Materials such as composite decking, factory made aluminium, fibre glass trim and vinyl siding are some materials that do not require frequent maintenance and hence do not require repainting.
However they can be repainted if one wishes to change the colour or appearance of the material. Before starting the repainting process, it is necessary to carry out the required repair procedures such as cleaning and rinsing the surface, removing mildew and using a 3:1 water/bleach solution.
Another recommendation made by paint and colour expert Debbie Zimmer from the Paint Quality Institute, is that top quality acrylic latex primer be used when maintenance free materials are to painted. A high quality primer will help the paint to stick to the surface better and will give a better finish and sheen to the surface. Likewise, the paint too must be high quality 100% acrylic latex paint especially for maintenance free surfaces that are thick and smooth. A good quality acrylic latex paint will provide good adhesion and ensure that the surface has the same appearance for years to come. Primer and paint should be applied with rollers and brushers that are of good quality and should be applied under moderate weather. Extreme weather conditions may have a negative effect on the manner in which the paint dries and thus affect the quality of the coating.
Source: http://www.paintquality.com