Dry Volume and Wet Volume in Concrete and Mortar
In this post, you are going to learn the difference between wet volume and dry volume of concrete and mortar and how you can use it to estimate the quantity of building materials required.
ESTIMATION
Understanding Dry Volume and Wet Volume in Concrete and Mortar
Table of contents
Core Concept or Idea
What is dry volume and wet volume?
What is 1.54 in concrete and 1.33 for mortar?
Dry Volume and Wet Volume in Concrete
Dry Volume and Wet Volume in Mortar
Recap of Key Formulas
Core Concept or Idea
In construction and civil engineering, knowing how to estimate building materials such as cement, sand, and aggregates is essential. One of the key concepts that every civil engineer, quantity surveyor, or even a DIY individual should understand is the difference between dry volume and wet volume. These terms play a huge role in determining how much material is needed for any given project.
Let’s break down what these terms mean, why they are important, and how you can use them to make your material estimations more accurate.
What is dry volume and wet volume?
Quite simply, dry volume refers to the volume of materials like cement, sand, and aggregates in a dry state, without any water added. On the other hand, wet volume refers to the same materials with water added.
In construction, whether you're casting concrete or mixing mortar, the mixture will reduce once water is added, and this is because the air gaps in dry materials are filled, resulting in a smaller volume.
Importance of dry volume and wet volume
When planning, it’s important to account for the change in volume. If you only estimate material requirements based on wet volume, you’ll end up doing an underestimation, meaning delays and added costs when estimating. When making a bill of quantities, we have to keep in mind that the concrete that we cast on a slab is wet volume, but the materials that we purchase are dry volume.
Below is the shrinkage that occurs when water is added.
What is 1.54 in concrete and 1.33 for mortar?
Concrete (cement + sand + aggregates) reduces by 54%.
Mortar (cement + sand) reduces by 33%.
These figures are reliable constants used globally in the construction industry, and using these, you can accurately convert between dry and wet volumes when calculating how much material you need.
Dry Volume and Wet Volume in Concrete
Concrete is a mixture of cement, sand, and aggregates. When it's in its dry form (before water is added), it occupies more space. As mentioned, once water is added to the mix, the volume reduces by around 54%.
The formula for converting wet volume to dry volume in concrete is straightforward:
Dry Volume = Wet Volume × 1.54
The 1.54 constant accounts for the 54% shrinkage.
Example:
Imagine you need to cast concrete for a slab with a 100 cubic metre (m³) wet volume. You’ll need more than 100 m³ of dry materials to get that final volume once water is added. Using the formula above:
Dry Volume = 100 m³ × 1.54 = 154 m³
This means you'll need 154 cubic metres of dry mix to end up with 100 cubic metres of concrete.
Example 2.
Imagine you need to cast concrete for a slab with a 500 cubic metre m³ wet volume. You’ll need more than 500 m³ of dry materials to get that final volume once water is added. Using the formula dry volume = wet volume x 1.54
Dry Volume = 500 m³ × 1.54 = 770 m³
This means you'll need 770 cubic metres of dry mix to end up with 500 cubic metres of concrete.
Dry Volume and Wet Volume in Mortar
Mortar is typically a mixture of cement and sand, often used to build masonry walls, that is, bricks or blocks. When water is added to mortar, the volume reduces, but not as dramatically as concrete. The volume decreases by 33%
To convert wet volume to dry volume of mortar, the formula is as follows:
Dry Volume = Wet Volume × 1.33
The 1.33 constant represents that 33% shrinkage you should expect.
Example:
Let’s say you're working on a mortar project with a wet volume of 100 m³. Using the formula for mortar:
Dry Volume = 100 m³ × 1.33 = 133 m³
This tells you that to get 100 m³ of wet mortar, you’ll need 133 m³ of dry materials.
Recap of Key Formulas
When converting between dry and wet volumes in construction projects, these essential formulas will serve you well:
For concrete, multiply the wet volume by 1.54 to get the required dry volume.
For mortar, multiply the wet volume by 1.33 to convert it into dry volume.
For example, if you're laying a concrete slab, you’ll be casting wet concrete. But when calculating how much cement, sand, and aggregate to order, always base your order on dry volume to account for the reduction in size when water is added.
Understanding dry volume versus wet volume is a simple but critical part of any construction project. Once you understand how much the volume decreases when water is added, you can plan your material needs accurately. By using the constants 1.54 for concrete and 1.33 for mortar, you’ll have a foolproof way to convert between these two volumes.
I made a video version about dry volume and wet volume. click here to watch it