A film layer is the thin, continuous coating of paint, lacquer or coating that remains on a substrate after drying or curing. The film layer is the actual protective and/or decorative layer. Its thickness is usually between a few micrometres (µm) and several millimetres, depending on product and application.
Function of the film layer
A good film layer fulfils several tasks:
Protection
- Against moisture — sealed surface prevents penetration
- Against UV radiation — protects wood and plastic substrates
- Against mechanical wear — wear-resistant top coat
- Against chemical attack — resistant to acids, bases or salts
- Against corrosion — passive protection of steel
Finish
- Colour — aesthetic appearance
- Gloss — matt, satin or high-gloss
- Texture — smooth, structured or relief
Composition of a film layer
The dry film layer consists of:
- Binder — forms the film skeleton (alkyd, acrylic, epoxy)
- Pigment — colour and opacity
- Fillers — volume and properties
- Additives — improve flow, adhesion and stability
During drying, solvents or water evaporate and the film layer remains.
Application
Film layers occur in many construction applications:
- Painting — exterior frames, façades, doors
- Floor coatings — epoxy floors in industry
- Roof coatings — liquid roofing
- Road markings — durable wear-resistant paint
- Structural steel — corrosion-resistant paints
- Wood protection — stains, lacquers, varnishes
Dry film thickness (DFT)
Dry film thickness (DFT) is measured with a coating thickness gauge. For different systems:
| Application | DFT (µm) |
|---|---|
| Indoor wall paint | 30–50 |
| Exterior paint | 60–120 |
| Floor epoxy | 150–500 |
| Corrosion protection system | 200–600 |
| Liquid roofing | 1000–3000 |
A film layer that is too thin gives inadequate protection; one that is too thick can crack or adhere poorly. Manufacturers therefore specify exact spread rates and thicknesses.
Related terms
- Coating
- Primer
- Adhesion
- Pigment
- Hydrophobic treatment
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