Aplicacion de la capa refuerzo , como y cuando aplica.

1. SSPC-PA Guide 11
August 1, 2008
1
SSPC: The Society for Protective Coatings
Paint Application Guide No. 11
Protecting Edges, Crevices, and Irregular Steel Surfaces by Stripe Coating
1. Scope
This guide discusses the technique called “stripe coating”
or “striping” as a way of providing extra corrosion protection
measures on edges, outside corners, crevices, bolt heads,
welds, and other irregular steel surfaces, including optional
surface preparation techniques for sharp edges to improve
coating performance. Some details, including the advantages
and limitations of specific methods of obtaining additional
coating thickness, are described to assist the specification
writer in assuring that the project specification will address
adequate corrosion protection.
2. Background
2.1 Sharp edges, outside corners, crevices, and welds
are often sites where coating failures and corrosion begin due
to reduced coating barrier protection (see Figure 1). Reduced
coating thickness on these surfaces can be a result of applica-
tion of inadequate amounts of coating, but the surface tension
of the wet coating or coating shrinkage during the drying/curing
process can also pull the film away from edges. Sharp edges
resulting from cutting, burning, and shearing are especially
difficult to coat adequately. Bolt threads combine the adverse
effects of sharp edges and crevices.
2.2 The solutions to this problem include (1) eliminating
the irregularities by grinding, mechanical sanding, or filing;
(2) applying a thicker protective coating film to problem areas
such as outside edges, pitted areas, and bolts; (3) applying a
penetrating and/or good wetting coating to crevice areas and/
or inside corners; or a combination of (1) and (2). In some
cases, both grinding and stripe coating may be specified for a
given area. The option of choice is usually determined by the
best cost/benefit ratio. Factors that enter into the cost/benefit
analysisofedgeprotectionincludetheseverityoftheexposure
environment,interferencewithproductionduringmaintenance,
anddifficultyinaccessingthestructuretoperformmaintenance
painting. These factors are unique to each project.
2.4 Sharp edges may be avoided at the prefabrication
stage or remedied by grinding after construction, but at a much
higher cost. When filing edges, care should be taken to assure
that additional sharp edges are not created while modifying the
original edge. It is generally much less expensive and easier
to grind or chamfer edges in the shop than in the field.
2.5 Additional coating thickness can be obtained by
applying an extra layer of coating to the areas requiring addi-
tional protection (the “stripe coat”). In some cases, the “stripe
coat” may be followed by the application of a full coat of a
coating with edge retention properties.
3. Preparing Outside Corners and Sharp
Edges
3.1 Outside corners and sharp edges can be ground such
that the edge is rounded to a 1.6 to 3.2 mm (1/16 to 1/8 inch)
radius. An alternative to rounding is to chamfer the edge to a
specified measurement, so instead of one 90-degree corner,
therearetwo135-degreecorners(seeFigure2).Thewidthofthe
flat ground area, i.e. the distance between the two 135-degree
corners, is usually 1.6 to 3.2 mm (1/16 to 1/8 inch). Paint will
not pull away from a 135-degree corner as much as from a
90-degree corner, resulting in more overall coating thickness.
Further, subsequent abrasive blast cleaning provides some
radius to the 135-degree corners.
Figure 1. Schematic showing how coating thick-
ness is reduced at a sharp edge.
90°
135 °
Chamfer
Figure 2. Chamfering reduces a sharp 90° corner to
two 135° corners.
Poor
Coating
Ideal

2. SSPC- PA Guide 11
August 1, 2008
2
3.2 The increased performance resulting from rounding
or chamfering edges depends on the service environment, the
generic type of coating and on the radius or size of the chamfer.
One research study1
showed that rounding or chamfering had
no measurable effect if an ethyl silicate inorganic zinc-rich
(IOZ) coating was applied over blast cleaned steel. Therefore,
there is no need to go to the added expense of grinding edges
if ethyl silicate IOZ coating is specified. However, the same
study indicated that rounding or chamfering edges before
application of an alkyd or organic zinc-rich primer improved
the coating’s performance. Even with edge rounding or cham-
fering, it is necessary that proper spray application techniques
be used.2,3
The use of coatings with edge-retention properties
(see Section 4.7.3) may also minimize or eliminate the need
for edge grinding.
3.3 Edge grinding is best done in the shop before blast
cleaning where the work is accessible. A sample statement
in a specification may read, “All corners and edges shall be
rounded to a 2 mm radius (1/16 inch) or ground to a 2 mm
(1/16 inch) chamfer.” In addition to edges, rough surfaces are
ground smooth. Flame cut edges are normally ground over
their entire surface to remove the hardened surface layer
resulting from flame cutting and permit creation of a profile.
For immersion service and other services where increased
corrosion can be expected, very rough welds should always
be ground because many coatings cannot adequately protect
them. NACE Standard RP0178 "Standard Recommended
Practice: Fabrication Details, Surface Finish Requirements,
and Proper Design Considerations for Tanks and Vessels to
Be Lined for Immersion Service"4
provides guidance on finish
requirements for welds.
4. Stripe Coat Application
A “stripe coat” is a coat of paint applied only to edges,
welds, outside corners, bolt heads and threads, and crevices,
either before or after a full coat is applied to the entire surface.
These areas are difficult to coat due to coating shrinkage
during cure. Shrinkage pulls coating away from sharp edges,
resulting in low dry film thickness. Wet coating may flow over
rather than into crevices. This results in a temporary creating
bridge over the crevice that disappears as the coating cures
and shrinks, leaving the crevice interior unprotected. Both
areas are susceptible to premature corrosion. The practice
of applying a “stripe coat” to such areas is frequently referred
to as “striping.”
The project specification normally specifies the areas are
to be striped, how to apply the stripe coat (brush or spray), in
what order to apply the stripe coat (before or after the full coat),
which coats are to be striped, whether tinting of the stripe coat
or use of another color of coating is required, and information
on the drying/curing requirements between application of the
stripe and full coat (may defer to the coating manufacturer).
4.1AreastoStripe:Thefacilityownernormallydetermines
whether stripe coating is warranted for some or all areas of the
particular project. Sometimes only specified areas of outside
corners, edges, welds, and crevices are striped. Situations
where stripe coating is usually warranted are:
Immersion service (e.g., interiors of fuel or water•
storage tanks; ship hulls)
Areas with high corrosion rates (e.g. cooling towers•
and splash zones)
Areas where access is difficult (e.g., towers, some•
bridges).
Built up members (e.g., lattice bars and boxes)•
Situations where stripe coating may not be cost effective
are:
Non-critical components (e.g., interior wall in living•
space on a ship)
Mild exposure (e.g., SSPC environmental exposure•
zones 1A and 1B(1),5
Inside corners (can be adequately covered using•
proper spray technique)
Areas that are usually stripe coated include:
Crevices•
Plate and sharp edges•
Plate seams•
Back-to-back angle seams (built up members)•
Pitted steel•
Bolt heads and nuts•
Rivet heads•
Welds•
Other sharp discontinuities•
Outside corners•
•
Stripe coating is most effective on edges that are either
rounded or chamfered by grinding (see Section 3).
4.2 How to Stripe
4.2.1 Brushing is the preferred method of applying stripe
coats. Unless otherwise specified, SSPC-PA 1 requires brush
application of coatings to cracks, crevices, blind areas of all
rivets and bolts, and all areas of limited access.(2),6
Brush
application provides the highest quality stripe coat on most
surfaces because it works the paint into the pores and crevices
and allows the greatest control over the boundaries of the
painted area. The coating should be allowed to dry to recoat
according to the product data sheet before the full prime coat
is applied. Coating manufacturers will usually provide guid-
ance on the amount of dry time required before application of
(1)
SSPC Environmental Zone 1A–Interior, normally dry (or tem-
porary protection). Very mild (oil base paints now last six years
or more). SSPC Environmental Zone 1B–Exterior, normally dry
(includes most areas where oil base paints now last six years or
more)4
(2)
SSPC-PA 1, Section 7.4.6.

3. SSPC-PA Guide 11
August 1, 2008
3
subsequent coatings. Table 1 compares application of stripe
coats by brush or spray.
4.2.2Whenapplyingastripecoat,thebrushstrokesshould
run parallel to, not across, edges and crevices. Variations in
pressure of the brush during application can result in thin film
on sharp edges and accumulation of coating on adjoining
perpendicularsurfaces.Toassureadequatefilmbuildonsharp
edges, multiple brush applications may be necessary. Bolt
heads and nuts should be striped in a circular brush motion.
Striping should extend at least 3 centimeters (cm) (1 inch) from
edges and other irregular surfaces. Round or oval brushes are
generally considered most suitable for rivets, bolts, irregular
surfaces, and rough or pitted steel.
4.2.3 SSPC-PA 1 does not permit rollers to be used to
applycoatingsonirregularsurfaces,suchasrivets,boltheads,
crevices, welds, corners or edges unless otherwise specified.
(3)
If the project specification permits the use of rollers for stripe
coat application in these areas, PA 1 requires that the coating
be brushed out to form a continuous and unbroken film over
these surfaces.
4.2.4 Spraying the stripe coat can reduce the amount
of time spent in brush application, but the painter has less
control over the precise boundaries of the area being coated.
Spray may be the best method for applying stripe coats using
coatings with edge retention properties or zinc-rich coatings,
or for applying a stripe coat to edges that have already been
painted. The applicator should spray the coating along the flat
surface, not directly at the edge itself, to prevent the atomiza-
tion pressure from pushing the coating away from the edge
that is to be protected.
3 SSPC-PA 1, Section 7.3.4.
4.2.5 When striping with a coating that is prone to pigment
settling, such as zinc-rich primers, the coating in the pot should
be constantly agitated, unless otherwise recommended by the
coating manufacturer.
4.2.6Whenstripingwithamulti-componentthermosetting
coating, the curing reaction will eventually progress to the point
where the coating fails to wet the surface and level adequately.
Sincehightemperaturesoftenacceleratecuringrates,thiseffect
ismostpronouncedinhotweather.Heatofreaction(exotherm)
may also be generated when multiple components of thermo-
setting coatings are mixed, so it may be more cost effective
to use smaller kits (e.g., 1-liter or 1-gallon units) rather than
5-liter or 5-gallon units. Note that most coating manufacturers
prohibit mixing of partial kits. Thinning should not be used to
restore the flow properties of a multi-component coating that
has increased viscosity from partial curing.
4.2.7 It is good practice for the stripe coat to be a different
color from the adjoining full coats or the bare steel surface.
Thecolordifferenceenablespaintersandinspectorstovisually
verify there are no misses, skips, or thin spots in the stripe coat.
In addition, the application can be verified after the fact (as
necessary) for thickness and proper coverage using a destruc-
tive thickness gage (i.e., Tooke Gage), a holiday detector, or
(on some specialty coatings) ultraviolet light.
4.3 What Coats to Stripe: Usually, a stripe application is
specified for the primer coating because of the importance of
complete coverage. After a surface has received its first coat
of paint, there is less probability of incomplete coverage of
subsequent coats. Occasionally, multiple stripe coats may be
required over rough hand welds. In critical areas, the specifier
TABLE 1
COMPARISON OF APPLICATION METHODS
APPLICATION
METHOD
ADVANTAGES DISADVANTAGES
Brush Best method to work paint into pores and•
crevices
Most complete coverage of rivet heads, bolt•
heads, nuts, and threads
Best control of extent of area coated•
Most labor-intensive method•
May pull incompletely cured paint from edge•
Spray Fastest method of application•
Least labor-intensive method•
May be best method of applying coatings with•
edge retention properties, zinc-rich coatings
Quick method for applying a stripe coat to•
edges al-ready painted
May bridge (rather than penetrate into) pores and crev-•
ices. Back-brushing needed to work wet coating into
pits, crevices, and angles.
More likely to miss areas in tight spaces, resulting in•
holidays.
Builds coating thickness on larger area (control of area•
coated is difficult)
More risk of overspray and dry spray•

4. SSPC- PA Guide 11
August 1, 2008
4
may require that striping be done for two or more coats in a
multi-coat system. Nevertheless, multiple coat striping is not
commonly specified.
4.4 When to Stripe - Before or After Full Coat
4.4.1 Many coatings professionals feel that the stripe
coat of the primer should be applied first to maximize corro-
sion protection. For example, it is easier to work stripe coats
into crevices that have not been bridged by a spray-applied
full coat. However, there are several reasons why the stripe
coat could be applied after the first full coat. If the stripe coat
is applied prior to primer application, there is opportunity for
the surrounding clean, unprotected steel to deteriorate while
the stripe coat is drying/curing. Another reason is that stripe
coating after application of the full coat (particularly an inter-
mediate coat) will fill in pinholes and other holidays that have
formed in the spray-applied coat.
4.4.2 If striping is specified for each coat in a multi-coat
system, application of the stripe coat before the final finish
coat will result in a more uniform finish.
4.4.3 When painting a tank floor or other surface subject
to foot or vehicle traffic, it may be wise to delay application of
the final stripe coat over the welds to minimize erosion of the
coating by foot traffic or air hoses being dragged across the
raised welds prior to the coating being put into service.
4.4.4 The advantages and limitations of striping before
and after the full coat are summarized in Table 2. Final deter-
mination of the best sequence of stripe coats and full coats will
depend on the coating systems being used and the specific
requirements of each project.
4.5 If the stripe coat is applied first, it is usually allowed to
dry to touch (per ASTM D 1640) before the full coat is applied.
However,therecanbeexceptionstothispractice.Therecoating
instructions in the coating manufacturer’s product data sheet
should be followed unless otherwise specified.
4.6 Controlling Thickness
4.6.1 The thickness of the stripe coat is difficult to control.
Somecontractorswillmeasurethicknesstoassuretheminimum
and maximum specified thickness limits have been satisfied,
while others will make only a visual check for excessive build.
For the most part, thickness is controlled by the skill of the
applicatoranduseofawetfilmthickness(WFT)gage.However,
notch gages cannot provide reliable WFTreadings on irregular
surfaces and should not be used on edges.
4.6.2 Leeway on maximum thickness is usually allowed
within 2 inches (5 cm) of an edge or 1 inch (3 cm) of a weld.
Coatings may be tolerant of thickness beyond the specified
upper limit. Near a striped area (2 inches [5 cm] from an edge
and 1 inch [3 cm] from a weld), the maximum thickness is
sometimesallowedtobetwicethenormalmaximum.Designers
orspecifiersshouldusecoatingmanufacturer’srecommended
dry film thickness (DFT) ranges as guidance for required thick-
ness of a stripe coat.
4.6.3Conflictscanbeavoidedifthicknessrequirementsat
or near the stripe coat and any allowed deviation from speci-
fied minimum and maximum DFT thickness requirements are
clearly stated in the project specification.
4.6.4 Although thickness of the stripe coat can often be
measured in the immediate vicinity of an edge, it is very difficult
to measure thickness of a coating over the edge itself. Some
TABLE 2
ADVANTAGES AND LIMITATIONS OF STRIPING
BEFORE VS. AFTER APPLICATION OF FULL COAT
TIMING ADVANTAGES LIMITATIONS
BEFORE Better application and protection of irregularities•
Better appearance•
Holidays, light spots are more obvious•
Assists painter in monitoring progress•
Rust-back of cleaned areas surrounding•
the striped area may occur before full coat
can be applied
AFTER Surroundingblastcleanedsurfacewillnotrustwhile•
stripe coat dries
Can sometimes apply by spray (brush-back usually•
required)
Better coverage of pinholes and holidays•
Can visually ensure that stripe coat has been•
applied properly
Damage to previously coated surfaces•
may occur during application of stripe
coat
Higher chance of incomplete coverage of•
irregularities
Aesthetics (stripe coat may be more•
visible)

5. SSPC-PA Guide 11
August 1, 2008
5
electronic gages include very small tips (probes) to improve
the reliability of dry film thickness readings taken on an edge.
Notches in the probe tip aid in alignment of the gauge and thin
flexible shims can be used to verify the accuracy of the gauge
when measuring on an edge.
4.7 Coatings to Use for Striping
4.7.1 Welds and crevices are best protected when striped
with a coating with good wetting properties. High build coat-
ings are best for striping edges. However, it is impractical
to specify two different stripe coatings on a job with edges,
crevices and welds. The paint should be of a consistency to
function on both surfaces.
4.7.2 The manufacturer should be consulted to determine
the appropriate coating to use for the striping. If the stripe coat
contains a zinc loading and is to be applied over a surface
already primed with inorganic zinc, an organic zinc primer
is used for the stripe coat, as inorganic zinc coatings do not
bond well over themselves or over organic zinc. High solids
coatings may have a relatively short dry time and may not
possess good wetting properties, which is paramount to the
success of the stripe coat. In this case, a compatible stripe coat
with a slower drying time and improved wetting may be used
with the high-solids coating. The coating selected for striping
should be designed for the service environment.
4.7.3 Coatings with Edge Retention Properties: An
alternative method for the protection of edges that may avoid
the need for grinding and chamfering is the use of a coating
that has edge retention properties. Typically these types of
coatings are high-solids products that provide improved film
thicknessretentionattheapexofanedgetoimproveprotection
inthesecriticalareas.Amethodformeasuringtheedgeretention
properties of a coating is published in MIL-PRF-23236C.7
This
test method compares the film thickness of three specimens
cut from a sample of coating applied to a non-chamfered 90
degree angle. The ratio of the film thickness at the apex vs. the
film thickness on the flat area is calculated and expressed as
the percentage of edge retention of the coating, as shown in
Figure3.AccordingtoMIL-PRF-23236C,anyspecimenhaving
less than 50 percent edge retention fails the test. An average
value of 70 percent edge retention for three test specimens
measured using an optical microscope is required to qualify
a coating as having edge-retention properties.
Note that very sharp edges, or “knife” edges, are very
difficult to protect even with coatings with edge-retention
properties. It is recommended that “knife” edges have their
surface modified as described in Section 3 prior to coating to
provide suitable corrosion protection.
5. Disclaimer
5.1 This guide is designed to describe, review, or analyze
new or improved technology and does not meet the definition
of a standard as defined by SSPC. A guide differs from a stan-
dard in that it is not suitable for referencing in a specification or
procurement document. SSPC guides are intended to provide
consensus recommendations for best industry practice. They
are not written as requirements that may be cited in a contract.
However,specifiersmayincorporateinformationfromanSSPC
guide into job-specific contract requirements.
5.2 While every precaution is taken to ensure that all
informationfurnishedinSSPCguidesisasaccurate,complete,
and useful as possible, SSPC cannot assume responsibility
nor incur any obligation resulting from the use of any materials,
coatings, or methods described herein, or of the guide itself.
5.3 This guide does not attempt to address problems
concerning safety associated with its use. The user of this
specification, as well as the user of all products or practices
described herein, is responsible for instituting appropriate
health and safety practices and for ensuring compliance with
all governmental regulations.
References
1. Corbett, W. D. “The Same Old Grind...An Investigation
ofZinc-RichPrimerPerformanceOverSteelCorners.”Modern
Steel Construction, Vol. 40, No. 6: p. 43-49.
2. Graco Publications, Airless Spray Techniques. Minne-
apolis, MN: Graco Inc., 1993. This document is available as a
downloadable .pdf file from http://www.graco.com.
3.GracoPublications,AirSprayTechniques.Minneapolis,
MN: Graco Inc., 1995. This document is available as a down-
loadable .pdf file from http://www.graco.com.
4. NACE Standard RP0178 (latest edition); Standard
Recommended Practice: Fabrication Details, Surface Finish
Requirements, and Proper Design Considerations for Tanks
and Vessels to Be Lined for Immersion Service.”
Measure paint thickness
here (dft )
Measure paint thickness here (dft )
PAIN
T
PAIN
T
SU
BSTR
ATE
flat
Measure paint thickness
here (dft )flat
edge
Figure 3. Diagram of edge retention test
(courtesy of MIL-PRF-23236C)
The edge retention percentage is calculated as:
% Retention = dft (edge)/dft (flat) x 100

6. SSPC- PA Guide 11
August 1, 2008
6
5. SSPC, “How to Use SSPC Standards and Guides.”
Pittsburgh,PA:SSPC,2008.Houston,TX:NACEInternational.
This standard is available from NACE International at http://
www.nace.org.
6. SSPC-PA 1 (latest edition), Shop, Field, and Mainte-
nance Painting of Steel. Pittsburgh, PA: SSPC.This standard
is available online at http:// www.sspc.org.
7. MIL-PRF-23236C (latest edition); Coating System for
ShipStructures.WashingtonNavyYard,DC:NavalSeaSystems
Command. This standard is available online at http://assist.
daps.dla.mil/quicksearch