Grain Raising or Surface Swelling
Grain raising is caused by moisture penetrating the phenolic surface film and causing
swelling of the surface veneer.
The causes of grain raising are:
- Severe weather exposure
- Failure to use release agent or form oil
- Damage to the phenolic surface film i.e. misuse of vibrators, handling damage
etc. - Faulty phenolic surface film
As mentioned previously, the purpose of the phenolic surface film is to minimise moisture
penetration of the surface veneer.
Note that the phenolic surface film is not “water proof” and only slows the penetration of
moisture to an extent that grain raising becomes manageable.
The use of form oil and release agent is critical to prevent grain raising.
No formply manufacturer guarantees a Class 2 surface finish where a release agent has
not been used.
The effectiveness of the phenolic surface film is greatly enhanced by the application of
form oil.
An additional significant cause of grain raising is damage to the phenolic surface film
through careless use of vibrators, handling on site and especially damage from handling of
the steel work (See Plate 5).
A damaged surface layer is an entry point for moisture and rapidly leads to severe grain
raising. The use of a release agent immediately prior to pouring is effective in minimising
moisture penetration by sealing scratches and damaged areas of the surface film.
However, most grain raising is associated with weather exposure. In severe weather
conditions, it is practically impossible to eliminate moisture penetration of the surface
layer and some grain raising.
In such weather conditions, tarping of the deck to fully protect against weather exposure is
the only practical method to prevent both grain raising and distortion.
