Saturday, 2 April 2016

Orange Peel Removal

Textured Paint (Orange Peel)

Paint Thickness
Using a medium abrasive polish and a rotary polisher will remove approximately   from the paint surface (typically 4 passes at 1500-1800 RPM) but there are many variables such as the abrasive grade of the polish or compound and speed and  pressure used that may affect the paint removed) These numbers should be checked with a paint thickness gauge (PTG) There comes a point when you must judge wither removing a scratch will compromise the clear coat and if so you’ll have to ‘live’ with the imperfection.

A clear coat thickness is approx. 50 - 75 µ a paint thickness reading of 100 µ < (Microns) is reasonably safe for polishing.  80-90 µ I wouldn't use anything stronger than 2000 < grit polish, 70-80 µ 2500 < grit polish and under 70 µ) use a glaze.

If you have reservations about the amount of paint surface removed or the amount of paint coating remaining the use of a paint thickness gauge (PTG) is arbitrary

Note: 1 µ (micron) is 1/1000th of a millimeter or 0.0393700787 Mil or 0.001 of an inch
·         200µ + can be expected on older cars that have been hand painted or a re-painted vehicle
·         100 – 200µ - normal paint thickness
·         80 – 100 µ - thin paint
·         80 µ < - very thin paint

These numbers are offered as a guide only, as there are too many variables to provide any more than an approximation.

Paint thickness will often depend upon the OEM paint specification, which can vary by vehicle assembly plant. It’s interesting to note that painters must now demonstrate proficiency with an electronic paint thickness gauge in order to become certified to perform paint refinish warranty work for General Motors Corp. (GM) vehicles.

Kinetic (or dynamic) Friction
Kinetic friction induced heat is an often misunderstood concept of polishing / compounding; abrasives require friction to breakdown, not heat; heat is just a resultant of friction between two surfaces.

Polishing a paint surfaces transfer’s kinetic (or dynamic) friction induced heat to the paint surface, thermoplastic polymers have both tensile strength and elongation (elasticity) which allow the surface to flex, expand and contract in accordance to surrounding temperatures, solvents, resins and other ingredients in polishes will expand causing the paint film surface to expand.

As the metal substrate expands the paint moves with it, due to its elasticity, thereby becoming elongated (thinner) this is part of the cause of friction induced ‘burn’, you’re applying pressure and an abrasive to a less dense (‘thinner’) paint surface.
Is paint film surface that has a dimpled appearance that paint takes on due to an equipment/operator caused defect?

Technically traditional textured paint  is in the clear coat. It can however be in the base coat usually caused by spraying the paint dry.

There are several factors that contribute to textured paint  – incorrect paint mixture (incorrect reducer for the temperature during spraying or incorrect mixture of paint, hardener and reducer) incorrect  paint-gun pressure and/or distance from panel, poor spray gun atomization, an operator not knowing how to set-up the equipment for that particular type of paint, or even a partly blocked paint-gun nozzle, improper pre-paint preparation and /or paint application, or uneven drying of the clear coat.

It should be eliminated after the final shooting of clear coat by the OEM wet sanding the paint film surface, and polishing with a mildly abrasive polish and a high-speed rotary polisher.
Note that some degree of textured paint  can be found in most finishes, both OEM and repainted.

Textured paint  Removal

Check the paint with a PTG to see how much paint there is available before attempting repairs Clear coat that is too thin loses its ability to adhere effectively (delaminating) to the underlying paint layer and will flake off.

A vehicle with its original paint has a higher re-sale value than a repaint. Due to the above; something else to consider is a ‘do nothing’ option and learn to live with it.
It can be removed by wet-sanding but this entails a substantial reduction in clear coat thickness, which may eventually entail repainting

CarPro Textured paint  Removal Pads - you can now remove or substantially reduce textured paint  in the top layer without sanding. While removing textured paint  and deep defects you are also polishing the paint rather than leaving sanding marks, which reduces the steps needed afterwards.

These pads have a very aggressive abrasive and are deceptive; they have twice the rate of cut of typical wool pads. They don't dull the paint like sanding so it may appear you aren't removing paint but you most certainly are.

They are intended for use by professionals who are very familiar with film thickness, compounding, polishing, and the dos and don’ts of paint correction. Theses pads are designed for use with a rotary polisher, average removal is approximately 5µ (0 .2 Mil) - 7.5µ (0. 3 Mil)

These pads are available in two configurations: Denim (2000 Grit) is the more aggressive and designed for the removal of severe texture from refinished paints and Velvet (3000 Grit) is used for removing light textured paint  from thin, factory-applied paint; both pads utilizing CarPro Fixer as a lubrication / compound.

Use very little pressure and check the paint surface temperature and clean paint debris from pad surface often. Similar to ‘block sanding’ the pad / backing plate are rigid enough that when used correctly it abrades the paint ridges (high spots) faster than the valleys. Either pad will polish the paint as it removes textured paint  requiring only one or two additional polishing steps to create level paint that reflects accurately. These pads should only be used with proper knowledge of clear coat thickness in conjunction with a paint thickness gauge. As with any aggressive abrasion method be very cautious with factory OEM paint.

There are two considerations; (a) how much clear coat (b) how much ultra violet protection can be removed, they are not interchangeable. The following are the maximum allowable clear coat reductions the major USA car manufacturers will allow before the paint warranty becomes void; 0.3 Mil (7.5 µ (micron)

You should initially try these on a test panel and get an idea of just how fast they remove paint. Using little or no pressure (machine weight alone) start a low 600-700 RPM and then progress to 1200 RPM, at this speed the kinetic heat produced by these pads is high so it is wise to constantly check paint surface temperature.

The pad / backing plate combination is rigid and so acts in a similar way to 'block sanding’, removing the high spots before the valleys, maintain the pad flat and parallel to the surface; a spritz of distilled water can be used to reduce the surface temperature, but beware of product spatter

I hope the above article was informative. By having some understanding of the ‘What’ and ‘Why’ as well as the ‘How’ along with a little science to help you understand how the chemicals we use react, you can achieve the results you desire. 

Questions and/ or constructive comments are always appreciated

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