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Dacrylate Paints Ltd.

Paint Problems and Problem Solving

Paint Problems and Problem Solving

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Cissing, pin holing, crawling
Description : Holes, disruptions and depressions present in the film, usually visible directly at the application stage.
Causes : Most often caused by a contaminated substrate, residual oil or grease left on steel, grease from hands & fingers during handling, contaminated equipment (e.g. gun previously used for hammer finish), contaminated air supply (oil), airborne contamination from other processes, weld-spatter release residue, flux residue or  mould release agent residue etc.
Slow drying
Description : Retarded drying of the film or system.
Causes : Low temperatures, incorrect mixing of two packs, poor air movement, incompatible components in a multi coat system, excessive film thicknesses, reaction with underlying substrate (e.g. plasticiser migration), old paint stock (usually alkyds), incorrect thinner.
Runs, sags, curtains and tears
Description : Uneven flow pattern in a vertical paint film resulting in areas of excessive film build.
Causes : Excessive film thicknesses, incorrect thinner (too slow), over-thinning, gun to object   distance too small, gun fan size too narrow, gun fluid tip too large, air pressures too low.
Solvent boil, gassing, bubbles
Description : Small bubbles (whole or burst) in the cured film.
Causes : High temperatures, incorrect thinner (too fast), entrapped air being released from substrate (e.g. metal sprayed), liberation of CO2 during curing of two pack polyurethanes, air entrainment during spray application (air leaks).
Wrinkling
Description : A disruption of the cured film leaving an irregular wrinkled surface.
Causes : Over-coating intervals too short (swelling of underlying film), excessive film thicknesses of underlying coats, incorrect thinner, incorrect mixing of underlying two pack coats, incompatible components in a multi coat system.
Dry Spray
Description : A dry 'sandy' effect on the paint surface, usually varying in intensity.
Causes : High temperatures, incorrect thinner (too fast), under thinning, gun to object distance too great, air pressures too high, overspray from other areas landing on previously painted and partially cured film.
Reduced pot life
Description : Working life of a two pack mixture is less than expected.
Causes : Incorrect mixing (not stirred thoroughly), incorrect mixing (not measured accurately),  high temperatures, incorrect hardener used.
Cracking, flaking, peeling
Description : Splits, detachment or partial detachment of the dried coating.
Causes : Incorrect system for substrate (eg alkyds on zinc), excessive movement of substrate (eg. expansion/contraction), excessive moisture in timber (e.g. water ingress from un-painted areas) inflexible paint film, incorrect mixing of two packs, age embrittlement of coating, substrate too soft for subsequent paint film (e.g. fresh bitumen).
Bleeding
Description : Discolouration of the paint film, often patchy.
Causes : Leaching of solvent soluble pigments, dyes or coloured resins (e.g. bitumen) from the underlying substrate or previous coatings, incorrect thinner (too harsh), unsuitable system.
Poor adhesion
Description : Detachment of coating, reduced adhesion of film to substrate or between individual coatings in the system.
Causes : Contamination or poor preparation of substrate, insufficient abrasion, inadequate degreasing, poor pre-treatment (e.g. phosphating), unsuitable system on “difficult surfaces”, excessively long recoating intervals, excessive film thicknesses (etch primers).
Skinning
Description : A skin formation on the surface of the paint whilst in the container, sometimes broken up by agitation and distributed throughout the paint.
Causes : Container not tightly sealed during storage or left open for long periods during use, poor storage conditions.
Bits
Description : Inclusions within the dried film.
Causes : Poor filtration of paint prior to use (broken skins), airborne contamination from other operations or from the outside environment, poor surface preparation, dirty booth filters or floors, contaminated air supply, dirty application equipment.
Colour differences
Description : Shade differences between items painted with same material.
Causes : Varying film thicknesses (substrate “grinning through”), poor mixing of paint prior to application, contamination of equipment (poor cleaning of spray guns etc), bleeding from underlying surfaces (see bleeding).
Orange Peel
Description : Poor film flow resulting in an uneven film showing characteristic dimples resembling an orange skin’s surface.
Causes : High substrate temperatures, low paint temperature, incorrect thinner (too fast), air pressures too low, paint too thick, incorrect spray gun set-up.
Gloss differences
Description : Sheen differences between items painted with same material.
Causes : Varying film thicknesses, poor mixing of paint prior to application, contamination of equipment (poor cleaning of spray guns etc), varying temperatures during drying.
Chalking
Description : The formation of a loose white chalky deposit on the film surface during weathering, easily removed by wiping to reveal underlying original colour.
Causes : Breakdown of the film binder (usually by U.V. degradation), unsuitable binder type (e.g. epoxy) for final finish.

    

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