Can Washing in Direct Sunlight Damage Your Paint?

Prepare yourself for an embarrassing amount of myth busting.

The number one concern we hear from novice detailers and at home detailing enthusiasts is around washing in direct sunlight...

From social media comments to reddit posts, the concern is so loud you'd think that detailers are in fact, vampires. Absolutely horrified by the idea of washing a car in direct sunlight. Well... I can tell you that we are not vampires (at least the one's I know). It's just that some people like to take suggestions and risk aversion to the extreme and the public tends to be a little dogmatic and uneducated when it comes to chemistry.

So let's get clear on what the sun can and can't do to your paint, and whether or not this is something you should even be concerned about.

How Can The Sun Cause Problems?

From a scientific and practical standpoint, sunlight is effectively a problem for two reasons:

1. Heat

2. UV Radiation

And these cause 3 problems to be concerned with:

1. Chemical reactions

2. Dried product residues

3. Water spots

All of these problems are closely related too! Let's address these quickly and logically.

1. Chemical Reactions

Heat and UV radiation can both act as a catalyst for chemical reactions. When involving sunlight, these are typically referred to as "Photochemical reactions" and they involve the absorption of light energy into a chemical substance. Regardless of the pathway, the problem we're worried about is essentially, corrosion. Corrosive substances, along with heat and UV radiation, can damage clear coat.

Although, time is still a necessary component in any reaction, so a problem only arises when a substance remains on your paint over many hours or days in direct sunlight. Typically the substance is acidic, like bird droppings or bee poop (those little yellow pollen drops are actually bee poop), and stick to your paint.

When it comes to washing your car, photochemical reactions with already "paint safe" products is not a problem because they are not corrosive. The above examples are usually mitigated by washing itself, because you are removing the bird droppings etc while washing!

2. Dried Product Residues

Heat from the sun causes water to evaporate from products and they dry on the surface of your paint. This can cause residues to stick around from the dried substances, that if not rinsed or removed entirely, potentially could cause damage from photochemical reactions. Although this is rare as most products are already paint safe and aren't reactive to sunlight, and some are supposed to leave residue! In fact that's the entire point of a coating or sealant.

Soap is typically the problematic substance that you want to avoid letting dry on your paint because it can cause streaks that are frustrating to remove due to the residue, or even the product removing waxes and sealants that protect your paint. We'll share the fix for this at the end. 

There is no scientific evidence to point towards any non-acid soap causing any damage to clear coat due to corrosion in reaction to sunlight. Dried product residues are mostly frustrating, rather than harmful. You will read many bogus articles on the internet about this with no science to back their claims, unless it's an acid based cleaner (again, acids tend to become more corrosive with exposure to sunlight).

3. Water Spots

Does this need an introduction? I'm sure we've all dealt with frustrating water spots forming on our paint. Contaminants and minerals in water are left behind when water dries on our paint. This is a more interesting problem imo because it's not as straight forward, and there are A LOT of myths around this.

Minerals from hard water, or to put simply, "salts", are not corrosive to clear coat. They react with bare metal to accelerate rusting, but that is a different process entirely. Although... problematic.

In theory, heat and water cause clear coat to swell and expand and the microscopic texture or "porous" surface of the clear coat "swallows" up these minerals and they essentially become part of the clear coat as an imprint. This could be closer to "erosion" rather than corrosion if the clear coat collapses or becomes brittle over time due to the water spotting. It's ugly for sure because it can become "permanent" and require paint correction.

But for myth busting sake, the only corrosion occurring is unlikely, and due to salts and water get down through the paint to cause corrosion of the metal beneath. You can see this with paint bubbles that flake away to reveal rust and corrosion on the panel on older cars, but this usually occurs from cracked panels and edges, not from water spotting.

What should YOU be concerned with while washing at home?

Ok so to recap and summarize here's what can really happen when washing in the sun:

You can end up leaving soap on your paint long enough for it to dry up and cause streaks. These streaks can be difficult to remove. Then when you go to rinse the car, hard water spots can form quickly before you dry. These are also frustrating AND important to remove as they can damage paint over a long period of time. Then a lot of products and detail sprays that you would use to dry the car or shine and protect, can also become very stubborn, streaky, and tacky in the sunlight, further slowing down your process.

Let's say you clean this up and your car looks good afterwards, regardless of how frustrating it was. Now, was any harm done because of sunlight?

Likely, no. Not at all.

So what happens if your products don't suck?

What if they work well in the sun because of technique and formulation?

Hear me out:

Sunlight can actually make detailing outdoors easier because you can see what you're working with and NOT leave any hard water stains behind because you didn't miss a spot! Obviously, an indoor detailing bay with proper lighting is WAY better for this, but we don't all have those at home, do we?

Heat from the sun can also assist in speeding up the drying process, regardless of hard water spots.

Sooooo... if you rinse your paint with cool water FIRST to reduce surface temp (always do this), then you have a strong soap that isn't corrosive, like our Step 1: Wash, and a pressure washer to remove the soap that binds to the dirt on your paint, even if it becomes a little dry... then the soap is removed entirely without streaks. You can also re-foam the car with some more soap if you need to remove soap residue because you took too long. Simple fix.

Then once the car is dry, if you use our Step 2: Dry spray, it crushes hard water stains, and it is formulated to be extra pliable as it dries so you can level the residue and shine it even in the sun, without sticky, tacky streaks.

I personally have gotten excellent results washing in direct sunlight on 90 degree days with our products. Is it ideal? No. But is it dangerous or bad? No, not really.

Honestly, the best way to wash outdoors is not always in the cold or in the shade, as that can make drying the car and shining it, very slow and frustrating because you missed man spots you couldn't see. It can be a lot easier and faster to wash on a cooler sunny day, or on a slightly over-cast day when the sun is not raising your paint surface temp so much. I enjoy morning and evenings when the sun is lower for best results.