Indian Raod cngress

Section 1900
Structural Steel
The primer, intermediate and finishing coats shall all be applied so as to provide smooth
coatings of uniform thickness. Wrinkled or blistered coatings or coatings with pinholes,
sags, lumps or other blemishes shall not be accepted. Where the Engineer so directs, the
coating shall be removed by abrasive blast cleaning and replaced at the Contractor’s
cost.
1906.7 Protective Coating System in Different Environments
Since the seriousness of the problem of corrosion depends upon atmospheric conditions
and these vary enormously, there is no single protective system or method of application
that is suitable for every situation.
However, as a guide, broad recommendations are given in Table 1900-3 for various types
of coatings in various environmental conditions which should be complied with.
Approximate life to first maintenance is also indicated and can be used as a guide.
Table 1900-3 Recommendations for Types of Protective Coatings
System
Environment
i) Wire brush to remove all loose rust and Suitable for mild conditions where
scale; 2 coats drying oil type primer, appearance is of some importance and
1 under coat alkyd type paint; 1 finishing where regular maintenance is intended.
coat alkyd type. Total dry
This system may deteriorate to a
film thickness = 150 µm marked extent if it is exposed to
moderate aggressive atmospheric
conditions for long period
ii) Wire brush to remove all loose rust and Similar to (i) but where appearance is not
scale; 2 coats drying oil type primer; 2 very important provides longer life in mild
under coats micaceous iron oxide (MXO) condition. Will provide upto 5 years life to
pigmented phenolic modified drying oil. first maintenance in polluted inland
Total dry film thickness = 170 µm
environment
iii) Blast clean the surface; 2 coats of quick Compared to (i), this would provide a
drying primer; undercoat alkyd type paint; longer life in mild conditions and could be
1 finishing coat alkyd type. Total dry film used in less mild situation e.g. inland
thickness : 130 – 150 µm
polluted, where maintenance could easily
be carried out at regular intervals
iv) Blast clean the surface; 2 coats of Suitable for general structural steel work
drying type oil primer; 1 undercoat
exposed to ordinary polluted inland
micaceous iron oxide pigmented drying environments where appearance is not
oil type paint. Total dry film
of primary importance
thickness : 165–190 µm
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