To lime or not to lime, that is....

[milou22]

Hello all,

Just a small pointer if anyone out there could oblige please... About to render externally onto dense, concrete blocks and have conflicting advice about the mix to use. I'm anticipating using a 5:1:1 (washed sharp:cement:hydrated lime [+waterproofer]) for my scratch coat and a 6:1:1 for my top coat. Not having rendered before and hunting around this and other sites, I don't see too many people suggesting the use of lime anymore. I wonder what you fellas (and ladies?) might advise?
Many thanks.

 

[noseall]

use lime, it will fatten up the mix.

read any threads by this fellah,//www.diynot.com/search/forum-author.php?search=legs-akimbo

 

[milou22]

Many thanks noseall, just wanted confirmation really and a little reassurance. Will take a shoofty at the fella you mentioned. Thanks again.

 

[andyrich7496]

Hello all,

Just a small pointer if anyone out there could oblige please... About to render externally onto dense, concrete blocks and have conflicting advice about the mix to use. I'm anticipating using a 5:1:1 (washed sharp:cement:hydrated lime [+waterproofer]) for my scratch coat and a 6:1:1 for my top coat. Not having rendered before and hunting around this and other sites, I don't see too many people suggesting the use of lime anymore. I wonder what you fellas (and ladies?) might advise?
Many thanks.

i would go for a 4;1;1 and it is fine sharp sand
you use not sharp sand

 

[andyrich7496]

Hello all,

Just a small pointer if anyone out there could oblige please... About to render externally onto dense, concrete blocks and have conflicting advice about the mix to use. I'm anticipating using a 5:1:1 (washed sharp:cement:hydrated lime [+waterproofer]) for my scratch coat and a 6:1:1 for my top coat. Not having rendered before and hunting around this and other sites, I don't see too many people suggesting the use of lime anymore. I wonder what you fellas (and ladies?) might advise?
Many thanks.

i would go for a 4;1;1 and it is fine sharp sand
you use not sharp sand

p s i would go for the same mix for both coats

 

[milou22]

Thanks Andyrich. Yes, it is fine, sharp I'm using...didn't mention that did I! As for the stronger mix, I'm tempted but have had conflicting advice so will perhaps find a happy medium.
Thanks again.

 

[andyrich7496]

Thanks Andyrich. Yes, it is fine, sharp I'm using...didn't mention that did I! As for the stronger mix, I'm tempted but have had conflicting advice so will perhaps find a happy medium.
Thanks again.

it is not that strouge a mix and you dont want
your mix to sandy or you may have touble floating it up and you have lime init as well

 

[Limespred]

I don't want to tread on anyone's toe's over this but I was always taught that a sharp sand with lots of angular stuff in it is much stronger than a sand without.If you get some sand,put it in a jar of water,shake it up and leave to stand for 24 hours.When you next look at the jar,if it's a good sand it should have 4 to 5 different layers of sand,bigger bits at the bottom.

 

[Micilin]

Do not use lime with waterproofer. We've had this debate in the past and I'm still waiting for anyone to give me a w/p manufacturer that will allow you to add lime to their product.

I can give you manufacturers that say you must not add lime to their w/p . Which ones? Any one I've ever used ! Their phone number is on the container, just ring tech and they will tell you.

If you need w/p , put it in the scratch coat without lime. A decent product will give you the workability.

Then use lime in the top coat , as it will give you a better texture,workability , rub up nicer and make the render less prone to cracking.

Always work from stronger coat to weaker coat ( stronger on first) .

On to dense blocks

4:1 (sand and cement ) with W/P for scratch coat

5:1:! (sand cement lime) for finish coat