Coating Repair Specifications
Contents
1.0
Definitions
2.0
Precautions
3.0
Recommended Tools & Consumables
4.0
Intercoat Coating Repair
5.0
Topcoat Coating Repair
1.0
Definitions:
1.
Holiday: Flaw
or defect in the coating that exposes or could expose the
underlying substrate.
2.
Stress Riser: Area of the coating, which protrudes
abruptly above the contiguous area coating level. Typically found at coating interfaces, substrate edge
interfaces or large, coating filled, substrate pitted areas.
3.
Recoat Window: Time interval during which a
subsequent coat of a multi-coat system can be applied.
Associated terms include minimum and maximum recoat time.
4.
Minimum Recoat Time: Time required for a coat to
become sufficiently cured to resist thickness disturbance when
overcoated or lightly abraded with fine-medium grit paper to
remove unevenness or to repair defects.
A general guideline determines minimum recoat time to be
10% of full cure per coating product cure schedule.
Minimum recoat is verified by Thumb Twist Test.
5.
Maximum Recoat Time: Maximum time allowed for
satisfactory intercoat adhesion without special treatment of the
surface of the prior coat. Also
the minimum cure time required before heavy abrasion of coat, i.e.
mechanical sanding with medium-coarse sandpaper or use of rotary
grinder or light ‘sweep’ abrasive blast. A general guideline
determines minimum recoat time to be 20% of full cure per coating
product cure schedule. Maximum
recoat is verified by Thumbnail Test.
6.
Thumb Twist Test: The test used to determine that an
epoxy has cured sufficiently to accept application of another coat
or for light sanding with medium grit paper to remove unevenness
or repair defects. The
thumb is pressed into the coating with moderate pressure and
twisted simultaneously. If
there is no visible disturbance of the epoxy and there is no epoxy
on the thumb, the coating is sufficiently cured to accept another
coat or for light sanding.
7.
Thumbnail Test: The test used to determine whether
or not the coating recoat window has closed.
The thumbnail is pressed into the epoxy with enough force
to deflect the nail. If
no evidence of an impression remains when the thumbnail is
removed, the recoat window has closed.
8.
Tie-in Zone: The feathered zone between fresh and
existing coating.
9.
Feather: Creating
an abraded tapered transition along interfaces between coating
materials or between coating and bare substrate. Feathered edges promote interface adhesion without the stress
riser and unsightly condition that would otherwise occur at abrupt
edges.
10.
Mask: To
prevent inadvertent overlap onto surfaces that are not intended or are unsuitable for overcoating.
2.0 Precautions:
1.
Preening tools may damage some surfaces or change material
properties.
2.
Coatings that have exceeded allowable shelf life must not
be used.
3.
Coating material and cleaning solvent fumes and other
materials associated with this process may
be toxic. Safety
measures specified on MSDS must be followed.
4.
Organic fumes associated with coating material fumes in
areas serviced by HVAC charcoal filters may affect filtration
systems.
5.
Unused portions of coatings may be considered hazardous and must be mixed, hardened, and
disposed of in accordance with customers chemical control
procedures.
6.
To avoid improper mix ratios, do not mix partial epoxy kits unless mass and/or volume ratios have
been verified using mass/volume ratios as provided in coating Data
Sheet.
7.
Ensure that use of chemicals is allowed for the work area.
3.0 Recommended Tools and
Consumables:
1.
Sandpaper
2.
Scraper
3.
Non-woven abrasive pad such as Scotchbrite.
4.
Wire brush.
5.
Rotary wire brush, wheel or cup
6.
Disc sander
7.
Non-woven abrasive disc, wheel or cup
8.
Flapper wheel
9.
Abrasive blast equipment using water and oil free
compressed air for larger sweep areas.
10.
Pistol blaster for spot blast.
11.
Chloride free abrasives;
·
12/40-20/40
Black Beauty;
·
25-40
mesh Steel Grit;
·
24-36
mesh Aluminum Oxide;
·
16/35-8/20
Mesh Silica Sand.
12.
Quality Control equipment to monitor air and surface
temperature, humidity control equipment, dust collection equipment
as required to maintain specified environmental conditions and
ensure proper air flow.
13.
Cleaning solvent MEK (methylethylketone) or Isopropyl
Alcohol in solvent controlled areas.
4.0 Intercoat Coating
Repair:
4.1
Between coats: Visually inspect coating for obvious defects
and stress risers prior to application of subsequent coating.
4.2
If a minor coating defect is identified record the
observation on the ARCOR® Daily Procedure Log.
<HOLD
POINT>
4.3
Determine whether Minimum Recoat Window has passed using
Thumb Twist Test.
4.4
Determine whether Maximum Recoat Window has passed using
Thumbnail Test.
4.5
WHEN
coating has passed minimum recoat time AND
has not passed maximum recoat time, touch-up and repair can
commence.
4.6
IF
coating repair can be completed before the maximum recoat window
is exceeded then apply touch-up coating and blend ridges and/or
lumps and level the surface.
<CAUTION>
In order for the above test to be valid the touch-up repair must
proceed in the same direction as the coating was/is applied i.e.
the first areas the coating is applied would be the first areas
tested and repaired.
4.7
If local surface areas protrude above surrounding coating
material e.g. runs or a stress riser, or if debris or foreign
matter is observed in the coating the area must be abraded to
level the surface.
4.8
Using medium grit sandpaper or an abrasive pad abrade the
coating in a linear fashion i.e. left to right or up and down.
4.9
WHEN
abrading is complete, using a combination of brushing, vacuuming
and solvent wipe, REMOVE all
dust and debris from the surface.
4.10
If after abrading the abraded area is determined to be
lower than the surrounding coating, as in removal of debris, apply
touch-up material and level the surface.
5.0 Topcoat Coating Repair
5.1
Visually inspect coating for obvious defects and stress.
5.2
If a minor coating defect is identified record the
observation on the ARCOR™ Daily Procedure Log.
<HOLD
POINT>
5.3
Determine whether Minimum Recoat Window has passed using
Thumb Twist Test.
5.4
Determine whether Maximum Recoat Window has passed using
Thumbnail Test.
5.5
WHEN
coating has passed minimum recoat time AND
has not passed maximum recoat time, touch-up and repair can
commence.
5.6
IF
coating repair can be completed before the maximum recoat window
is exceeded then apply touch-up coating and blend ridges and/or
lumps and level the surface.
<CAUTION>
In order for the above test to be valid the touch-up repair must
proceed in the same direction as the coating was/is applied i.e.
the first areas the coating is applied would be the first areas
tested and repaired.
5.7
If local surface areas protrude above surrounding coating
material e.g. runs or a stress riser, or if debris or foreign
matter is observed in the coating the area must be abraded to
level the surface.
5.8
Using medium grit sandpaper or an abrasive pad abrade the
coating in a linear fashion i.e. left to right or up and down.
5.9
WHEN
abrading is complete, using a combination of brushing, vacuuming
and solvent wipe, REMOVE all
dust and debris from the surface.
5.10
If after abrading the abraded area is determined to be
lower than the surrounding coating, as in removal of debris, apply
touch-up material and level the surface.
5.11
IF
coating repair cannot
be completed before the maximum recoat window is exceeded then it
is advisable to wait until maximum recoat has passed. Heat may be
applied to accelerate cure. Consult the material Data Sheet and
Cure Schedule for direction.
5.12
Once the maximum recoat window has passed Use a High
Voltage Spark Test to locate pinholes/defects. Consult ARCORâ
‘General Specification’ Section 6.6 for Spark Test procedures.
5.13
If a defect is identified circle the area with a chalk and
record the observation on the ARCORâ
Daily Procedure Log.
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