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I
063
IRON AND STEEL
Iron and Steel are the most used metals in our civilized society but are very
prone to corrosion even in ordinary normal atmosphere; hence need protection
from decay and disintegration. Painting is the most easy and cheapest way of
protecting iron & steel but proper protection cannot be achieved unless surface
preparation of the highest order is done before painting.
Surface Preparation:
Excellent surface preparation can be done by such mechanical means as shot,
grit or sand blasting, flame cleaning, impact needle guns. Other mechanical
means normally used are chipping, scrapping, wire brushing & emery rubbing.
Various forms of chemical cleaning are also adopted. The whole essence of
surface cleaning is that surface should be a clean bright metal free from rust,
dust and oily matters.
When any steel structure comes in CKD condition with steel parts pre-primed
check for fine blisters. If observed, it can be assumed that the metal is already
affected by corrosion underneath the primer. In that case the primer has to be
removed and surface prepared to bright metal & primed again. For any
mechanical damage spot priming can be done with surface preparation.
Painting:
The prepared surface must be primed with a suitable primer depending on
atmosphere & activity within one hour or as early as possible. After surface
preparation if left out unpainted for a longer time moisture in air can produce
infinitesimal rust not recognizable by naked eye.
Primer:
One coat of suitable rust inhibitive primer-Red Oxide, Red Lead, Zinc Chromate,
Zinc Phosphate Primer.
Finishing:
2 coats of suitable enamel paint either glossy or matt finish.
Note: Primers and top finish coat have to be selected depending on the type of
protection needed considering environment, atmosphere, weather condition and
activity. It is better to apply top coat, at last one, without leaving primed surface
for a longer time.
064
INSULATION BOARDS
(See ‘Building Boards’)
Painting:
1 coat of Plastron Sealer or Bison Primer
2 – 3 coat of Robbialac Acrylic Plastic Emulsion or Luxury
                                    Silk.