Rendering articles

The original Mediterranean villas in Europe were externally rendered and painted white to help reflect heat from the Sun during the Summer season, the white pigment of the paint being due to  titanium dioxide

A rendered finish is generally guaranteed to provide protection of the duration 15-20 years if properly applied while the addition of paint further protects the external render from the damage caused by the weather.

However, the application of paint to rendered surfaces is difficult and required practice as it is essential to keep the correct proportion of colour additives when painting on to the rendered surface. If an incorrect proportion of colour additives is applied, the result will be noticeable patches of paint on the external walls. Added to that problem is that even if you manage to accomplish an even finish on the externally rendered surface, the colour oxides can sometimes fade quickly, losing their ability to reflect coloured light a a high frequency because the colour oxide pigment molecules have been spread out too thinly on the paint mixture.  If rising damp or any damp condition is present, the colour oxides can appear in the areas where there is sunlight and hence less evaporation occurring.

Note: a colour pigment is

• a fine particle which is remains mostly undissolved in the paint medium and its purpose is to provide colour to lime based building materials.
• does not react with the other constituents in a rendered mix
• alkali resistant ( i.e. resistant to environments which have a low Hydrogen proton concentration)
• able to retain their colour in an alkaline environment such as the Ca(OH)2 environment in mature lime putty
• highly resistant to decomposition from the action of high energy ultra violet radiation
• usually derived from inorganic materials
• able to coat the cement and sand particles of a render mix.
• uniformly distributed throughout the mix
• based on oxides and hydroxides of iron and these are used to
  produce various shades of red, yellow, brown and black. Oxides of chromium ( Cr(III) ions) are used to produce green colours, compounds of cobalt are used to produce blue colours. Also, oxides of aluminium, nickel and antimony are also used often in combination with other metallic oxides.

A house that has been rendered and painted will have clean, smooth lines and precise corners. It is recommended that prior to applying the paint on the external render or preferably when consulting an architect on the design of the property that a smooth external render should be applied followed by the painted finish to achieve a nice, smooth finish.

Another use for painting rendered surfaces is in situations where the brick walls have been severely damaged or repairing the brick walls will not fully restore them.