Yes, clay bricks do absorb water.
Understanding Water Absorption in Clay Bricks
Clay bricks are a porous building material, meaning they contain small voids or capillaries within their structure. These pores allow water molecules to enter and be held within the brick material, a process known as water absorption.
The degree to which a clay brick absorbs water is an important physical property that affects several aspects of its performance in construction.
Why Water Absorption Matters
Water absorption is not just a simple characteristic; it has significant implications for the durability and performance of brickwork.
- Bond Strength: As highlighted in the reference, the water absorption properties of clay bricks directly influence the strength of the bond formed with mortar.
It was found under laboratory conditions that, when clay bricks are being used, the strength of the bond varies according to their water absorption properties.
Mortar needs a certain amount of water to hydrate and cure properly. If a brick is too absorbent, it can rapidly draw water out of the mortar, leading to a weak bond. Conversely, if a brick is not absorbent enough, the mortar may not adhere well. This balance is crucial for stable and strong walls. - Flexural Strength: The reference also mentions that standards like BS 5628 provide guidance based on water absorption.
Thus for clay bricks, BS 5628 provides characteristic flexural strength values for various ranges of water absorption.
Flexural strength refers to the ability of brickwork (brick and mortar together) to resist bending forces. Different levels of water absorption require adjustments in mortar type or construction practices to achieve the desired structural performance. - Frost Resistance: When water absorbed by a brick freezes, it expands. This expansion can create internal stresses that may cause the brick to crack or spall (flake off). Bricks with high water absorption, especially those exposed to freezing temperatures, are more susceptible to frost damage.
- Efflorescence: Water moving through the brick can dissolve soluble salts within the brick or mortar. As the water evaporates from the surface, it leaves behind these salts, forming white, powdery deposits known as efflorescence.
- Thermal Performance: Water within the pores can affect the thermal conductivity of the brick, potentially reducing its insulating properties when wet.
Measuring Water Absorption
Water absorption is typically measured as a percentage of the brick's dry weight. Common tests involve immersing dry bricks in water for a set period (e.g., 24 hours) and measuring the weight increase. Another important measure is the initial rate of absorption (IRA), also known as suction, which indicates how quickly a dry brick absorbs water when placed in contact with it. This is particularly relevant for mortar bonding.
Standards classify bricks based on their water absorption levels, providing guidance on their suitability for different applications and exposure conditions.
| Water Absorption Level | Typical Percentage Range (Approx.) | Potential Implications |
|---|---|---|
| Low | < 10% | Good frost resistance, may need plasticizers in mortar |
| Medium | 10% - 15% | Suitable for most applications |
| High | > 15% | Higher risk of frost damage, requires careful mortar selection |
Understanding and managing water absorption is therefore essential for ensuring the longevity and structural integrity of clay brick construction.
