Calculating Sand, Cement and Lime quantities

[Rusty Wingnut]

Full disclosure: I’m not a renderer. But I want to understand how you work out quantities of sand, cement and hydrated lime needed for a specific project – primarily for materials budget planning, but also out of curiosity & education.

Assumptions:

• 6:1:1 mix ratio
• 235m² total wall coverage
• 10-12mm base/scratch coat (which will have a 10mm fibreglass mesh embedded)
• 8-10mm topcoat

As I understand it – and please correct me where I shall inevitably go wrong (Googling this info inevitably gives you many different answers!):

• Knowing the mix ratio and the 2 coat depths, I can work out a volume.
• But that will be for a “wet” mix, and I’ve read that you should add 54% to the volume for calculating the “dry” materials you will need to order.
• But you would order materials by weight – and weight vs volume obviously varies between different materials. I believe you can work this out by knowing the specific density of the material. Normally this density is stated as Kg/m³. Again, Googling specific densities to use for sand, cement and lime often gives me a huge variable range of answers.
• So, in theory, volume + 54% split between a 6:1:1 ratio for each of the materials required, then calculated as a weight by knowing their respective densities… should tell me how much sand, cement and lime would be needed by weight. (Please assume I have already factored in contingency in the volume calculation).

I’ve made a huge number of assumptions above, and I’m sure I may well be wrong about much of it! But in particular, I’m not at all sure I have understood the 54% wet to dry factor correctly. And densities may be better calculated by using just a single common density (Kg/m³) factor for all three materials?

I’d be really interested in knowing how others go about calculating these quantities. Thanks in advance for any guidance offered. Much appreciated.

 

[Monkey Boy]

Get one bulk bag of sand and crack on with scratch and see how far you get

 

[malc]

Mixing sand and cement lime for external render. You are 30 years out of date!
For sand and cement render use Tarmac One Coat Render. pre bagged just add water you have the perfect mix. It all finishes the same colour and the sand is sharp enough to give a perfect finish. 1 bag covers 1 metre square.
There are far more advanced external renders on the market. These are polymer based renders , umpteen systems to choose from.

 

[bobski]

Full disclosure: I’m not a renderer. But I want to understand how you work out quantities of sand, cement and hydrated lime needed for a specific project – primarily for materials budget planning, but also out of curiosity & education.

Assumptions:

• 6:1:1 mix ratio
• 235m² total wall coverage
• 10-12mm base/scratch coat (which will have a 10mm fibreglass mesh embedded)
• 8-10mm topcoat

As I understand it – and please correct me where I shall inevitably go wrong (Googling this info inevitably gives you many different answers!):

• Knowing the mix ratio and the 2 coat depths, I can work out a volume.
• But that will be for a “wet” mix, and I’ve read that you should add 54% to the volume for calculating the “dry” materials you will need to order.
• But you would order materials by weight – and weight vs volume obviously varies between different materials. I believe you can work this out by knowing the specific density of the material. Normally this density is stated as Kg/m³. Again, Googling specific densities to use for sand, cement and lime often gives me a huge variable range of answers.
• So, in theory, volume + 54% split between a 6:1:1 ratio for each of the materials required, then calculated as a weight by knowing their respective densities… should tell me how much sand, cement and lime would be needed by weight. (Please assume I have already factored in contingency in the volume calculation).

I’ve made a huge number of assumptions above, and I’m sure I may well be wrong about much of it! But in particular, I’m not at all sure I have understood the 54% wet to dry factor correctly. And densities may be better calculated by using just a single common density (Kg/m³) factor for all three materials?

I’d be really interested in knowing how others go about calculating these quantities. Thanks in advance for any guidance offered. Much appreciated.

Ratios and coverage rates were written on cement bags and wickes sand bags, similar mix designs to yours




I have my own way to work to my mix patterns - which are slightly different to those .......

 

[Stewie03]

Your trying to work out how your renderer has quoted you ex amount just ask him for a breakdown of the bill you tight git

 

[Cockney]

Full disclosure: I’m not a renderer. But I want to understand how you work out quantities of sand, cement and hydrated lime needed for a specific project – primarily for materials budget planning, but also out of curiosity & education.

Assumptions:

• 6:1:1 mix ratio
• 235m² total wall coverage
• 10-12mm base/scratch coat (which will have a 10mm fibreglass mesh embedded)
• 8-10mm topcoat

As I understand it – and please correct me where I shall inevitably go wrong (Googling this info inevitably gives you many different answers!):

• Knowing the mix ratio and the 2 coat depths, I can work out a volume.
• But that will be for a “wet” mix, and I’ve read that you should add 54% to the volume for calculating the “dry” materials you will need to order.
• But you would order materials by weight – and weight vs volume obviously varies between different materials. I believe you can work this out by knowing the specific density of the material. Normally this density is stated as Kg/m³. Again, Googling specific densities to use for sand, cement and lime often gives me a huge variable range of answers.
• So, in theory, volume + 54% split between a 6:1:1 ratio for each of the materials required, then calculated as a weight by knowing their respective densities… should tell me how much sand, cement and lime would be needed by weight. (Please assume I have already factored in contingency in the volume calculation).

I’ve made a huge number of assumptions above, and I’m sure I may well be wrong about much of it! But in particular, I’m not at all sure I have understood the 54% wet to dry factor correctly. And densities may be better calculated by using just a single common density (Kg/m³) factor for all three materials?

I’d be really interested in knowing how others go about calculating these quantities. Thanks in advance for any guidance offered. Much appreciated.

@John j

 

[Rusty Wingnut]

Your trying to work out how your renderer has quoted you ex amount just ask him for a breakdown of the bill you tight git

LOL No - nuffin like that at all! My msg was long enough as it was, so didn't want to bore peeps with every detail! The building belongs to a charity I'm a member of. We have a very limited budget, so have no choice but to DIY it . We have a handful of very keen and very capable DIYers, including one who used to be in the trade - but 20+ years ago. Before we start hacking off the old render (most of which is already just falling off, sadly), I want to know we can afford to finish what we've started! Hence my questions.

 

[Rusty Wingnut]

Mixing sand and cement lime for external render. You are 30 years out of date!
For sand and cement render use Tarmac One Coat Render. pre bagged just add water you have the perfect mix. It all finishes the same colour and the sand is sharp enough to give a perfect finish. 1 bag covers 1 metre square.
There are far more advanced external renders on the market. These are polymer based renders , umpteen systems to choose from.

Interesting you should say that - I was looking and wondering about Tarmac One Coat Render. But I was a little bit put off because I thought it sounded more suitable for (relatively) smaller areas and maybe repairs? The building has moderate to severe exposure to the elements... would this one coat be good enough over a large building and in those conditions? What do others think? Is traditional sand, cement and lime now history?

 

[malc]

Interesting you should say that - I was looking and wondering about Tarmac One Coat Render. But I was a little bit put off because I thought it sounded more suitable for (relatively) smaller areas and maybe repairs? The building has moderate to severe exposure to the elements... would this one coat be good enough over a large building and in those conditions? What do others think? Is traditional sand, cement and lime now history?

As you are thinking about putting mesh over the walls. it would be a lot better to bed the mesh into a coat of Rendaid with a decent scratch to key the finish coat.
As it is a very exposed property, use plastic angle beads. Not galvanised or stainless beads.

 

[malc]

LOL No - nuffin like that at all! My msg was long enough as it was, so didn't want to bore peeps with every detail! The building belongs to a charity I'm a member of. We have a very limited budget, so have no choice but to DIY it . We have a handful of very keen and very capable DIYers, including one who used to be in the trade - but 20+ years ago. Before we start hacking off the old render (most of which is already just falling off, sadly), I want to know we can afford to finish what we've started! Hence my questions.

Render is NOT a DIY project.

 

[Rusty Wingnut]

Render is NOT a DIY project.

As mentioned in a reply to @Stewie03 earlier, this is a charity organisation. The building is obviously very important to us, but the existing render is now badly cracked and chunks are falling off in places. Financially we really have no other choice. As I say, at least one member of the group is a former plasterer, but is not up to date with how volumes, etc (as per my original question) are calculated. The obvious answer is to make a start using smaller quantities, and take it from there. But I don't want us to make a start and find we can't afford to finish the job. Basically, understanding quantities of materials to order is one thing, but ultimately it is understanding the total budget for the project is key to getting approval to even start!

 

[Stewie03]

LOL No - nuffin like that at all! My msg was long enough as it was, so didn't want to bore peeps with every detail! The building belongs to a charity I'm a member of. We have a very limited budget, so have no choice but to DIY it . We have a handful of very keen and very capable DIYers, including one who used to be in the trade - but 20+ years ago. Before we start hacking off the old render (most of which is already just falling off, sadly), I want to know we can afford to finish what we've started! Hence my questions

A large job like that isn’t exactly diy but seems as you have no choice,I wouldn’t bother with traditional sand&cement like @malc said use a one coat render I use Weber, tarmac is great aswell just takes all the guess work out for ya with quantities,definitely use a rend aid with mesh imbedded you can scratch it or stipple it with a decent heavy duty roller,

 

[essexandy]

So the guys on a tight budget and yet people are suggesting using a bagged product, utter madness. There is absolutely nothing wrong with good old sand and cement, if done by the right people.