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Paint Defects Manual ( VII )
- Jun 09, 2018 -

Paint Defects Manual (7)



31.Runs

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DEFINITION

These are beads, droplets, larger globules or "curtain effect" in the paint finish on vertical surfaces.

CAUSES

[1]Paint mixture too slow (hardener, thinner). 

[2]Viscosity too low (too thin). 

[3]Paint or object to be painted too cold. 

[4]Paint applied too thick. 

[5]Too many layers of paint. 

[6]Flash-off times too short. 

[7]Spray-gun held too close to the object. 

[8]Spray nozzle too large.

[9]Irregular spraying action (jerky)

HOW TO AVOID

Ensure that you always adapt the mixture of paint with the correct choice of hardener, thinner and viscosity to suit the temperature and size of paintwork. Ensure that the spray gun is clean and with the correct size of nozzle and air cap. Spray in an even pattern and do not hesitate with the gun or arc your spray pattern.

HOW TO REPAIR

When the paint has thoroughly dried, remove the run with the correct choice of sanding block/denibbing tool using a carbon block or wet sanding paper. The finer the paper, the less damage to the paint and the easier to polish. Polish with a fine polishing Paste and finish with a high gloss polish.


32.Swelling

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DEFINITION

Very slow evaporation of residual solvent from a freshly painted paint process. This causes widespread swelling or sweating of the paint surface. Problem can lead to a reduction of gloss (hazing) and in small areas, edge zone marking (see chapter on “Edge Marking”).

CAUSES

[1]Drying time too short between layers in a complete process and/or too high a film thickness of the filler coat within the process.

[2]Filled areas are too thin or are not sufficiently isolated.

[3]Swelling of solvent-sensitive substrates.

[4]Incorrect quantity of hardener in Body-Filler or Filler coats.

[5]Incorrect process when finishing over NC or TPA substrates.

HOW TO AVOID

[1]Always keep to recommended film thickness and drying times for each product. Where possible dry with infrared as this dries from the lower layers first.

[2]Apply isolating coat in sufficient film thickness (circa 50 µm). 

[3]Before painting, carry out a solvent test with acrylic or NC Thinners.Sand feathered edges and surfaces finely (Body Filler with P80/ P150, Primer Filler with P240 – refer to technical information sheets). Do not apply Body Filler over old paintwork which is solvent sensitive (better to apply to bare metal). Apply sprayfillers in thin spray coats and allow a good flash-off between coats (to isolate). Use products with mild solvent properties (Waterbased fillers). 

[4]Only use specified mixing ratios. 

HOW TO REPAIR

Thoroughly sand back, or remove the affected area. Refinish with the correct primer and/ or Top Coats.


33.Spotting by External Sources

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DEFINITION

Physical attack or discolouration of the paint surface due to various causes; the spots take various shapes, colours and sizes.

CAUSES

[1]Tar - Dirty, brown-black spots.

[2]Industrial waste gas, e.g. SO2 - Large area or spot area gone matt.

[3]Acid Rain - No short-term visual effect, but can go matt.

[4]Acid(Battery) - Usually destroys the entire paint build down to the metal.

[5]Tree Sap - Thread-like and droplet shaped, sometimes clear and sometimes brown-yellow marks with swelling.

[6]Insects - Marks of insect bodies visible in the paint surface.

[7]Insects Secretions - Bee-droppings:long yellow brown marks. Greenfly excrement: round, ring-like etchings.

[8]Bird-Droppings - Appearance can vary depending on the type of bird, weather conditions and duration of contamination.

HOW TO AVOID

Remove all foreign bodies and matter from the paintwork as soon as possible. Wash off tar and tree sap using appropriate cleaner. 

Remove all other contamination with water. Regular paintwork aftercare is required (washing, polishing, wax protection etc).

HOW TO REPAIR

Depends on the amount of damage. For damage to the top-coat, first attempt to polish out the problem using Polishing Paste and finish with a High Gloss Polish. As a second attempt, sand the area with P1200 and then repeat as for the first attempt. For major damage, sand down to a sound substrate and repaint as necessary.


34.Solvent Boil

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DEFINITION

Blister-like surface defects due to solvent entrapment in the surface of the paint film.

CAUSES

[1]Coats applied too thick. 

[2]Hardener and/or Thinner too fast. 

[3]Flash-off time between individual paint coats too short. 

[4]Flash-off time before baking or Infra-red drying too long. 

[5]Insufficient distance between IR lamps and object causing too high a temperature. 

[6]When using a wet-on-wet system, too short a flash off between coats.

HOW TO AVOID

[1]Keep to recommended film builds.

[2]Use correct choice of hardener and thinner for the working temperature available (see temperature table).

[3]Keep to recommended flash-off times.  

[4]When using Glasurit products, no flash-off time is required before baking. 

[5]Keep to recommended distances and intensities when drying with Infra-red. 

[6]Keep to recommended film builds and flash off times between coats.

HOW TO REPAIR

For surface defects caused by solvent boiling, the paint coats must be sanded back to a sound substrate. Refinish using the correct choice of primers and top-coats. If the bubbles are not completely removed, pin-holes will appear when the next coats are applied (see chapter on "Pinholes").


35.Scratches From Car Wash Brushes

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DEFINITION

Thread-like scratches which are often in parallel lines and are particularly visible on darker colours. The surface has a reduced gloss level and appears grey in shade.

CAUSES

Hand wash brush or car wash brushes which are too coarse and/or dirty.

Insufficient pre-wash with insufficient water.

Exposing newly repaired paintwork to a car wash too early. A newly applied coating is less scratch resistant when the paint is not dried for long enough or when too thick a coat is applied or the wrong amount of hardener is used.

HOW TO AVOID

Use suitable and clean brushes.

Thoroughly wet the car before brushing with plenty of water.

Avoid washing the car too quick after it received a new finish (see chapter on "Aftercare of vehicle paintwork"). Keep to recommended film thicknesses, drying times and amount of hardener.

HOW TO REPAIR

Polish out the problem with a fine polishing paste and finish with a high gloss polish. Damage caused by car wash brushes cannot easily be prevented. Some cars are initially supplied with a scratch resistant clear-coat as standard. These cars may be repaired with a scratch resistant clear, which could also be used on other vehicles.