When it comes to laying concrete blocks, there are several materials required. This will include sand and cement which are the ingredients required to make mortar. The mortar plays an important role, as it is used to bond the blocks together.
However, the mortar mixture requires the correct ratio of sand and cement. Depending on how you mix the mortar, will depend on how many blocks you can lay.
When mixing mortar for concrete blocks, there are two common mixing ratios you will use. For jobs that need a stronger mortar, such as building retaining walls, you would commonly use a ratio of 3 parts sand to 1 part cement. However, for standard walls, you will usually use a ratio of 5 part sand to 1 part cement.
Using a mix ratio of 5:1, you will be able to lay around 500 blocks, which is enough to cover 50m2. This will use 1 tonne of sand and roughly 200kg of cement. If you are using a mix ratio of 3:1, it will enable you to lay 300 blocks, but you will require 333kg of cement.
How much cement will you need for 1 tonne of sand?
The amount of cement you need for 1 tonne of sand will depend on the mix ratio you use. Cement comes in bags of 25kg, which is a figure that is easy to work out how much you require.
It is important to understand how the amount of cement you need is calculated. If we opt for the mix ratio of 3:1, then this will mean, you use 3 parts sand and 1 part cement. So, the amount of sand you use will need to be divided by 3.
Now that we know what a bag of cement weighs, we can begin to work out how much cement we will require, and this is calculated like so:
1000kg (sand) divided by 3 = 333.33kg cement
So, we need a total of 333.33kg of cement. Now we need to work out how many bags of cement are required. To do this, we take this figure and divide it by the weight of a bag of cement:
333.33kg (cement) divided by 25kg = 13.33 bags. You would need to round this up, so a total of 14 bags are required.
For the mix ratio of 5:1, the calculations are as follows:
1000kg (sand) divided by 5 = 200kg cement
As we can see, we need a total of 200kg of cement. To work out how many bags you require, you divide this by the weight of a bag of cement:
200kg (cement) divided by 25kg = 8 bags of cement are required.
This calculation can be used to work out the amount of cement you need for any volume of sand.
Just take the volume of sand, divide it by the ratio mix (always use the bigger number) and divide the figure by 25kg (the weight of a bag of cement). This will provide the number of bags you require. However, always remember to round up the number so you aren’t short.
How long will 1 tonne of sand last bricklayers?
As we know, the mix ratio will determine how many blocks can be laid using a tonne of sand. The amount of time the sand will last, depends on how many blocks a bricklayer can lay in one day.
The number laid will depend on whether they are working alone or working in a gang. It will also depend on the mix ratio that they are using.
As we already know, 5:1 will produce more mortar, which will enable them to lay more blocks. Up to 500 per 1 tonne of sand.
Based on 500 blocks per 1 tonne of sand at a mortar ratio of 5:1, this will mean that a self-labouring bricky, should be aiming to lay around 100 to 150 blocks per day. This would mean that 1 tonne of sand will last between 3 and 5 days.
If you have a gang of two, which might include a bricklayer and labourer, then they can expect to lay up to 250 blocks per day. This will mean that a tonne of sand will last a maximum of two days
If we consider 300 blocks per tonne of sand, using a mix ratio of 3:1, then the sand will be used a lot quicker. For a self-labouring bricklayer, laying between 100 & 150 blocks per day, the tonne of sand will last for a maximum of 2 to 3 days.
Should a gang handle the job, then a tonne of sand won’t last much longer than one day, assuming they lay up to 250 blocks per day.
Conclusion
When laying concrete blocks, it helps to understand how many you can lay with a tonne of sand. It also helps to know how much cement you will need.
How long your tonne of builders sand lasts, is dependent on the mix you are using, as a ratio with more sand will produce more mortar. Whereas something like 3:1 will mean your sand lasts much longer, and you can lay more blocks.
