Why is PCC laid before Footing Works?

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Plain Cement Concrete, commonly called PCC or a “blinding layer,” is one of the first steps in foundation work. To many people on site, it looks like a simple layer of lean concrete placed before the actual footing is cast. 

Because it does not carry structural loads the way reinforced concrete does, PCC is often misunderstood as unnecessary or just a formality. In reality, PCC plays a critical role in ensuring the quality, accuracy, and durability of the foundation.

From an engineering perspective, PCC is not a structural element but a support layer that stabilizes the soil, protects reinforcement, improves construction accuracy, and creates a clean working surface for the footing. Without PCC, footing works become unsafe, imprecise, and vulnerable to soil contamination.

This article explains why PCC is laid before footing works and how it supports good foundation construction.

1. PCC provides a Clean and Level Base for Footings

Soil at the bottom of an excavation is rarely perfectly level. It may be uneven, soft, or disturbed by excavation tools. Casting concrete directly on such an irregular surface leads to:

1. Uneven footing thickness
2. Erratic concrete cover
3. Poor compaction
4. Material wastage

PCC creates a flat, hard, and uniform platform for the placement of reinforcement and shuttering. This ensures the actual footing dimensions match the structural drawings, improving accuracy and quality.

2. PCC prevents Soil Contamination of Structural Concrete

Fresh structural concrete must not be mixed with mud, loose soil, or organic matter. If the footing is cast directly on soil:

1. Cement paste gets absorbed by the ground
2. Soil particles contaminate the concrete matrix
3. Bonding at the bottom weakens
4. The footing loses strength

PCC acts as a barrier between the soil and structural concrete, preserving the designed strength of the footing.

3. PCC helps Maintain Correct Cover for Reinforcement

Reinforcement bars must have proper concrete cover to prevent corrosion. If bars are placed directly on soil:

1. Cover becomes inconsistent
2. Steel touches the ground
3. Moisture and chemicals attack the reinforcement

A PCC layer ensures reinforcement chairs remain stable and the correct cover is achieved throughout the footing.

4. PCC creates a Stable Platform for Reinforcement and Formwork

Footing reinforcement cages cannot be placed securely on loose soil. The weight of the bars often causes chairs or spacers to sink, leading to:

1. Misalignment
2. Variation in footing depth
3. Improper bar positioning

PCC provides a firm surface that supports chairs, shuttering, and reinforcement cages without movement during concreting.

5. PCC reduces Water Loss from Structural Concrete

Soil absorbs water. When footing concrete is poured directly on soil, the soil quickly draws water from the mix. This results in:

1. Reduced workability
2. Poor compaction
3. Weak zones at the footing base
4. Higher chances of honeycombing

PCC prevents this absorption, allowing the structural concrete to set under controlled moisture conditions.

6. PCC protects the Footing from Mud and Rainwater

During rainy or damp conditions, excavated pits are prone to:

1. Mud formation
2. Puddle water
3. Uneven softening of soil

PCC seals the base so that even if water enters the pit later, the footing can be cast safely without contamination or soil disturbance.

7. PCC acts as a Template for Footing Dimensions

Surveyors and site engineers use PCC as a reference base for:

1. Footing centrelines
2. Formwork alignment
3. Rebar positioning

Marking and layout become easier and more accurate on a solid PCC surface rather than on soil.

8. PCC helps Distribute Loads during Construction

Before casting the footing, the reinforcement and workers apply temporary loads to the base. On loose soil, these loads create:

1. Depressions
2. Soil deformation
3. Settlement under the reinforcement cage

PCC distributes these construction loads uniformly, preventing localized settlement and distortion.

9. PCC improves Site Safety and Workability

A stable PCC floor inside the excavation allows workers to move safely. Without PCC:

1. Workers slip on loose soil
2. Tools sink into the ground
3. Setting the formwork becomes difficult

This increases the risk of accidents and slows down work.

10. PCC prevents Direct Contact of Chemicals in Soil with Concrete

Some soil types contain sulphates or organic matter harmful to concrete. PCC acts as a protective layer, reducing chemical interactions between the soil and the structural footing.

11. PCC makes dewatering easier

If groundwater or rainwater enters the pit, a PCC floor prevents the base from turning muddy. Pumps can remove water easily without disturbing the soil below. This prevents delays and ensures footing works can continue smoothly.

PCC is a Low-Cost, High-Benefit Layer

PCC requires:

1. Lean mix (commonly 1:4:8 or 1:3:6)
2. Small thickness (50 to 100 mm)

Despite its low cost, it significantly improves the quality and reliability of foundation construction. Skipping PCC may save money initially, but it leads to poor workmanship, safety risks, and long-term structural issues.

When PCC is not   certain about advanced construction systems like raft foundations or bored piles, PCC may be replaced by:

1. Blinding layers of sand
2. Anti-termite treatment layers
3. Shotcrete blinding

However, these are carefully engineered substitutes. For most shallow footings, PCC remains the best and most economical option.

Frequently Asked Questions

1. Why is PCC required before laying footings?
To provide a clean, level, and solid base that supports reinforcement placement and prevents contamination of structural concrete.

2. What is the typical thickness of PCC under footings?
Usually 50-100 mm, depending on soil conditions and project specifications.

3. Can footings be cast without PCC?
Technically, yes, but it compromises quality. PCC prevents soil absorption, improves leveling, and ensures correct reinforcement cover.