Medium-density fiberboard, or MDF, is low-cost and easy to work with. A plain MDF surface, however, is rough and does not hold up well to water damage. MDF is often coated in vinyl or a similar hard material to protect the core MDF material from wear and tear. If you're working with a plain MDF surface, emulsion paint is a good way to seal and protect the surface. Apply emulsion paint straight onto the MDF, as the synthetic resin will form a tough, weather-resistant coating.
Wipe dust and dirt from the surface with a moist rag. Fiberboard surfaces don't tolerate moisture-damage well, so don't saturate the rag; wet it just enough to pick up dirt from the surface.
Apply emulsion paint straight onto the MDF surface, using a synthetic-bristle paintbrush or a heavy-nap roller. Brushes are best for smaller MDF items, while rollers speed up large paint jobs. When you apply the paint, allow about 50 per cent overlap between each brush stroke or roller line.
Paint the MDF with a second coat of emulsion paint after the first coat dries. Even if the first coat provided good coverage, a second coat is a good idea to provide a thicker weather-resistant coating. Do not use the MDF surface until 24 hours after the last coat dries.