Deep Dive Into ph In Car Wash Soap

pH Car Wash Soap On A Porsche GT4

The latest addition of CarPro Reset to the store and my switch from Adam’s Car Shampoo to Koch Chemie GSF made me focus on the “why” of our car wash soap products. I want to understand how and why my soaps of choice perform the way they do. I thought it might be helpful for all of you guys to come along on this journey, especially considering all the buzz and marketing surrounding car wash shampoos. 

Setting the facts and essential information aside from the junk is difficult so I will do that for you. After all, that is one of the reasons we exist; to give you what matters and dump the other crap. 

The common sentiment within the car detailing industry is that you want a pH of 7 for your maintenance wash soap. However, this is not necessarily true. A soap with a pH of 9 can be gentler than a soap with a pH of 7. I have experienced this while searching for different soap products, examining Safety Data Sheets (SDS), and using them on my cars. This inherently becomes a dilemma for me. I spent most of my time searching for car soaps with a pH of 7 to ensure I kept my waxes and sealants intact for as long as possible. I now realize this thought process was flawed. 

As a result of re-racking my brain, I reached out to Dave at P&S Detailing Products to better understand how exactly pH affects detailing processes. I did this deep dive in 2019 when I decided to pH test car wash soaps myself. 

In summary, I pH-tested my maintenance soaps at the time: Meguiar’s Hyper Wash and Adam’s Car Shampoo, along with my decontamination soap. When testing, I was getting more alkalinity (pH above 7 to 14) with both Hyper Wash and the car shampoo when in solution (diluted) compared to their undiluted (out of the bottle) form. This made no sense to me, so I called Dave. 

During our phone conversation, we discussed several things that affect the pH of soap. I will make this as simple as possible for you, but it will be a tall task. There’s so much that can affect pH and cleaning ability that it’s hard to simplify it too much.

pH Higher In Solution Compared To Undiluted Soap - Why?  

The Adam’s soap initially tested at 7.26 pH undiluted, and the Meguiar’s was at 7.88 pH. However, the soap in solution (diluted to foam cannon concentration) was 7.8 and 8.05, respectively. For the initial test, I was using tap water with a pH of 7.6. How was my pH increasing to above both liquids’ pH levels? 

Dave was able to help make more sense of this for me. 

Strong Concentration and Equilibrium

They are in equilibrium when you have a weak acid or a weak base. The hydroxide ions are forced to stay put to the salt they are attached to upon blending the soap. When the soap got diluted out to the foam cannon dilution, these hydroxide ions were then freed to be measurable to show up on the pH meter’s reading because they were no longer in balance in the original solution of the undiluted soap. Even in this case, Dave said this isn’t a hard and fast rule. There are thousands of mechanisms of action for these products, and narrowing the chemical processes down to one simply isn’t possible. 

Chelation

In certain shampoos, there is an additive known as chelates. These chelates can change pH because they pull cations (positively charged ions) out of the water they are placed in, leaving anions (negatively charged ions) behind. This will increase pH, making the solution more basic. 

Chelation can also be a mechanism of decontamination in the car washing process. Depending on their concentration, chelates can pull away hardness minerals from your paint due to ion exchange. 

What Affects pH and Cleaning Ability in Modern Soaps?

With the VOC (volatile organic compounds) requirements from varying levels of government, manufacturers are forced to use different additives, such as non-ionic detergents and amphoteric surfactants. Additives like these replace more high VOC chemicals like glycol ether to increase the cleaning ability of soap. As a result, pH doesn’t tell the story about the cleaning ability of a detergent or soap as it did years ago, where more alkalinity or acidity meant more cleaning power. That’s not as true today as it was back then.

How Does This Affect How Soap Works?

The one takeaway from my call with Dave is that pH tells part of the story, but not all of it. Of course, a cleaner with a pH of 13 will strip waxes, sealants, or wear down your ceramic coating faster than a soap with a pH of 7. However, when discussing neutral-ish ranges, things get a little more interesting.

In our soap line, aside from rinseless wash (N-914 is about a pH of 8), we have three car soaps. Our decontamination soap has a pH of 10. The other two soaps I use are CarPro Reset and Koch Chemie GSF (pH-neutral maintenance soaps). Reset has a pH of 7, which is entirely neutral, and GSF has a pH of 7.5. This is about as close to “neutral-ish” as you can get without being a pH of 7. Nonetheless, Reset is probably 10-20% more aggressive than GSF. 

Intuitively, I would imagine that GSF would be slightly more aggressive. However, when I used Reset for the first time, I realized this wasn’t the case. But why does completely neutral car soap have more bite than a soap that is not entirely neutral?

Washing BMW E92 With pH Car Wash Shampoo 

Why pH Is A Misleading, Invalid Measure of Car Soap Performance

When it comes to car soap, dilution is usually high. We’re talking 128:1 usually as a maximum strength with most soaps, GSF is 200:1, and Reset is 500:1. These large dilution ratios mean that when the soap hits the bucket, you will see changes in pH without question. It’s part of diluting a product out that far. 

Additionally, when you make these dilutions at home, the minerals or level of hardness in your water will likely impact the pH enough to move it one or two numbers on the pH scale fairly easily. In other words, if your soap is a pH of 7, depending on your water, it would not be crazy for your soap to end up at a pH of 5-9 in solution in the bucket.

Don’t freak out. Manufacturers intend for this to happen. They expect you to use tap water in your wash bucket and foam cannon. This is how they plan we will use the product when they formulate the soap. If the soap is intended to strip, it will strip. If the soap is designed as a maintenance wash, it won’t strip waxes, sealants, or a drying aid. You heard that correctly; you can very well have a wash solution of 8 or 9 that will not touch your protective layer.  

If it isn’t performing the way the manufacturer advertised, the only way you will be able to know is by watching the performance of your protective layer, watching the foam out of your foam cannon, and how it mixes in the bucket. pH will not tell you JACK about performance. 

Takeaway

If I learned anything in this process, it was not to play “home chemist.” Detailing chemicals will perform to their intended use; if they don’t, the wash experience will tell you that they aren’t, not the soap’s pH. Dave made a point of prefacing our conversation with a bit of background on how he learned all of this stuff. 

pH is months and months of your studies in a chemistry degree, with every subject covering at least a few weeks of chemistry. It’s going to be challenging to understand the chemical processes as to how car soap functions in any reasonable amount of time, so just be observant of how the soap behaves and what it does to your car when you use it.