Dry Volume Of Cement Mortar: Everything You Need To Know

In this post, you’ll learn everything about the dry volume of cement Mortar.

There are some confusions regarding the dry volume of cement mortar.

Because calculating the dry volume of mortar isn’t the same as calculating the dry volume of concrete.

All of your confusion will eliminate after reading this post.

But, first…

What Is Cement Mortar?

It is just a mixture of Cement and Sand.

If you add coarse aggregate with mortar then it will become concrete.

What Is The Wet Volume Of Cement Mortar?

When water is added to the cement-sand mixture that is called wet mortar.

The volume we derived from the drawing is the wet volume of mortar.

What Is The Dry Volume Of Cement Mortar?

I think, you already get the idea.

That is, the quantity of a mixture of cement and sand before adding water is the dry volume of mortar.

The problem is, when you calculate the required mortar quantity for a specific work, for example, brickwork or plasterwork, you get the wet volume.

But if you want to know the required sand or cement quantity for the mortar, you need to convert that wet volume into the dry volume.

Don’t worry!

You can easily do that with the following formula:

Dry volume of mortar = Wet volume of mortar × 1.33

But, the question is…

What Is 1.33 In Mortar?

That is an experimental factor.

When water is added to the cement-sand mixture, it decreases in volume by 33%.

In other words, wet mortar increases by 33% in volume when it is dry.

That means, The dry volume of mortar is,

= Wet volume + 33% of wet volume

= Wet volume + (0.33 × Wet volume)

= Wet volume (1 + 0.33)

= Wet volume × 1.33

I think you’ve already understood the 1.33 factor for calculating the dry volume of mortar.

Then, let’s see an example on…

How To Calculate The Dry Volume Of Cement Mortar

Suppose, you’re going to plaster (¾″ thick) on the following wall surface:

The required mortar quantity for this surface is,

= Length × Width × thickness

= 10′ × 10′ × ¾″ [¾″ = 0.06 feet]

= 6 cubic feet

This is the wet volume of mortar.

If you want to calculate the required cement and sand for this mortar, you first need to convert that wet volume into the dry volume.

Let’s do that.

The dry volume is,

= Wet volume × 1.33

= 6 × 1.33

= 7.98 cubic feet.

This is the required dry volume of mortar for our plastering surface.

Let’s say, you are using 1:4 cement-sand ratio for preparing mortar.

With that, you can now…

…Calculate The Required Cement

The formula is,

= (Dry volume of mortar ÷ Sum of ratio) × Cement ratio

= (7.98 ÷ 5) × 1

= 1.59 cubic feet.

If you want to convert this cement volume into bags…

= 1.59 ÷ 1.25 [1 bag cement = 1.25 cubic feet]

= 1.27 bags.

Applying the same formula above, you can also…

…Calculate The Required Sand Quantity

That is,

= (Dry volume of mortar ÷ Sum of ratio) × Sand ratio

= (7.98 ÷ 5) × 4

= 6.38 cubic feet.

Conclusion:

I’ve seen many construction professionals using the factor 1.54 to get the dry volume of cement mortar.

But that factor is used for concrete, not for mortar.

Make no mistake.

Always use 1.33 for calculating the dry volume of mortar.

Your Turn:

After adding water, sand volume decreases about 20% — 27% and cement volume doesn’t decrease due to fine particles.

My question is, why do we consider 33% decrease for cement mortar?

Do you have any idea?

Please share your opinion in the comments below…