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Lift lines

Lift lines (sometimes referred to as pour lines) appear as colour changes along the boundaries between successive lifts within a pour.  Can mistakenly be referred to as cold joints.

Lift lines are typically caused by a slight change in w/c ratio between each pour/batch and darker fine material being brought to the surface with the bleed water before the subsequent pour is placed.

To reduce the likelihood of it occurring ensure;
 - consistency in the concrete supply, 
 - the concrete is well mixed, 
 - the pour concrete at a lift rate of not less than 2m rise per hour, 
 - the time between placing batches is minimised.

Acknowledgement: Concrete Society

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Cold joints

Pour lines and shadow marks

Visual Concrete: Control of blemishes