We need to calculate the dry volume of mortar whenever we want to know the required quantity of cement and sand for preparing mortar for our masonry work.
Nowadays, cement mortar is mostly used for all types of masonry work.
When we estimate the volume of mortar for various masonry work, we just get the wet volume. But, to get the required cement and sand volume we need to convert that wet volume of mortar into the dry volume.
first, we need to understand what is the dry volume of mortar?
What is The Dry Volume of Mortar
The main ingredients of mortar are cement and sand.
Adding water to the dry mix of cement-sand, mortar is prepared.
When water is added to the dry mix of cement-sand, the volume of dry mix is reduced. It happens due to the presence of air voids in sand particles.
When we calculate the mortar quantity for any masonry work, we get the wet volume of mortar. If we want to calculate the required volume of sand and cement, we need to convert that wet volume into the dry volume.
How to Get The Dry Volume of Mortar From Wet Volume
As mortar volume is increased in dry conditions, we need to multiply the wet volume by 1.30 to get the dry volume of mortar.
But the question is how do we get the 1.30?
What is The 1.30 For Calculating The Dry Volume of Mortar?
In dry condition, sand particles contain air voids. So, when water is added to the dry sand, the volume of sand is reduced. It is happened due to the presence of air voids in sand particles. The percentage of air void compressibility of sand is somehow 20% to 27%.
We normally take the highest percentage of air void compressibility of sand when converting the wet volume into the dry volume. That is 27%.
Due to the very fine particles of cement, the air void compressibility of it is ignored.
So, the wet volume of mortar is actually 27% increased in dry condition. But, the sand isn’t used at a time for preparing mortar. mortar is normally mixed in various places in the building. So, some portion of sand is wasted which isn’t normally happened in mixing concrete. that is the reason we normally calculate 3% wastage of sand for mortar which isn’t taken for calculating sand for concrete.
If we add this 3% wastage to the percentage of air void compressibility of sand, it will be 30% (27% + 3%).
So when we calculate the dry volume of mortar, we just multiply the wet volume by 1.30.
That is 100 unit of wet mortar will actually be 130 unit in dry condition.
Let’s see a practical example.
A Practical Example of Calculating The Volume of Cement and Sand in Mortar
When we estimate the mortar quantity for any masonry work, we just get the wet volume of mortar.
Let’s assume we require 10 cubic feet wet mortar and the ratio of cement and sand in the mortar is 1:4.
Now we’ll see how we can calculate the dry volume mortar and then sand and cement quantity for this 10 cubic feet mortar.
Get The Dry Volume of Mortar
As we discussed above, the dry volume of mortar is,
= Wet volume of mortar x 1.30
=10 x 1.30
=13.00 cubic feet.
Calculating Cement And Sand Volume in Mortar
The ratio of cement and sand in mortar is 1:4. That is one unit of cement will be mixed with four units of sand.
Total units of ingredients in mortar are 1+4=5.
So, the required volume of sand for our proposed mortar quantity is,
= (13.00 ÷ 5) × 4
= 10.40 cubic feet.
And required cement quantity is,
= (13.00 ÷5) x 1
= 2.60 cubic feet.
To calculate the dry volume of mortar, you just need to estimate the wet volume of mortar for your work item and then multiply that wet volume by 1.30.
Once you get the required dry volume of mortar, you can then calculate the required cement and sand quantity for the mortar based on the mix proportion.