars that are on the 2 returns of the wall.Lime was mentioned on another site ,in fact this is what a builder stated.
scratch coat 4-1 dont have to use lime in scratch coat(i wont be using any anyway) use waterproofer in summer but in dead of winter none needed in scratchcoat but always in top coat which should be 5-1.
So would i be correct in saying that the addition of waterproofer enables the top coat to be worked for longer??
sean.

[Mikey_C]

you can get 3in1 admixtures which are a plasticiser, waterproofer and retardant. as detailed on here i am guessing by the questions you are asking you haven't done much rendering before, as a DIY'er who will tackle most things (and has) rendering/plastering I find very difficult to get even a reasonable finish, IMHO you might want to call in a pro.

[lutonlagerlout]

water proofer stops water ingress funny enough :;):
the plasticiser reduces the amount of water needed and helps workability
dont buy 1 of those rendering sponges they are crap,the good old bath time sponge works a lot better
FTR i havent done loads of rendering but i have had loads done and watched how they do it
LLL

[sako]

Rendering sponge what,s one of them?? I think i will get a 3in one additive and give it a go.Cheers
sean.