Common description
Red lead primer BS.2523, types A, B and C
Thixotropic red lead primer
Calcium plum- bate primer
Composition
Type A and B-red lead in linseed oil Type C-red & white lead in linseed oil
Similar, but with slight
modification to give a jel'y struc-
ture
Calcium plumbate as main pigment
Metallic lead primer
Fine
particles of metallic lead in vari- ous media
Zinc chromate and zinc tetroxy chromate primer
Chromated red oxide primer
Red oxide of iron primer
Zinc-rich primer ('cold galvaniz- ing')
Wash primers or etching primers
Zinc chromate as main pigment in various media
Mixture of zinc chromate and red oxide as pigment in various media
Red oxide as main pigment in various media
Fine particles of metallic zinc as pig- ment in chlorinated rubber or other medium
Primers, usually two-part, containing agents that etch the surfate of non- ferrous meta's to give a key
Table I compares the properties and uses of various priming paints for metals, including
including the long- established red lead and red oxide of iron paints as well as newer types. Undercoats and finishes
www.
Oil gloss finishes B.S.2525 to 2532
are now little used, their places having been taken by high gloss paints, based on drying oils combined with natural resins (oleore- sinous paints) or with synthetic resins (usually alkyd), offering marked improvement in gloss, dur- ability and other properties. Manu. facturers supply undercoat paints formulated to suit their own finishes and the use of these avoids the risk of incompatibility. It is advisable that there should be no prolonged delay between the application of the
86
Table 1
PRIMERS FOR METALS
Use
Priming iron and steel
Priming steel
iron and
Priming galvanized iron or zinc with- out need for etching, weathering or phos- phating; also useful on steel Priming steel
iron and
Priming aluminium; can also be used on iron and steel
Priming aluminium and steel
General-purpose pri- mer for meta's
Priming iron and steel
Priming non-ferrous metals without phos- phating or weather- ing, and sometimes
steel
Comments
The traditional primer for iron and steel and probably still best where preparation is
poor. Settles in the can to a hard cake and brushmarks do not level cut well; type C is better in these respects.
No settling in the can and reasonable freedom from brushmarks; on clean steel has similar per. formance to the traditional red lead primer, as far as experience goes..
The most convenient primer for galvanized iron on site: Also useful on steel, where its pale colour is more easily obscured by subsequent coats than that of red lead primers.
Can now be regarded as an established corrosion inhibiting primer for iron and steel.
Preferred if there may be long delay after priming. Especiai- ly valuable where chemical attack is likely. The main corrosion inhibiting primer for alum- inium; is also suitab'e for iron and steel, but perhaps less reliable for this purpose than other primers, especially on heavy steel. Those containing a substantial proportion of chromate are good corrosion-inhibiting primers.
These primers are less able than inhibitive primers to resist corrosion where the film is damaged, but are suitab'e for general use where conditions are not severe.
Inhibit corrosion of iron and steel, giving thick coats, but re'atively expensive. Less resistant to abrasion than hot-dip galvanizing, but more than most paints.
The preferred primer for flame-sprayed zinc and for aluminium on site, but except in mild con- ditions, a further coat of zinc chromate primer is necessary. Suitable for zinc and galvanized iron, but calcium plumbate primers are usually more convenient.
Some
undercoat and the finish. manufacturers advocate two coats of finish instead of one undercoat and one finish coat; this may give better durability, although at the cost of lower hiding power.
Varnishes
Varnishes based on synthetic re-
sins
as drying oils have largely replaced the natural oleoresinous varnishes formerly used, and for factory finished timber indoors (furniture, etc.) both have been replaced by cellulose or other sprayed lacquers.
The practice of applying varnish over flat paint to obtain a gloss finish has been discontinued because more satisfactory results can be ob tained by using modern high gloss paints. Varnishes nowadays are large-
ly used to obtain a gloss finish direct on timber. They are satisfactory for this purpose indoors but a varnished finish out-of-doors is far less durable than that afforded by painting, it is only on vertical surfaces, free from sharp edges, that it can be expected to last for more than a year or so and even then four or five coats will be needed to give a reasonable life. Although claims are frequently made for modern two-part varnishes, good quality yacht or spar varnishes gen erally give the best results on site.
On timber cladding where a high gloss is not required, the appearance can be preserved and the cost of treatment and maintenance reduced by applying, instead of varnish, a single coat of linseed oil fortified with paraffin wax and a fungicide. renewed when necessary,
THE HONG KONG & FAR EAST BUILDER-VOLUME 17, NUMBER 3
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