No_3_October_1962 — Page 90

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

Page 90Page 91

IPCO

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CRYLIC EMULSION

SUND PAINTCO/

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An Empire Rodent IMAND PAINT CO./

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