Stuff you need to know
First and foremost, a pressure washer. But why?
Firstly it saves water in comparison to washing with a hose. Secondly we need to pre-rinse the car to prevent scratching and marring of the painted surfaces, and yes that includes the wheels, most are clear coated just like car paint. The best known way to pre-rinse is by foaming a dry car with surfactants. This will prevent scratching during the washing process. This means that the other piece of equipment ya need is a foaming lance or gun, foamer for short. After the pre-wash foaming dwell time, you rince.
Then you need a foaming soap or also called a shampoo. Be careful and considerate when choosing such. Lots of shampoos for car washing are marketed as pH balanced. The question is, pH balanced to what? Remember pH balanced is relative to some other pH level. Do not confuse pH balanced to pH neutral, two wildly different properties.
Let’s talk about water briefly. Water, that is clean, potable and drinkable is normally around pH 7. This is pH neutral. The quality and hardness of the water is super important. You want a soft and low mineral content water, low or Zero TDS. The reason is simple, low mineral content allows for a good quality foam. Hard water with high mineral content will use up some of the soap to deal with the minerals, leaving much less for the soap to do its work on the surface. Hard water with high total dissolved solids (TDS) will leave the minerals behind when the water evaporates, then waterspouts appear.
The human skin for example, on average, is somewhere around pH 5.5. Water at a pH of 7 is around 15 times more alkaline. Water is also a very good solvent. So then, water is not pH balanced to your skin. Let’s look at good old bar soap, normally a pH of 9-12, so much much more alkaline than water or your skin.
Most soaps are alkaline in nature to be able to clean. Soap is an excellent cleaner because of its ability to act as an emulsifying agent. An emulsifier is capable of dispersing one liquid into another liquid that will normally not allow this. Think about oil and water, they do not mix. This means that while oil, which attracts grime and dirt, naturally does not mix with water, soap can suspend oil/dirt in such a way that it can be mixed and suspended in water, and then removed safely.
Soap is thus a chemical that is attracted to both water and oils and grime. The structure of soap breaks down grime and surrounds it. Soap is not attracted to itself in water, so stays dispersed in water. And this is how soap cleans, by breaking down oils and grime and surrounding them to allow the dirt to float away on a layer of soap. Hence, pre-wash foaming and rinse, before any contact washing ever happens.
Since we do not know the nature of the grime and oils on the car surfaces, pH balance is a moot point, since we do not know the pH of the surface. What we do know is that there are oils, dirt, bird bombs, soot and other industrial fallout on the car. Vehicle oil leaks, diesel leaks and other oily substances are plentiful on the roads. Also oils, soot and engine exhaust products from blow-by and leaks are deposited on the car. Therefore, reason dictates that higher pH soaps will do a better job of emulsifying the grime and floating it away safely.
When do scratching and marring of paint happen?
When the car is being driven, or parked outside or under a tree or where you have the potential of bird bombs or industrial fallout or acid rain.
When is the car at its dirtiest?
Just before you want to clean it. So then logic dictates that when you start washing, you are at the greatest risk of marring or scratching the paint clear coat. How to best deal with this?
We need to protect the paint from this marring and scratching. But how? There are a few ways we can achieve this: Firstly by encapsulating the particles and dirt or other foreign materials in some form of surfactant, or soapy foamy layer. Secondly, by allowing the lubrication from this soapy foamy layer to carry the particles above the paint layer and prevent contact between itself and the paint while it is moving.
Contact washing or using a stream of water at this point prior to the pre-rinse, will be damaging as everything clings to the paint. It is not yet suspended above the paint, the reason for a foamy pre-rinse.
Think of it this way, if you use sandpaper, you have particles abrading a surface. If you sand the layer of air just above the surface, there is no contact with the surface and no sanding or abrasion can happen. If you have loose abrasive particles on paint, you want to lift them from the surface and coat them with a soapy and foamy layer that is slick and will slide the particles across the surface with no contact.
This is how, when the risk is biggest, you prevent scratching and marring of the paint. Rinsing is and should be the second thing we do when washing a vehicle. After Foaming, give the surfactants time to break the bond and lift the grime from the surface and carry it away. Coating the grime and preventing contact between the grime and surface while moving, is the key..
Something to consider is a controlled environment as best you can.
We want as little as possible air movement or wind, as cool a panel as we can, close to ambient and no direct sunlight. These things will severely reduce contact time and we need a good longer contact time.
So step one is to wash the dirtiest parts of the car, the wheels and engine. You can pre-rinse those in exactly the same way and as part of your general pre-rinse. Let it dwell or if you choose, use your wheel and tyre cleaner over the foam per directions. I would advocate for a pre-rinse of the car with foam and include the wheels and engine bay. Then rinse the foam and tackle the wheels to get them clean. After that would be the engine and engine bay. Pre-rinse, then wash down. Now start to contact wash the engine and engine bay. When done with that we can start the exterior contact wash.
Second is to foam the exterior again. This provides more emulsifying power and lubricate the surface to protect from contact washing.
Now that the grime is suspended, we can safely remove it. We want a mechanically assisted removal process to help moving the emulsified dirt and grime from the surface. The mechanical process of the water hitting the surface assists with this.
Step three: Dump the left over liquid from the foamer into the wash bucket as the soap to wash the car with. That dilution should still foam when agitated. Add more soap if required. While the foam is still on the surface, we dunk the washing mitt or what you use to wash with in the bucket and then start washing the car, no pressure needed. It should just glide across the surface.
We are ready and appropriately prepared for washing the vehicle. Washing in this case implies contact washing. To further help removing the grime from the surface we need to agitate the oils and grime on the surface. This is because just the soap alone may not be able to break all the bonds between the particles and oils clinging to the surface. The pre-rinse removed most of the dangerous particles, so agitation with the soap on the surface is much safer. Softer brushes and Microfibre towels or mitts work best here.
After the contact wash, rinse. You have a choice to clean the openings like door jambs boot and bonnet areas now or later.