Reference
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NR/L3/CIV/140/173C
2
6th June 2009
5th December 2009
MODEL CLAUSES FOR CIVIL ENGINEERING WORKS
SECTION 173
PROTECTIVE COATING OF EXISTING STRUCTURAL STEELWORK
AND IRONWORK
Contents
Page
173.001
173.002
173.003
173.004
173.005
173.006
173.007
173.008
173.009
173.010
173.011
Coating works
Preparation of surfaces generally
Blast cleaning
Ultra High Pressure (UHP) water blasting
Power and manually operated tools
Surface preparation of weathered galvanized coatings
Application of blast Primer
Interfaces with existing coatings
Preparation of existing coatings prior to overcoating
Metal defects
Deterioration between preparing and coating surfaces
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References
British Standards
Network Rail standards
Model Clauses
7
7
7
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SECTION 173
Coating works
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PROTECTIVE COATING OF EXISTING STRUCTURAL
STEELWORK AND IRONWORK
173.001 The protective coating system(s), coatings, sealants etc., shall
be in accordance with Appendix 173/1.
Areas to receive partial protective coating systems shall be as
specified on the Contract Drawings.
Preparation of
surfaces
generally
173.002 The preparation of the surfaces of existing structural steelwork
and ironwork shall be in accordance with Appendix 173/1 and
with the relevant Clauses of this Section of Model Clauses.
Blast cleaning
173.003 Prior to blast cleaning, heavy corrosion products shall be
removed and thick deposits of oil, grease and other
contaminants shall be scraped off from the areas to be coated.
The surfaces shall then be washed down with fresh water and,
where required, an emulsifyable degreaser to remove dirt and
surface contamination using a water pressure of about 2000 to
4000 psi (140 to 280 bars).
The minimum surface standard shall be either;
i)
Sa2½ to BS EN ISO 8501-1, or
ii)
where a thermally sprayed metal coating is to be applied,
Sa3 to BS EN ISO 8501-1.
Unless otherwise agreed with the Employer’s Representative,
containment shall be provided to on-site works so that spent grit,
other debris and any overspray from the coating works does not
contaminate the ground, adjacent buildings or water, or affect
personnel or vehicles outside the work boundary.
Unless otherwise agreed with the Employer’s Representative,
non-metallic grit abrasives shall be used unless local blast
cleaning by vacuum-blasting is employed.
Except where flash blasting cleaning is used and unless
otherwise agreed with the Employer’s Representative, only grit
abrasives complying with the requirements of BS EN ISO 8504-2
shall be used. The abrasive shall be capable of providing a
sharp, angular blast profile of 70 to 100 microns amplitude (that
is, a mean peak to valley height (Rtm) of 70 to 100 microns).
Flash blast cleaning shall be undertaken using a fine
expendable abrasive, such as furnace slag or mineral abrasives,
and a pressure no greater than 2.7 bars (40 psi) to give a
surface profile of 20 to 30 microns.
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Following blast cleaning, residual dust and debris shall be
removed from blast cleaned areas using a soft dusting brush, or
a vacuum cleaner, or clean dry compressed air or a combination
of these. The level of residual dust shall be assessed in
accordance with BS EN ISO 8502-3, residual dust levels shall
not be worse than Class 1.
Arrangements for leaving in place any tightly adhering scale that
is exposed following the blast cleaning of existing coatings, shall
be agreed with the Employer’s Representative.
Ultra High
Pressure (UHP)
water blasting
173.004 The Employer’s Representative shall agree the quality of the
fresh water to be used for UHP water blasting.
All deteriorated existing coatings and corrosion products shall be
removed by the use of UHP water blasting at pressures of
between 36,000 and 40,000 psi (about 2,700 bars) and with a
water flow of between 12 and 20 litres per minute. This shall be
by use of a hand held safety lance with a rotary head, or UHP
blasting equipment fitted with a vacuum shroud. Hand held
safety lances shall be used on complicated structures which
have little flat surface area. Care shall be taken not to damage
sound coatings on surfaces adjacent to the area being treated
by UHP water blasting.
The Employer’s Representative shall determine if the level of
light flash rusting is acceptable and tightly adherent (that is, not
easily removed by wiping with a cloth). The level of flash rusting
will be compared with the pictorial reference in BS EN ISO 85014 and agreement reached following consultation with the
Contractor. Unless otherwise agreed with the Employer’s
representative, flash rusting shall be removed by dry flash
blasting.
Unless otherwise agreed with the Employer’s representative,
where no blast profile is present following UHP water blasting,
the surfaces to be coated shall be blast cleaned.
During and following UHP operations, residual water shall be
removed from all areas; water that does not drain naturally shall
be physically removed by suction, mopping or similar means.
Water discharged into the foul water sewer or surface water
drainage shall be of a quality acceptable to the Environment
Agency or local Water Authority as appropriate. This might
involve filtering out solids and possibly holding filtered water in
tanks until the results of water quality testing are available and
consent obtained for discharging the water.
When UHP is the only preparation method used, the edges of
sound coating adjacent to the prepared steel area shall be
thoroughly abraded for a minimum width of 50 mm and the
edges feathered or tapered to provide a smooth transition from
the new coating to the existing sound coating.
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Power and
manually
operated tools
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5th December 2009
173.005 Unless otherwise instructed in Appendix 173/1 or approved by
the Employer’s Representative, the use of power tools and hand
cleaning to prepare a surface ready for coating shall be
restricted to the repair of local areas and small defects.
Where power and manually operated tools are used, the areas
of exposed bare steel shall be prepared to a minimum surface
standard of St3 to BS EN ISO 8501-1 with ‘bright’ steel the
required finish. ‘Bright’ steel can be defined as ‘surfaces free
from defects with an overall bright appearance’.
Following preparation by power and manually operated tools, all
residual dust shall be removed using a soft dusting brush just
prior to the application the coating system. Following this the
surface shall be washed down with fresh water and then allowed
to dry completely: particular consideration shall be given to the
location of potential corrosion traps, crevices and recesses.
The initial Primer coat shall be applied within 4 hours of the
completion of the surface preparation.
Surface
preparation of
weathered
galvanized
coatings
173.006 Galvanized surfaces that are contaminated with any type of salt
shall be washed with fresh water by water jetting at 140 bars
(2000 psi): following this the surface shall be allowed to dry
thoroughly prior to any further preparation and coating works.
The preferred method of surface preparation is light abrasion by
flash blast-cleaning. Flash blast cleaning, which may also be
referred to as sweep blast-cleaning, is a technique used to
roughen a surface without damaging it unduly or removing the
zinc coating. Chilled iron grit shall not be used.
Previously coated galvanized surfaces shall be prepared by
lightly abrading soundly adhering paint with a medium grade
non-metallic scouring pad. Loosely adherent paint shall be
removed by scraping back to a bare zinc surface and preparing
such areas as above.
Galvanized surfaces which have weathered for more than
12 months and exhibit a dull grey surface shall have all surface
contamination deposits removed by white spirit and the surface
lightly scuffed with a medium grade non-metallic scouring pad.
The light scuffing shall be applied to produce a freshly cleaned
surface but not be so excessive as to remove the protective
dull grey film of weathered zinc.
The final preparation shall involve the washing down of the
surface with fresh water and then allowing it to dry completely:
particular consideration shall be given to the location of
potential corrosion traps, crevices and recesses.
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Application of
blast Primer
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173.007 Before applying the blast Primer, residual dust and debris shall
be removed from the blast-cleaned areas using a soft dusting
brush, or a vacuum cleaner, or clean dry compressed air, or a
combination of these. The level of residual dust shall be
assessed in accordance with BS EN ISO 8502-3, and residual
dust levels shall not be worse than Class 1.
Unless otherwise agreed with the Employer’s Representative,
the initial coat of blast Primer shall be applied to blast-cleaned
steel before the prepared surface shows any deterioration and in
all cases within 4 hours of the completion of the blast cleaning.
Where flash blast cleaning is undertaken, the initial coat shall be
applied within 1 hour of the completion of the blast cleaning.
The Primer shall be applied by an airless spray process to give a
complete obscuring coat at the specified dry film thickness.
The blast Primer shall be protected from moisture and
atmospheric contamination until the application of the next coat
of the protective coating system has been completed.
Interfaces with
173.008 Where corroded areas have been cleaned to bare metal or
where coatings of substantial thickness has been removed from
existing coatings
within an area of sound coating the edges of the surrounding
coating shall be feathered back and thoroughly abraded for a
minimum of 50 mm back from any repair area and edges shall
be feathered or tapered into the repair area to ensure a smooth
transition from the repair to sound coating.
Where 90% of a panel or other clearly defined area has been
cleaned down to bare metal, the coatings in the remaining 10%
of the area shall be removed.
A smooth transition shall be provided at the junction at overlaps,
interfaces and areas between new and retained existing
coatings.
Preparation of
sound coatings
prior to
overcoating
173.009 Soundly adhering coatings to be overcoated shall be prepared,
following the removal of any deposits of oil, grease and other
contaminants, by lightly abrading with a medium grade nonmetallic scouring pad and warm water, followed by a cold water
rinse and allowed to dry thoroughly.
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Metal defects
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173.010 Any weld spatter, rough weld caps, sharp edges, laminations or
other metal defects exposed after preparation shall be
removed. The requirements of BS EN ISO 8501-3 shall be
complied with when applicable.
Coatings around corrosion sores shall be removed from the
area surrounding each sore to exhibit at least 25 mm of ‘bright
steel’.
Except for narrow breaks in the paint film, where corrosion
sores are separated by less than 150 mm the intervening
coatings shall be removed.
Pitting shall be opened out unless this is likely to reduce the
thickness of the steelwork to below an acceptable minimum. In
such cases, the Employer’s Representative shall be consulted
to agree the acceptable minimum thickness.
Adherent mill scale shall be removed using, where necessary,
dry abrasive blast cleaning or pneumatic tools. Evidence of
significant corrosion shall be reported to the Employer’s
Representative immediately.
Evidence of significant corrosion shall be reported immediately
to the Employer’s Representative.
Following the removal of metal defects, the treated areas shall
be blast cleaned.
Deterioration
between
preparing and
coating surfaces
173.011 The surface conditions of the steelwork shall not deteriorate
between the preparation of the surface and the application of the
coatings.
When prepared or partly coated steelwork is stored uncovered at
a location classified as coastal or marine for longer than one
month, or if subject to sea mist or spray, the entire surface area
of the steelwork shall be rinsed with clean warm water and
allowed to completely dry prior to any further coating.
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5th December 2009
REFERENCES
This is a list of publications referred to within this Section of the Model Clauses. Amendments
and additions to these are provided in Appendix 173/2.
British Standards
Title
BS EN ISO 8501-1
Preparation of steel substrates before application of
paints and related products. Visual assessment of
surface cleanliness. Rust grades and preparation
grades of uncoated steel substrates and of steel
substrates after overall removal of previous
coatings.
Preparation of steel substrates before application of
paints and related products. Visual assessment of
surface cleanliness. Preparation grades of welds,
edges and other areas with surface imperfections.
Preparation of steel substrates before application of
paints and related products. Visual assessment of
surface cleanliness. Initial surface conditions,
preparation grades and flash rust grades in
connection with high-pressure water jetting.
Preparation of steel substrates before application of
paints and related products. Tests for the
assessment of surface cleanliness. Assessment of
dust on steel surfaces prepared for painting
(pressure-sensitive cleaned steel tape method).
Preparation of steel substrates before application of
paints and related products. Surface preparation
methods. Part 2: Abrasion blast-cleaning.
BS EN ISO 8501-3
BS EN ISO 8501-4
BS EN ISO 8502-3
BS EN ISO 8504-2
Network Rail standards
Title
NR/L3/CIV/040
Specification for the use of protective coating
systems
Model Clauses
Title
176
Protective coating systems
Issue date
2007
2007
2006
2000
2000
Issue date
03/09
Issue date
06/09
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