Specifying Repaint Work with MPI’s
DSD System
Content adapted from MPI’s Level 2 Maintenance Repainting Coatings
Specialist course
Identifying defects and failures in the coating and the substrate to be
painted is the first step in maintenance repainting work; this helps determine
the best course of action with regard to required repairs (if any), surface
preparation, level and type of priming, and selection of the new coating
system.
MPI identifies five “Degrees of Surface
Degradation” that quantify how badly
the substrate or coating
hasdeteriorated and thus determine
how rigorous the surface preparation or
primingwork will need to be:
DSD-0 (pictured here): This is
anessentially "sound" surface or previous coating where there is no
damage to the surface, and painting work is being done to provide a
change in color, sheen, etc. Any visual (aesthetic) defects do not affect
the film’s protective properties. The required surface preparation will be
to assure the surface is free of contaminants and sufficiently deglossed
or roughened to assure good adhesion of the new coating.
DSD-1: This is a “slight” degree of surface degradation. It is unlikely
that the topcoat has been anything but insignificantly breached, and in
no case is the substrate exposed. Surface preparation requirements
should be “slight” and only touch-up painting with the top or
intermediate coat should be necessary.
DSD-2: This is a “moderate” degree of surface degradation. Damage to
the film integrity is such that spot priming and topcoating after
moderate surface preparation requirements should be adequate.
DSD-3: This is a “severe” degree of surface degradation. Damage to
the coating is widespread and the amount of surface preparation
required will likely be substantial, including complete removal of any
existing coatings down to the bare substrate. A full coat of the
appropriate primer and intermediate/topcoat system is to be expected.
DSD-4: This is an essentially “unsound” surface. Repainting is only a
temporary cosmetic remedy as the substrate needs to be repaired or
replaced before an appropriate coating system can be applied.
The evaluation begins by taking note of what surface defects and
contaminants are present.
Common Surface Defects*
Alligatoring. This term refers to a random
pattern of roughly parallel and
perpendicular cracks that look like the scaly
hide on the back of an alligator or crocodile.
These cracks may extend to a previous coating or may expose the original
substrate. Possible causes may be the application of:
a top coat before the undercoat is dry
a top coat unable to bond to a glossy surface
excessive coats of paint
an excessively thick coat that prevents the under coat from drying
properly
a hard, rigid coating (e.g. alkyd enamel) over a soft, flexible coating (e.g.
latex)
With oil/alkyd coatings, alligatoring can be the natural result of aging where
the film hardens, loses its elasticity, and during temperature fluctuations is
unable to expand and contract with the substrate underneath.
Blistering.This defect appears as dome-shaped
bubbles that result from localized loss of adhesion
and the consequential lifting of the film from the
underlying surface. Blistering is commonly caused
by water or moisture vapor migrating through a
painted substrate. Blistering can also be caused by
excessive heat during application that causes the
surface to dry too quickly. Blistering continuing to a bare substrate usually
indicates a moisture-originated blister, whereas heat initiated blisters often
extend only to the next solid coating. The standard for evaluating and
quantifying blistering is ASTM Method D 714"Evaluating Degree of Blistering
of Paints."
Cracking. Cracking is a breach in a dry paint film
that appears as a line or connecting lines that
extend to the substrate or coating below. The most
frequent cause is substrate movement from settling,
shrinkage expansion, moisture loss/gain, or physical
distortion. Shrinkage of the coating can also create
cracks; this occurs more with thick film applications
of high PVC (pigment volume concentration) paints.
Chalking. A loose, white powdery pigment residue on the surface of a
coating accompanied by a loss of gloss and lightening of the color. Chalking
should not be confused with efflorescence (deposition of soluble salts on a
coating's surface) or erosion (gradual wearing of the film due to
environmental conditions). The source of chalk is the coating's pigment
being released from the film. In some cases,
this is a self-cleaning feature purposely
designed into the coating. Some causes:
paint spread too thin, or thinned too much
low quality, highly pigmented paint
indoor paint used on exterior substrate
use of epoxy paint in direct sunlight
The standard for evaluating and quantifying
chalking is ASTM Method D 659.
MPI Levels of Surface Degradation for Exterior Concrete Masonry
Surfaces
Here’s how a specifier would use an evaluation of surface defects to
determine which level of surface degradation he’s dealing with:
DEFECT
DSD1
DSD2
DSD3
Alligatoring
None
Slight
Moderate to Severe
Blistering
None
Slight
Moderate to Severe
Cedar Stains
Minor Spots
Minor Spots
Moderate to Severe
Checking
None
Slight
Moderate to Severe
Cracking
None
Slight
Moderate to Severe
Dirt/Dusts
Any
Any
Any
Efflorescence
Slight
(surface)
Moderate
Heavy
Erosion/Chalking
Slight to
Moderate
Moderate
Moderate to Severe
Flaking/Peeling
(1)
Slight
Moderate
Moderate to Severe
Flaking/Peeling
(2)
None
Moderate
Moderate to Severe
Mildew
Slight to
Moderate
Moderate
Moderate to Severe
Oils/Grease
Any
Any
Any
Rust Stains
Slight
(surface)
Slight to
Moderate
Moderate to Severe
Sagging
Slight to
Moderate
slight to
Moderate
Moderate to Severe
(1) Flaking/peeling from the topcoat through some or all coats. Primer
remains intact.
(2) Flaking/peeling down to the substrate. Primer not intact.
Here’s what those surfaces might look like…
DSD-1 Slightly Deteriorated Concrete Masonry
Surface
Some surface staining and contamination on
concrete block.
DSD-2 Moderately Deteriorated
Concrete Masonry Surface
Block wall shows localized efflorescence
and peeling, flaking, mildew, and cracking.
DSD-3 Severely Deteriorated Concrete Masonry Surface
Building with severe peeling, flaking, mildew, and cracking.
DSD-4 Substrate Damage
The surface requires repairs or replacement prior to painting to achieve the
owner’s required structural, protective, or esthetic function
Once the DSD level has been determined, MPI’s Repaint Manual provides
guidance for the required surface preparation prior to coating application.
For a DSD-2 moderately deteriorated concrete/masonry surface, the
recommended surface preparation steps might look like this, with the
appropriate MPI surface preparation standard (RSP) indicated for each step:
“All surface contaminants such as wax, oils, grease, dirt, tire marks
(horizontal surfaces), etc., must be removed from the surface. Oil and
grease can be removed by detergent cleaning (MPI RSP-13), followed by a
rinse with clean water; solvent cleaning (MPI RSP-2) can be used as an
alternative to MPI RSP-13 on areas with a concentration of oil or grease. All
loose and flaking paint must be removed by hand cleaning (MPI RSP-1),
power tool cleaning (MPI RSP-4), or pressure washing (MPI RSP-5). All
blisters must be removed from the surface and the edges feathered. Areas
showing mildew growth must be treated as outlined in MPI RSP-9. Glossy
finishes must be ‘dulled’ by sanding (MPI RSP-1) or (MPI RSP-4), by a TSP
treatment (MPI RSP-13), or by sweep blasting (SSPC-SP 7) to create an
anchor pattern to promote adhesion of the new coating. Rust stains can be
removed with an oxalic acid treatment (MPI RSP-12). If large amounts of
efflorescence are present, mechanical removal (e.g. abrasive sweep blasting
or power tool grinding) may be required, after which acid etching (MPI RSP8) shall be performed. After any application of muriatic acid, the surface
must be flushed with large amounts of clean water to remove any residue,
and then allowed to dry thoroughly. The pH of the surface shall be tested, as
specified in 1.2 pH Testing before the application of paint. All bare areas
must be spot primed.”
*Excerpted from MPI's Identifiers: Defects and Failures book
Stay up-to-date on industry best practices and trends with
FREE MPI Updates