Automotive paint (urethane) is classified as a semi-permeable thermo-setting membrane; that is it moves in unison with its metal substrate, this is termed as elasticity (tensile strength and elongation) a paint surface is often subjected to high ambient temperatures, which cause a temperature swings in excess of 40.OF. A paint surface must remains flexible while retaining its tensile strength, to enable it to expand and contract, following any temperature fluctuations of the substrate, elasticity is imperative; otherwise the paint film would crack.
Some harsh solvents (especially chlorinated versions) lacquer thinner, xylene, toluene, acetone, Methyl ethyl ketone along with Butyl cellosolve will negatively impact the paints resin binder system and swell the paint substrate, this may take some time to materialize
The main risks associated with using solvents; relate to the effects of solvent on the organic binder system that holds the paint together. The more acute element of risk is that of expansion of the paint through sorption of solvent. The polymerised urethanes dried oil network may not be truly soluble, but the polymer network may expand by sorption of solvent or concentrated isopropyl alcohol molecules and sometimes silicone.
Depending on the degree of expansion, the paint will be more or less softened and its capacity to bind the pigment particles may be affected. In the swollen condition, there is a risk that pigment may be removed from the paint through the (kinetic energy (friction heat) of a foam pad and rotary action (twisting) causing the paint to tear.
OEM or freshly applied solvent-based paint once its cross- linked forms a very tight matrix; meaning it's not a porous as many people seem to think; however time and environmental damage, especially brake dust particulates that act as a conduit to the paint matrix, cause micro pores and fissures that allow permeation.
Dependent upon the particulate size, some chemicals penetrate easily, only liquids that are smaller on a molecular level than the cross-linked paint can be absorbed; solvents and alcohol can permeate the paint causing the paint to temporarily swell hiding surface scratches and marring
Freshly Applied Paint
Freshly applied paint that in the outgas stage, is still full of evaporating solvents, and is usually less dense (soft) despite the additives used (hardener) once a catalyst, kinetic energy (friction heat) is added, it causes the paint film to expand, temporarily hiding scratches, this is often the reason for a body-shops bad reputation of returning vehicles that have sanding scratches in newly applied paint that should have been removed.
Be cognizant when polishing newly applied paint the kinetic energy (heat) from a foam pad can also cause solvent engorgement, which causes the paint film to thin due to the expansion of the evaporating gases, applied rotational force may also cause the paint to tear Kinetic friction (heat) is transferred to a solvent (IPA or fresh paint) causing it to both expand (Charles' law (also known as the law of volumes) the paint film and soften it.
Automotive paint is classified as a semi-permeable membrane; it has both tensile strength and elongation (elasticity) newly painted surfaces are soft and full of out gassing solvents, resin binders and additives, as well as and water.
Polish contains solvents, which soften the paint film, kinetic surface friction and applied downward pressure transfers its energy into heat / torque (force to rotate an object about an axis), which could result in the alteration of the paint films bond between its substrate, causing it to delaminate or tear?
The heat makes the gasses expand (pV = nRT) the expanding gases go through a phase transition (change in density) and to relive this increased pressure they (a) rupture the paint film surface, causing small fissures (similar to solvent pop)
The heat may cause the gaseous vapours to expand, but not enough to break through the hardening clear coat. Once the vapour has evaporated, it may leave a void between the basecoat and the clear.
Therefore you have a cloudy spot where the clear and base is no longer adhered together. If this is the case, the clear coat will delaminate in the future.
Coatings (paint) becomes a semi-solid permeable membrane, Being a polymer (elastomers) it remains flexible while retaining its tensile strength, to enable it to expand and contract to follow temperature fluctuations of the substrate (elongation) kinetic friction and its associated heat can cause a rapid temperature rise (i.e. initial surface temp 80.oF, heat attained with a cutting foam pad at 1,100 RPM for approx. ten seconds is approx. 104.oF) the paint temperature can be checked by utilizing an instant read-out infra-red ‘gun’ thermometer, paint surface ‘spot’ temperature should be limited to <110.oF
In accordance with the Society of The paint temperature can be checked by utilizing an instant read-out infra-red ‘gun type’ digital thermometer. In accordance with the Society of Automotive Engineers (SAE) a localized (spot) temperature should be limited to of 115.oF (range 105 – 145. OF.
Dependent upon paint specification, thickness, and etc) as it will cause the paint to soften and the resin binder system to eventually fail Be cognizant that with high ‘spot’ temperatures the foam pad will cause scratching that is forced deep into the clear coat.
Above >115.O F and you create what the coating industry calls "thermal stress" - those long, small cracks in the paint that looks like light scratches, but cannot be removed by buffing. This phenomenon won't show up at first, but in a year or so the cracks will be evident. (See also the first law of thermodynamics et al)
Surface Filling (Drop back) / Masking Abilities
Filling or ‘drop-back’ can also be caused by the paint swelling, solvents are heated and expand, thereby temporarily covering any surface imperfections
Typically when people talk about fillers in compounds/polishes that are not removed will temporarily mask defects. Once the surface is washed the ‘filling’ will be removed, and revelling the lack of true paint correction.
This is generally termed ‘drop back’, they are generally a by-product as they are included into the formulation to provide surface lubrication (glycerine, wax, mineral oil, and etc) or silicone- based oils that are far harder to remove (but that’s another subject) These lubrication agents can leave a slight film which might help (by filling) to hide minor imperfections or swirls, but they don't bond to the paint. So once the surface wipe-down process is used they are revealed
Depending on the manufacturers requirements the oils can be various grades, the denser the oil the harder they are to remove with a solvent-based wipe down. With these thicker, denser oils using 10% d-limonene based detergent (P21s Total Auto Wash) with the diluted isopropyl alcohol and distilled water solution will remove them
a) Some polishes contain specific products (i.e. Kaolin (china clay) or Diatomaceous earth) that are formulated into the product to (a) burnish the paint surface (b) mask surface defects not removed by polishing (evidenced by excess dusting) (c) or to bulk up the product; this type of filler will also be removed by the IPA wipe-down(s) process
b) Abrasive polishes once they become micro sized by friction will fill the micro fissures in the paint, acting as a filler; a simple wipe with a towel will only help to evenly spread them. This can be alleviated with an IPA wipe-down(s) process
c) Another thing to consider is the use of high tech spray-able silicone polymers. These polymers can be applied at a car wash or used by detailers in spray waxes, quick detailers or spray wax product and can have a lasting negative impact on a paint finish by affecting the performance of compounds and polishes, much like silicone on a paint surface i.e. filling surface scratches as opposed to the polish actually removing them. A proper wipe down process will eliminate this
Typically when people talk about fillers in compounds/polishes they are a by-product as they are included into the formulation to provide surface lubrication (glycerine, wax, mineral oil, and etc) or silicone- based oils that are far harder to remove (but that’s another subject)
These lubrication agents can leave a slight film which might help (by filling) to hide minor imperfections or swirls, but they don't bond to the paint. So once the surface wipe-down process is used they are revealed. ((See also “A new perspective on paint defect return” – by Jason Rose)
Cleaning a Paint Surface with a Solvent
Sorption [: refers to the action of absorption or adsorption];
Absorption [: the incorporation of a substance in one state into another of a different state (e.g. liquids being absorbed by a solid or gases being absorbed by a liquid)].
Adsorption [: the physical adherence or bonding of ions and molecules onto the surface of another phase (e.g. reagents adsorbed to solid catalyst surface)]
Use caution when cleaning a paint surface with a solvent as it negatively affects the binder system allowing sorption through the surface fissures (micro pores).
There are two main risks associated with using aromatic hydrocarbon solvents; both relating to the effects of solvent on the organic binder of the paint. The possible extraction (leaching) of low-molecular weight components of the paint binder by the action of the solvent and heat
The more acute element of risk in cleaning, however, is that of expansion of the paint through sorption of solvent. The polymerised urethanes dried oil network may not be truly soluble, but the polymer network may expand by sorption of solvent or concentrated alcohol molecules and silicone.
Depending on the degree of expansion, the paint will be more or less softened and its capacity to bind the pigment particles may be affected. In the swollen condition, there is a risk that pigment may be removed from the paint through the mechanical (friction) action of a foam pad.
3M™ Prep Solvent-70 (#08983) is a low VOC, water- based ‘safe’ solvent used to remove oils, wax, grease, and silicone from surfaces prior to the application of a coating.
Effectively cleans metal, primed metal and painted surfaces. Use with 3M™ Panel Wipes (#4567) the Panel Wipes have excellent absorbency and are super strength when wet or dry. They are easy to carry and are supplied in an easy to dispense box.
[Anhydrous Isopropyl alcohol [Molecular formula C3H8O] for all-purpose cleaning, isopropyl alcohol, is a colourless liquid with a pleasant odour, and is highly flammable. A miscible clear fluid, Flash point 53.0F (12.0C) closed cup]
Made from 70 to 95% ethanol, or ethyl alcohol, along with water, acetone, methyl isobutyl ketone, and additives to give it a bitter taste, some rubbing alcohol includes perfumes or artificial colouring. Reagent Grade Isopropyl Alcohol, is a chemical grade of highest purity (99.8%) that meets or exceeds purity standards set by the American Chemical Society (ACS) and meets essential laboratory requirements
The term "rubbing alcohol" has become a general non-specific term for either isopropyl alcohol (isopropanol) or ethyl alcohol (ethanol) Rubbing-alcohol products can leave a residue behind It is prepared from a special denatured alcohol solution and contains 97.5-100% by volume of pure, concentrated ethanol (ethyl alcohol) or isopropyl alcohol (IPA)
For less dense (soft) clear coat, the lower rate of isopropyl alcohol dilution (1:10) is recommended; conversely denser (hard) clear coats should use a higher dilution (1:25); as you increase the dilution rate of isopropyl alcohol its paint softening effect drops exponentially.
Isopropyl alcohol is a fast evaporating solvent and at higher ambient temperatures will filly evaporate (flash) within ~30minutes at higher temperatures. At greater dilution percentages it will evaporate more slowly, bear this in mind in warmer environments.
A recommended isopropyl alcohol (IPA) dilution of 1:10-25 (10-25%) in distilled water as a ‘safe’ surface wipedown cleaning solution. The reason for this wide range is due to the variations in the clear coat paint systems
Isopropyl alcohol (IPA) and or other solvents will permeate the paint, causing it to both soften and produce some swelling. Depending on the solvent (strength) and the amount of heat the degree of swelling varies. (See also “Paint (Solvent / Alcohol) Swelling”)
Isopropyl alcohol (IPA) is readily available and like acetone, it dissolves a wide range of non-polar compounds. It is also relatively non-toxic and evaporates quickly. Thus it is used widely as a solvent and as a cleaning fluid [Wikipedia]
Mineral oil can be used to clean heavier oil stains by diluting and liquefying the other oils, rendering the oils more accessible to detergents.
Likewise, it can be employed to de-gum, to remove adhesive residue left by adhesive tape. Be cognizant that while it can be used as a solvent cleaner it can leave a residue, which is undesirable for paint cleaning applications.
Denatured alcohol (or Methylated spirits) - is ethanol that has additives to make it more poisonous or unpalatable, and thus, undrinkable. Do not use denatured alcohol as a substitute for Isopropyl alcohol (IPA)
Potable water usually contains a number of microscopic contaminants (turbidity) along with dissolved minerals such as calcium and iron. Distilled water should ideally be nothing but hydrogen and oxygen molecules and virtually all of its impurities are removed through distillation, which involves boiling the water and re-condensing the steam into a clean container (pH 6.0 – 7.5)
Any dissolved solids such as salt, bacteria, calcium or iron remain solid while the pure water converts to a much lighter steam and is drawn out for condensation, leaving most if not all solid contaminants behind. Distilled water is preferred for dilution as it’s a ‘known’ quality, unlike domestic potable water
In larger chemical and biological laboratories, as well as industry, cheaper alternatives such as deionised water are preferred over distilled water.
Application - fill a fine misting spray bottle with a 1:10 solution (Wurth Citrus Degreaser or P21S Total Auto Wash) / distilled water, and then spray the surface you have just polished and allow the solution sit for approximately 15 seconds.
Agitate the area with a clean panel wipe or a soft 100% cotton micro fibre towel (you may need to repeat this process) change the towel to a fresh quarter after each panel to ensure oil and debris are not re-deposited and observe. This should have removed any wax or oils that may have filled any remaining swirls and show the true post-polish surface condition. If a diluted IPA solution doesn’t remove the surface oils perhaps a specific paint preparation product, i.e. CarPro Intense Oil & Polish Cleanser or DuPont PrepSol II™ may be more suitable
Now using your surface inspection light, shine the light directly on the panel and look for fine swirls. If they are still present, you should be able to see them. If not you will see a clear bright reflection from the panel with a great shine, and clarity