Painting Technical Help

Bleeding

Condition : Original finish discolouring or colour seeping through the new topcoat colour.

Causes
            »     Contamination - usually in the form of soluble dyes or pigments on the older finish before it
                                                was repainted. (This is especially true with the older shades of red)
Prevention
            »      Thoroughly clean areas to be painted before sanding, especially when applying lighter over
                    darker colours

Solution:    Apply two medium coats of Bleeder seal in accordance with label instructions. Then reapply colour coat.

Blistering

Condition: Bubbles or pimples appearing in the topcoat film, often months after application

Causes
            » Improper surface cleaning or preparation
Tiny specks of dirt are left on the surface can act as a sponge and hold moisture. When the finish is exposed to the sun ( or abrupt changes in atmospheric pressure), moisture expands and builds up pressure. If the pressure is great enough, blisters form.

            » Wrong thinner or reducer
Use of a fast dry thinner or reducer, especially when the material is sprayed too dry or at an excessive pressure. Air moisture can be trapped in the film.

            » Execessive film thinkness
Insufficient drying time between coats or too heavy application of the undercoats may trap solvents which escape later and blister the colour coat.

            » Contamination of compressed air lines
Oil, water or dirt in lines.

Preventation
            » Thoroughly clean areas to be painted before sanding. Be sure surface is completely dry before
                applyiong either undercoats or topcoats. Don't touch a cleaned area as the oild in your hands will
                contaminate the surface.
            » Select the thinner or reducer most suitable for the existing painting environment conditions.
            » Allow proper drying time for undercoats and topcoats. Be sure to let each coat flash before
                applying the next.
            » Drain and clean air pressure regulator daily to remove trapped moisture and dirt. Air compressor
                tank should also be drained daily.

Solution: If damage is extensive and severe, paint must be removed down to undercoat or metal, depending on the depth of blisters. Then refinish. In less severe cases, blisters may be sanded out, resurfaced and re-topcoated.

Blushing

Condition: Milky white haze that appears on laquer films.

Causes
            » In hot humid weather, moisture droplets become trapped in teh wet paint film. Air curremts from
               the spray gun and the evaporation of the thinner tend to make the surface being sprayed lower in
               temperature than the surrounding atmosphere. This causes moisture in the air to condense on the
               wet paint film.
            » Excessive air pressure
            » Too fast a thinner

Prevention
            » In hot humid weather try to schedule painting early in the morning when temperatures and
               humidity conditions are more suitable, use acrylic lacquer thinner.
            » Use proper gun adjustments and techniques.
            » Select the thinner that is suitable for existing painting environment conditions.

Solution: Add retarder to the thinned colour and apply additional coats.

Chalking

Condition : Formation on the finish casued by pigment powder no longer held by the binder, which makes
the finish look dull.

Causes (other than normal exposure)
            »Wrong thinner or reducer, which can harm topcoat durability
            » Materials not uniformly mixed.
            » Starved paint film
            » Excessive mist coats when finishing a metallic colour application.

Prevention
            » Select the thinner or reducer that is best suited for existing environmental conditions
            » Stir all pigmented undercoats and topcoats throughly
            » Meet or slightly exceeed minimum film thickness.
            » Apply metallic colour as evenly as possible so that misting is not required. When mist coats are
                necessary to even out flake, avoid using straight reducer.

Solution: Remover surface in affected area by sanding. Then clean and refinish.

Chemical Staining

Condition: Spotty discolouration of the surface.

Causes
            » Atmospheric contamination falling on the finish in the presence of moisture or rain- usually due to
                adjacent industrial activity
Prevention
            » Avoid contaminated atmosphere or wash surface with detergent and water as soon as possible
                after exposure.
            » Apply clear coat.

Solution: After washing with detergent and water, rub affected area with rubbing compound and polish. in severe ases, sand to prime and refinish

Chipping

Condition: Small chips of a finish losing adhesion to the underlying layer (Substrate) usually caused by impact of stones or hard object.

Cracking (line Checking, Micro- Checking)

Condition: A series of deep cracks resembling mud cracks in a dry pond and in no definite pattern, they are usually through the colour coat and sometimes the undercoat as well.

Causes
            » Excessive film thickness. (Excessively thick topcoats magnify normal stresses and strains which
                which can result in cracking even under normal conditions)
            » Materials not uniformly mixed
            » Insufficient flash time
            » Incorrect use of additive

Prevention
            » Don't pile on topcoats. Allow sufficient flash and dry time between coats. Do not dry by gun
               fanning
            » Stir all pigmented undercoats and topcoats thoroughly. Strain and where necessary, add fish Eye
                Eliminator to topcoats.
            » Read and carefully follow label instructions. (Additives not specially designed for a colour coat
               may weaken the final paint film and make it sensitive to cracking)

Solution: The affected areas must be sanded to a smooth finish or in extreme cases removed down to the bare metal and refinished.

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