Edge Rippling of Film Faced Plywood

Rippling is normal natural swelling of wood or film faced plywood in a short time.

Edge rippling occurs on plywood frequently especially when the formwork plywood is used in heavy rain and harsh sunshine after rain. Plywood swells around the drilled holes too. These should be considered natural and not problematic.

film faced plywood edge rippling
Film faced plywood edge rippling which will disappear after 48 hours

Change of Plywood Moisture Content

The double-faced film faced plywood has a moisture content ratio of 25-30% in use. It can creat a smooth concrete finish in the formwork. But the film faced plywood at the factory has a very low moisture content. The M/C can be as low as 8% when they are packed by the manufacturer.

In the first few casting, the moisture are going into the plywood little by little.

In the drilled holes and cutted edges, the water goes into plywood faster than the film faces. This cause uneven results in different part of the plywood sheet.

After 3-5 concrete forming, the moisture content of film faced plywood rise from 8% to 27%. The film wrinkles and swelling disappear. During the process, the rippling won’t affect the concrete shuttering very much.

Vessels in Hardwood Veneers

Vessels are like thin and long pipes in the hardwood. In a tree, vessels transport water along grain direction.

Face veneer of film faced formwork plywood

face veneer of film faced plywood

Face veneer absorbs water in the concrete and cause rippling of film face. It absorbs water in every directions but it absorbs the most water in the vessels direction.

Rippling

Rippling appears when dry plywood absorbs water through some small damage on the phenolic film or edges in short time.

Water moves along a vessel. Wood around the vessel gets wet.

Rippling steps:

  • Dry plywood absorb water through a small damage or edges in film face.
  • Water is transported by a vessel along grain direction.
  • Wood around vessel gets wet and swells. Rippling appears.
  • Later moisture is balanced in the plywood and rippling goes down.

Edge Rippling

Edge rippling appears when dry plywood absorbs water from edges. Areas around vessels swell first. Later moisture is balanced in plywood and edge rippling goes down.

1. Edge of plywood absorbs water

edge rippling film faced plywood 6 hours

2. Wood around vessels swell first (edge rippling)

edge rippling film faced plywood 24 hours

3. Moisture is balanced in the plywood and rippling goes down

edge rippling film faced plywood 48 hours

How to minimize the “rippling” effect?

As we know the rippling is caused because of the low moisture content of plywood. So in order to reduce the rippling effect, the phenolic film should be treated prior to first use.

How to do it?

Formwork workers will need to apply a wet cement slurry or grout wash on the plywood surface. The plywood edge swelling on the film will become less noticeable.

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