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Everyone, especially people who love washing and waxing their cars, has been telling me about the long-term benefits of regular waxing. They tell me that the layer of wax acts as a protective shell and will prevent contamination (such as UV radiation, bird droppings, tar, etc) from "burning" into the car's paint. As a consequence the car's paint would keep it's good looks longer, and ultimately the car would even have a higher resale value.

I find that hard to believe. I don't know anything about chemistry so probably my thinking is not making sense at all, but the way I see it is that car waxes contain a number of natural and less natural ingredients but basically I think every car wax is in fact just grease. So you put a layer of grease on you car, which indeed makes it shine more and causes water to not stick as much to the paint. But I have a hard time believing that this thin layer of grease is going to cause any long-term beneficial effect. I bet if you wash the car regularly, that after 5 times the wax is simply gone and even if it does stay on the car, can this really have a significant protective effect? If yes, I would like to understand how.

The problem I have is that everyone who is telling about the benefits only refers to personal experience. Is there any real scientific and independent test result that proves these claims?

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    Modern car paint has final a clearcoat layer. I'd not be surprised that wax fills the minor scratches in this layer. Nov 2, 2021 at 16:18
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    Also wax is not grease (as you claim). Try washing a honeycomb with water and even soap, see how fast it's "gone". (Sure it's not acrylic or polyurethane like the clearcoat either.) How much actual wax those car wax products deposit is a different matter. Nov 2, 2021 at 16:40
  • Looking e.g. at some 3M "wax" product, it says it contains a polymer (not detailed what though), so I suspect it's really more like (clearcoat) paint than actual wax. Nov 3, 2021 at 7:15
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    I bought my first car in 1971. In the 50 years since, I've almost never waxed nor washed any of the cars I've owned since then. Never have I ever felt that I should have spent the time, effort, or money to do so. Nov 4, 2021 at 1:23

2 Answers 2

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+100

Partial answer only.

Wax doesn't protect the car from acidic rain:

Does wax protect from acid precipitation: Waxed automotive finishes in the Acid Dew and Fog Test, SCHULZ U.; ZWICK W., European Coatings Journal 1997, no9, pp. 784-790

Tests with seven different wax recipes and two current types of coating showed that wax on coating surfaces is not a barrier against acid atmospheric precipitation. Waxing can both slightly inhibit and enormously increase the harmful effect of aggressive precipitation on the coating.

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    I was curious about where acid rain falls -- you might add that to your answer (wiki on acid rain affected areas for one starting point). The current answer won't be relevant for areas unaffected by acid rain.
    – Hendy
    Sep 5, 2011 at 21:01
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    actually, it's quite relevant as it debunks one of the claims made in the original question (bird droppings work similarly to acid rain on the paint of your car, them being highly acidic).
    – jwenting
    Sep 6, 2011 at 6:42
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    I am not sure this counts as a signifigant reference seeing as all of the important information is behind a paywall. There is nothing included here about the methodology or the control.
    – Chad
    Sep 9, 2011 at 13:22
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    @Chad, there is a meta-question on this issue, which is probably a better place to discuss this.
    – Oddthinking
    Sep 10, 2011 at 0:47
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    @Chad, I absolutely agree that acid rain is but one of the issues, and that this answer falls short. I started by saying it is a "partial answer"; I hope someone who has more luck researching this topic will incorporate it into their canonical answer. I would feel embarrassed by the current upvotes, which are probably more than it deserves, but I marked it as a Community Wiki when I wrote it. Your point about the abstract not containing enough info is an interesting one - and one I think should be made for everyone to discuss on the meta-question, rather than here.
    – Oddthinking
    Sep 13, 2011 at 0:49
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Car paint is a very mature industry. There is two main ways a color coat can suffer: the color can change, e.g. bleach, and the surface can erode. An eroding surface optically adds white to the color beneath by adding diffuse reflection (think about a glossy CD-cover that has a black booklet underneath - if the cover is scratched the booklet will appear greyish, not fully black anymore) - this does not mean that the actual coloring agent is bleached, modern cars colors don't do that anymore, generally, it is just the color plus the diffuse reflection of the eroded surface of the covering, clear, layer. Buffing up that surface with wax will 'make the colors more vibrant' by reducing the diffuse reflection (changing it to specular reflection, i.e. mirror-shine). The wax does not actually do anything to the pigments themselves.

To really ruin the color, the erosion would have to progress all through the clear coat, to the color layer itself. Neither is that realistic, nor is the wax going to be much hindrance, if the environment really is that bad.

As wax does not hinder the influence of vapors, the only big effect to stop would be photooxidation/-degradation of the coating. As the coating is ideally very thin, on the order of nanometers the absorption of UV would have to be phenomenal to make a dent in the incoming radiation. The clear coat with its many micrometers of thickness would be a much more appropriate venue for anti-UV measures. It would need to reflect, so a UV-spectrum photo of a half-waxed car woul be the clincher.

EDIT: I found an interesting video on YT (results at 11:30) where a garage owner does some testing of clear-coat/sunscreen/various waxes and 'ceramics' regarding the UV-protection they offer. The amount of thought he put into his test setup is heartwarming, though he does not, for instance, control for thickness - result: Clear-coat does serious UV protection, waxes do not.

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  • your answer could be great but some links are broken and you adding quotes from the linked articles will save the reader long searches and misunderstandings. One thing both answers missed are possible benefits towards “cleanability” which doesn’t contribute directly to longevity but might help in reducing dirt and contamination thus reducing eroding for example (all speculative by me due to lack of proof)
    – Rsf
    Nov 3, 2021 at 19:53
  • @Rsf can you tell me which ones do not work for you (click edit on my post, and then tell me the number (1-7))? - I tried them all just now, and they work for me.
    – bukwyrm
    Nov 4, 2021 at 21:19
  • "environment really is that bad." and "on the order of nanometers " are non existing, " appropriate venue for anti-UV measures" is just an abstract
    – Rsf
    Nov 9, 2021 at 9:11
  • @Rsf thanks for the catch, it depended on the login - tried to fix
    – bukwyrm
    Nov 9, 2021 at 9:22

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