Excess water that appears on the surface of concrete after it has been placed and begins to settle is commonly known as bleed water. Removing this bleed water is crucial for achieving a durable and strong concrete surface.
Understanding Bleed Water in Concrete
Bleed water occurs as heavier solid particles (like cement and aggregates) settle downwards, displacing some of the mixing water upwards. This is a natural process, but excessive bleed water or improper handling can weaken the concrete's surface layer.
Effective Methods for Removing Bleed Water
Handling bleed water depends largely on the stage of the concrete's setting process. The key is often patience, but sometimes active removal is necessary.
After Concrete Placement and Initial Setting
If you have already laid the concrete and begun the curing process but you notice bleed water on the surface, it's important to remove it before finishing or curing continues. The reference provides specific methods for this scenario:
- Cleaning it up using cloths: Absorbent materials like cloths can be used to gently soak up and remove the pooled water from the surface.
- Draining it with a pump: For larger areas or significant amounts of bleed water, a small pump can be effective in drawing the water off the surface.
Important: When using these methods, be careful not to disturb the concrete surface itself or remove any cement paste along with the water.
Before Finishing Operations
Typically, concrete finishing (like floating or troweling) should not begin until the bleed water has either evaporated or been removed. The most common approach at this stage is to wait for the bleed water to dissipate naturally.
- Allowing Evaporation: In suitable weather conditions, the bleed water will evaporate from the surface. This is often the preferred method as it avoids disturbing the mix.
- Avoid Rushing: Do not attempt to "work in" bleed water back into the concrete surface with finishing tools, as this dilutes the cement paste at the top, leading to a weak, dusty, or scaled surface.
Why Bleed Water Removal is Important
Properly addressing bleed water prevents several issues:
- Weak Surface: If trapped or worked back in, it dilutes the cement paste, creating a weak top layer prone to dusting and scaling.
- Poor Bond: It can hinder the bond of subsequent layers or surface treatments.
- Increased Permeability: A weakened surface can be more susceptible to water penetration.
Handling bleed water correctly ensures the concrete cures properly and achieves its intended strength and durability.
