It is a good idea to note typical surface temperatures when selecting paints radiators, steam pipes, boilers, metal chimneys, etc. This information relates to the temperature a given paint is capable of withstanding without discolouring or breaking down and helps your paint supplier to recommend the correct paint for the job.

Discolouration usually occurs as a darkening of the medium when subjected to heat, and the degree of darkening will vary according to the type of medium and the temperature to which it is subjected. A paint film may discolour to a marked degree yet still provide a protective coating to the surface onto which it has been applied. However, this discolouration can spoil a colour scheme, or affect an "identification colour" to the extent that a dangerous error could occur through wrong identification during maintenance work.

Apart from the actual resistance of a paint film, it should be noted that the radiation and heating efficiency of a hot water or steam heating system depends upon the type of paint applied to the radiators and heating pipes. Bright metal surfaces, aluminium paint, bronze paints and gloss enamel paints give minimum radiation, whilst matt finishes and metal surfaces in a rusty condition give maximum radiation.

Radiation varies considerably in relation to the glossiness or dullness of the surface regardless of the type of paint applied to its surface.

The method of painting radiators and hot water pipes should be to keep the elasticity of the film build-up as similar as possible, otherwise unequal expansion of the different coats in the paint film might cause cracking and subsequent flaking. This may be achieved by the use of a good adhesive primer such as Zinc Phosphate Primer, followed by two coats of the required finishing material (i.e. omitting an undercoating in the case of gloss finishes).

Before priming, the metal should be thoroughly prepared to remove all rust, dirt and loose material. It should then be subjected, if possible, to mild heat 38 oC (approx 100 oF) to dry off any moisture which

has condensed on the surface and in the pores of the metal, and the primer applied whilst the metal is still warm.

Special heat resisting paints do not require primers, as these may disintegrate at lower temperatures than the finishes themselves, but it is absolutely essential that the metal is perfectly clean and dry before the paints are applied.

When choosing paints for particular purposes in industry, their particular properties should be considered in order to maximise the use of the paint.