How to Clean Chalked Paint Prior to Graphics Application

As paint weathers in sunlight (UV light attacks and degrades the resin that binds the paint ingredients), it oxidizes and gradually erodes, leaving a powdery, white residue.

Chalking should not cause alarm — it’s the result of the normal aging process. All oil-based paints chalk. Excessive chalking, however, can be a problem, often caused by excessively thinned paint. Very light coats of paint and poor quality paints are also more prone to excessive chalking.

Typically, chalking is not an issue because the white powder is flushed from the vehicle surface during regular washings. However, if chalking remains on the substrate, it must be cleaned prior to graphic applications to prevent a vinyl failure. Chalk contaminates the adhesive and forms a barrier between pressure-sensitive adhesive and the paint, preventing a good bond.

The degree of chalking and the substrate’s condition differ from vehicle to the next — strict rules for substrate preparation don’t exist. That’s why chalking removal may require experimentation.

Some experts suggest using a power washer to flush the surface with clean, warm water, while others contend that even high-pressure power washing only removes a minimal amount of residue.

If you opt to use a power washer, exercise extreme caution. Excessive water pressure can literally blow paint off a trailer panel. Be sure to keep the tip of the washing wand at least one foot from the surface.

Using solvents for cleaning, as I describe in my story 3-Step Prep for Vehicle Graphics, will satisfy the cleaning requirements for most vehicle graphics applications. It does a great job cleaning dirt, grease and tar, but it won’t touch a surface which is badly chalked. In fact, if you try to wipe down a chalked surface with petroleum-based solvent, such as Prep Sol™ you will likely do more harm than good.

A chalky surface is a layer of dead paint, which will absorb the solvent like a sponge. Rather than cleaning the surface, the solvent will turn the white powder into a white paste, which will merely smear around the paint surface. Some chalk and dirt will be driven back into the paint, and the chalk will float back to the surface, causing adhesive failure.

Abrading the surface is often the best — although certainly not the easiest — solution for cleaning a chalky substrate. Many decal installers use a kitchen scouring pad, such as a Scotch-Brite™ pad, and water to clean the surface. This will require plenty of clean rags to mop up the considerable mess.

Scouring pads effectively abrade chalk from the surface, but they will also scratch. In most cases, the result should be acceptable, considering that excessive chalking isn’t aesthetically pleasing in the first place.

Some installers use polishing or rubbing compounds to remove chalking. Be sure to select one without wax, because such cleaners leave a residue that can compromise the adhesion. I recommend using powdered cleaners with mild abrasives. In addition to removing the dead paint, these cleaners will scuff the paint, providing more surface area to bond the adhesive.



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