How To Calculate Shuttering Quantity For Slab

How To Calculate Shuttering Quantity For Slab

In this post, you’ll learn how to calculate the required material for slab shuttering.

Depending on the availability, you can use a combination of various types of materials for your slab.

I’ll show you the method of calculating the shuttering materials. It’s upon you that require to decide which materials you’ll use.

So let’s learn the process.

How To Calculate Shuttering Quantity For Slab?

Step-1: Get The Slab Layout Drawing

In your project, you’ll have a slab layout drawing in your structural drawing book like this:

Slab layout plan

This is an example of a slab layout plan with beams.

It’s a common practice to construct slabs and beams simultaneously in residential buildings.

I’ve discussed the calculating process of beam shuttering materials before. So in this post, I’ll just show you how to calculate the required quantity of slab shuttering materials.

For that…

Step-2: Divide The Slab Into Panels

A slab portion surrounded by beams is called a panel.

If we divide our example slab layout into panels it’ll look like this:

Slab layout plan with panels

With this, let’s…

Step-3: Calculate Sheathing Materials

For that:

First, Get the dimension of the panels.

If your slab layout plan doesn’t have dimensions on it, get it either from the column layout plan or from the architectural plan.

Once you get the dimension, it’ll somehow look like the image below:

Slab panels with dimensions

Next, calculate the total area of the panels.

Here,

  • Panel-1 = 19′-7″ × 9′-8″ = 189.33 sq.ft
  • Panel-2 = 19′-7″ × 9′-4″ = 182.68 sq.ft
  • Panel-3 = 4′-11″ × 3′-11″ = 19.28 sq.ft
  • Panel-4 = 4′-11″ × 15′-1″ = 74.19 sq.ft

So, the total panel area is,

= 189.33 + 182.68 +19.28 + 74.19

= 465.48 sq.ft.

After that, Calculate the area of a sheathing board.

As a sheathing board, you can use plywood or plain sheet.

Let’s say, you’ll use ¾″ thick plywood and the size of plywood is 3′ × 6′.

So, the area of a plywood board is,

= 3′ × 6′

= 18 sq.ft.

Next, Calculate the number of required plywood boards for panel-1.

And, the formula is,

= Area of panel1 ÷ Area of a plywood board

= 189.33 ÷ 18

= 10.51 nos

Say, 11 nos.

Now, calculate the required quantity of plywood per square foot.

The formula is,

= Required number of plywood for panel1 ÷ Area of panel1

= 11 ÷ 189.33

= 0.058 nos/sq.ft.

Finally, Calculate the required plywood for all the panels.

And, the formula is,

= Required plywood per square foot × Area of all the panels

= 0.058 × 465.48

= 26.99 nos

Say, 27 nos.

Step-4: Calculate The Quantity Of Cleats

Slab’s sheathing materials rested upon cleats.

As cleat, you can use 1½″ × 1½″ MS hollow boxes or 1″ × 4″ wooden lumber.

As we are using ¾″ thick plywood, we can use cleats on 2-feet centers.

Distance between cleats in slab shuttering

To calculate cleats…

First, Get the dimension for slab panel-1.

Dimension of a slab panel

We’ll place cleats along the width of the panel.

Next, calculate the required number of cleats.

The formula is,

= (Length of the panel ÷ Distance between cleats) + 1

= (19′-7″ ÷ 2′-0″) + 1

= 10.79 nos.

Say, 11 nos.

After that, calculate the required quantity of cleats for panel-1.

And,

The formula is,

= Length of a cleat × number of cleats

= 9′-8″ × 11

[Length of a cleat is equal to the width of the panel.]

Calculating the length of a cleat in slab shuttering.

= 106.37 running feet.

Say, 107 running feet.

Now, calculate the required cleats per square foot.

The formula is,

= Required cleats for panel1 ÷ Area of panel1

= 107 ÷ 189.33

= 0.565 running feet/sq.ft.

Finally, calculate the total required cleats for all panels.

And,

The formula is,

= Required cleats per square feet × Area of all panels

= 0.565 × 465.48

= 262.99 running feet.

Say, 263 running feet.

[Note: If you use plain sheets instead of plywood, you’ll need more cleats. In that case, we normally use cleats on 6-inches centers.]

Step-5: Calculate The Quantity Of Joist

Joists are used below cleats on 4-feet centers.

Example of joists in slab shuttering

Depending on the thickness of the slab, 2″ × 4″, 2″ × 6″ or 4″ × 4″ MS hollow box or wooden batten is used as joists.

Let’s say, we’ll use 2″ × 4″ MS hollow boxes.

To get the required quantity of joist…

First, calculate the required number of joists.

The formula is,

= Width of the panel ÷ Distance between joists

= 9′-8″ ÷ 4′

= 2.41 nos

Say, 3 nos.

Next, calculate the required joist quantity for the panel.

And, the formula is,

= Required number of joists × Length of a joist

= 3 × 19′-7″ [Length of a joist is equal to the length of the panel]

= 58.74 running feet.

Say, 60 running feet.

Now, calculate the required joist per square foot.

The formula is,

= Required joists for the panel1 ÷ Area of the panel1

= 60 ÷ 189.33 [we calculated the panel area in the step-3]

= 0.317 running feet/sq.ft.

Finally, calculate the total required joists for all the panels.

And, the formula is,

= Required joists per square foot × Total area of the panels

= 0.317 × 465.48 [We calculated total panel area in the step-3]

= 147.55

Say, 150 running feet. [Round number is taken here]

Step-6: Get The Quantity Of Required Props

Props are used below joists on 2-feet centers along the joist.

You can use steel props, bamboo, or scaffolding for this purpose.

Let’s say you’ll use steel props.

To calculate the required props…

First, Get the total length of joists for all panels.

We have calculated this in the above step.

And, that is 150 running feet.

With that:

Now, calculate the required quantity of props.

The formula is,

= Total length of joists ÷ Distance between props

= 150′ ÷ 2′

= 75 nos.

[Note: If you use scaffolding instead of props, the distance between scaffoldings should be 4 feet. In that case, use 4′ instead of 2′ while calculating the above formula.]

That’s it.

Summary:

  • ¾″ thick plywood (3′ × 6′) = 27 nos
  • 1″ × 4″ wooden lumber = 262 running feet
  • 2″ × 4″ MS hollow box = 150 running feet
  • Steel props = 75 nos

Editor’s Note: This post was originally published in July 2021 and has been updated for accuracy and comprehensiveness.

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