It should be realised that powder coating is a still paint. The difference between powder coating and wet painting is more to do with the application not the end product. It is susceptible to the same marketing pressures as any other product. The quality of the product is proportional to its price. Fading and gloss retention are two areas that are noticeable between the two price extremes. Express Coatings pays on average twice as much for the high quality powder it uses, compared to its cheapest equivalent.
Repair, fading, blemishes and light scratches, to powder coating.
Repair faded powder coating
Faded powder coating means, the surface of the coating has oxidised. This is usually only the surface,
(2-3 microns). By rubbing with cutting compound the surface will be removed and new paint exposed with its original colour. However, if the original coating was a matt finish it will now have been polished to a gloss.
Repair light scratches and blemishes to powder coating.
Scratches may be deeper than 2-3 microns. Use cutting compound to remove the powder coating down to the level at the bottom of the scratch. A fine rubbing down paper may speed up the process (800 to 400 grit, no coarser), but the job will need to be finished with cutting compound to remove the fine scratches left by the rubbing down paper.
Repairs by Aerosol
Cleaning prior to painting.
The original paint needs to be clean prior to ‘touch up, or touching in’ repainting. Indoor components may have been polished with polishes containing Silicone. This will repel any further painting and must be removed from the local area. Clean the surface by washing with a detergent and a scotch-bright. ‘Multi Clean’ is specifically designed for cleaning material prior to painting. Thoroughly rinse and dry. If solvents are needed to remove marks, a soft cloth dampened with Isopropyl Alcohol may be used. Solvents containing esters, ketones, or chlorinated solvents must not be used without consultation with the paint manufacturer, as these are too aggressive and will melt the paint. A small discrete area should be tested first.
The surface contaminants may need to be removed by abrading with fine rubbing down paper ‘400 grit’.
If the component has been damaged, causing chipping or cutting to the paint, the loose flakes should be removed. ‘Ugly steps’ where the paint has been chipped need to be feathered. Course rubbing down paper ’80 grit’ will do this faster, but it will leave noticeable scratches. Finer paper will produce better results, 250 grit paper is a good compromise, (this will wear smooth quickly, so replace it frequently).
When the original paint edges have been rubbed down smooth and a step is not noticeable, remove the dust, apply a light coat of paint/primer, and allow it to dry. This will show how well the area has been prepared. Continue rubbing down and applying light coats, until the edges of the damaged paint have disappeared. Applied properly, at this stage all physical signs of repair can be lost.
Do I need a primer?
If the preparation has exposed the metalwork, for more than four square centimetres, then a primer should be used. A primer is good for filling defects, as it has a high concentration of solids, it will also dry more quickly than a topcoat.
What type of primer?
The primer needs to be a single pack paint (does not need a hardener), dries fast and is easy to rub down. Historically, we recommended using cellulose but it’s use is now restricted due to VOC emissions. This presents a problem, as most paints that do not fall foul of this legislation are not aggressive enough to melt into the powder. They will dry on it, making intercoat adhesion near non-existent.
Easiest way to apply a primer.
The simplest and quickest way to apply paint, including primer, is to use an aerosol. A tapered thickness with out brush marks can be applied, this is a thin coating on the extremities of the repair area, building up to a thick coating where the protection is required.
Application technique for aerosol.
Apply three very light coats and allow each to dry. When the surface has been covered with the new paint, heavier coats may be applied. Do not rush, as this will produce runs; allow two minutes between each coat. The aerosol should never be nearer than 150mm. Continue to move when spraying and keep the same distance from the work piece. Smooth strokes from side to side, covering the local area of damage. Start to move the aerosol before releasing the paint, and before the end of the stroke, stop releasing the paint. This should avoid ridges of paint at each end of the stroke.
On a warm day, if each coat has been allowed to dry before the next application, it should be possible to rub the paint down after about 30 minutes. If it starts to ‘drag and ball’ the paint, leave it to dry further. It will now have to be rubbed right back to a smooth surface again, which may take another hour. More patience is required. (The thinner the coats of paint, the faster they will dry.)
Types of paint.
If a primer is not used then the paint must have an aggressive solvent that will melt its way into the powder coating. An indication of suitability is the speed it takes to dry. Household polyurethane, which takes 24 hours to harden, is not suitable. This will sit on the powder, instead of melting its way into it. The result is, it will peel off. It is always good practice to mechanically abrade a key by using rubbing down paper, or at least use a Scotchbrite. A small discrete area should be tested first.
Don’t hesitate to contact us for a quote on your powder coating repairs or for further information.