This guide focuses mainly on spray techniques, but also touches on some touch-up paint problems.
Touch-up paint problems:
The most common issue with touch-up pens or bottles is that when the topcoat or laquer is applied, the base colour and clear/top mix togther. You definitely do not want this to happen and you'll be left to start again if it does. The most important part is make sure the area is cleaned very well with Wax & Grease Remover to prepare the surface. At the very least, use rubbing compound to clean the surface.
After applying the base, let it dry for at least 2-3 hours and preferably overnight if possible. Then lightly dab the top colour on. Before applying the top colour or laquer, make sure you already have paint on the tip of the brush. Do not rub the brush on the area you are covering, just lightly dab it. If the color does not look exactly correct, you may have to add another light coat. To do so, just repeat the above instructions.
Spray Application Problems:
The following list covers just about every type of application problem that can come up.
Low Gloss after laquer is applied
Microscopic roughness of the surface, which may result from:
Poor hold out of primer, or the application of topcoat over primer which is not thoroughly dry
Poor quality or incorrect thinner, or the use of additives in the paint.
Incorrectly prepared or poorly applied paint.
Application over a poor substrate
Excessively slow drying due to high humidity or low temperature.
Solvent fumes or exhaust gases attacking the surface.
Surface contamination by wax, grease, oil, soap or water.
The use of strong detergents or cleaners on a newly painted surface, compounding too soon after painting or using compound which is too coarse.
Use an approved primer, and allow to dry thoroughly before applying the laquer.
Use only recommended thinner and approved additives.
Ensure that the paint is stirred thoroughly, apply under the correct conditions using proper spraying techniques.
Prepare the substrate thoroughly.
Ensure that the paint dries under warm and dry conditions.
Ensure good, draught free air over surfaces while drying.
Wipe the undercoat with solvent and dry thoroughly before applying the topcoat.
Avoid using strong detergents or cleaners on newly painted surfaces. Do not compound paint until thoroughly hard and always use the correct grade of compound.
Normally the shine may be restored by rubbing down with abrasive compound and polishing. If the dulling is too severe for this to yield satisfactory results, rub down the topcoat and repaint.
Dirt in Paint
A rough, irregular surface to the paint film is easily felt with the hand. The particles are often totally embedded in, and covered by the film.
Cause Contaminating particles incorporated in the paint.
These may be the result of:
Dust, dirt or threads falling from cloth or clothing or blown out of mouldings or panel joints during spraying, setting on the wet paint film.
Dust not properly removed from the surface prior to spraying.
Airborne particles setting on and becoming incorporated in the paint film during or immediately after spraying.
Dirt in the paint or thinners resulting from open or rusty cans.
Ensure that cloths and clothing are clean and dust free, blow out mouldings and panel joints prior to spraying.
Clean down and tack-off the surface prior to spraying each coat.
Keep the spray shop clean and dust free, avoid sanding operations in the area of the spray booth. Wet down surrounding surfaces if necessary, ensure that the filtration system is working properly.
Keep all materials in clean, sealed containers and strain before use.
Allow the paint to harden completely. Light surface dirt may be removed by flatting, compounding and polishing.
Deep embedded dirt, or dirt in synthetic paints, requires the surface to be rubbed down until smooth and repainted.
Failure of the paint droplets to coalesce on the surface.
This may be due to:
Poor spraying technique, spray gun too far from surface, incorrect compressed air pressure, incorrect nozzle adjustment.
Excessively thick or thin film.
Paint incorrectly mixed, wrong viscosity, poor quality or incorrect thinner.
Insufficient drying time between coats, cold air fanning to speed drying.
Incorrect ambient or surface temperature, draughts.
Use the correct spraying technique and ensure that equipment is correctly adjusted.
Apply paint in thin even coats.
Ensure that the paint is correctly mixed, use only recommended thinner with the correct grade.
Allow sufficient drying time between coats.
Spray within the recommended temperature range and ensure proper ventilation.
Rub out the orange peel, compound and polish. In severe cases it may be necessary to flat and repaint the surface.
Lifting or Bubbling
Non uniform drying within the paint film.
This may result from:
Excessive film thickness.
Insufficient drying time between coats, forced drying, non uniform air temperature.
Use of wrong or poor quality thinner.
Apply paint in thin, even coats.
Allow sufficient drying time between coats, ensure correct, uniform drying temperature.
Use only recommended thinner.
Allow the film to harden thoroughly. If the defect is slight, flat, compound and polish the affected area.
In severe cases rub down to the substrate and repaint.
Runs or Sags
Well defined local thickening of the paint film in the form of a wavy line or shallow, rounded ridges, normally confined to sharply sloping or vertical surfaces.
Slumping of the paint due to:
Excess thickness of application, air pressure too low, fan width too narrow, spray gun too close to the surface or moving too slowly.
Use of poor quality or incorrect thinner.
Incorrect viscosity of the paint.
Air of surface temperature too low.
Contamination of the underlying surface.
Use the correct spraying technique and spray gun settings.
Use only recommended thinner.
Ensure that the paint is mixed to the correct viscosity.
Always spray within the recommended temperatures.
Ensure that the surface is scrupulously clean.
Allow the paint to harden thoroughly, rub down excess paint, flat, compound and polish. In severe cases it may be necessary to rub down and repaint the surface.
Note: Due to separation of the metal flakes, metallic paints will normally require repainting.