Preparing Iron Work for Painting
Corrosion in generally more rapid and severe in hidden places and pockets where water or rubbish collects. It is however, most severe in surfaces of steel or iron in contact with wood ; water is bound to collect between the wood and iron. Before painting, rust scales and dirt should be removed by means of iron brushes can be used for removing the loose dust. Bristle or wood fibre brushes can be used for removing the loose dust. Special attention should be given to the cleaning of corners and re-entrant angles. Oil and grease can be removed by gasoline (petrol) or benzene excess of which shall be wiped oil off from the surface.
Flame cleaning is another method of preparing the surface. A flat oxy-acetylene flame is passed over the metal burning off the old paint and loosening the rust and scale and wire brushing. A solution of country soda and fresh slaked lime in equal parts will remove old paint from iron-work. 40 kg is enough for about 75 sq.m of surface area.
Paints containing red lead and litharge have been in use for a very long time and have given excellent results. There is nothing to compare with red lead for a priming or under-coat on structural steel where there is no abrasion, and is said to be very durable when pure. Red lead primer followed by a finishing coat of red oxide paint or paints with aluminium or graphite bases have been found very satisfactory. (Red oxide is grouped up with boiled linseed oil) Red lead guards against rust while white lead and red oxide of iron do not stop rust. White lead applied directly to iron requires incessant renewal and probably exerts a corrosive effect. It may however, be applied over the more durable paints when appearance require it.
The first coat can be a mixture of pure linseed oil and dry red lead in the proportions of 1:5 liters of oil to 15 kg of red lead. It should be applied immediately after cleaning the surface of the metal and when the metal is perfectly dry. If the coat is rained upon within 24 hours of application it must be removed and another coat applied. The second coat will be applied when the first coat is thoroughly dry and set, which will be in about 4 days and may consist of :3 kg of red oxide paint; ½ kg of lamp black; 5 liters of boiled linseed oil.
The third coat can be of : 3 kg of red oxide paint ; 5 liters boiled linseed oil.
For unimportant iron works, or for roofs, red oxide paint can be made as follows :
