How They Work
CPF liners are secured in place on vertical or inclined surfaces with staples or other fixing devices, having first been tensioned onto the formwork shuttering. Once attached concreting is performed in the normal way. Release agents are not required as CPF liners easily debond from the concrete during formwork striking.
Throughout the concreting process and as a result of concrete pressures, entrapped air and excess mix water that would otherwise become trapped at the surface causing blemishes, can instead pass through the liner. A proportion of this mix water is held within the liner and under capillary action, imbibes back into the concrete to assist curing. Liners generally have a pore structure that is designed to retain the majority of cement and other small fines.
This results (for vertical and inclined surfaces) in the creation a uniform surface relatively free from blowholes and other surface blemishes when compared to IMF concrete. But more importantly the achievement of a cover area with significantly enhanced durability.
Read more about this topic: Controlled Permeability Formwork
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