The 7 Most Common Misconceptions about Carpet Cleaning Chemistry – Part 6 – Acid Rinsing and Residue

Misconception #6 – Acid rinsing or fresh water rinsing leaves the least amount of residue in carpet after cleaning

What chemical solution do you run through your portable or truckmounted carpet extraction unit when you clean? The CRI SOA coined the term “In-tank” solution. Over the years, we have called these solution extraction detergents, rinses, and even souring agents. There are really four choices commonly applied these days:

1)      An alkaline powder or liquid carpet extraction detergent

2)      An acid neutralizing rinse. Some are detergent free and some contain detergent.

3)      Fresh water rinsing. Running nothing but tap water through your machine and rinsing the carpet with fresh water.

4)      Modified or energized water rinsing. Using some kind of electronic or ionizing treatment to modify the water to be more effective at soil removal and leaving less residue behind

Before you dig into this discussion, you may want to review our previous discussion of Misconception #5 – No residue, low residue. Good residue, bad residue. Our discussion here is going to concentrate on the idea that leaving the least possible residue behind is the goal of the carpet cleaning technician. Which rinsing or extraction method works best at achieving that goal?

Traditionally, dating back to the literal birth of hot water extraction, utilizing an alkaline powder or liquid carpet extraction detergent was the in-tank carpet cleaning solution of choice. In fact, the real old timers will tell you that carpet presprays are the new kid on the block, and that for many years the in-tank alkaline powder or liquid carpet extraction detergent was the only carpet cleaning chemical they used. Many cleaners started out utilizing these types of solutions and they remain their in-tank solution of choice.

After presprays became the most important part of carpet cleaning chemistry, other options for the in-tank solution sprang up. The idea of using fresh water only through your equipment was an easy concept to market from day one, especially if you went to the trouble and expense of installing a water softener on your carpet cleaning truck. Being from Colorado, the idea of the using “pure, fresh rocky mountain spring water” has been drilled into me by the local beer producer for years. It sounds logical that if you want to leave the least amount of residue, rinsing your prespray out with fresh water would work well.

The idea of ionizing or ozonating or electronically stimulating water to be more molecularly active and turn it into a better cleaning solution without the use of any other chemicals (last time I paid attention in chemistry class, H2O is made of chemicals) has proven to be a very effective marketing concept too. The less chemical you use, the less chemical residue you have to worry about seems to be a simple enough concept.

Acid rinsing has always been around in carpet cleaning. In the early days of hot water extraction, when so many carpets had jute backings which could easily develop cellulosic browning, a post cleaning topical spray with an acid anti-browning agent was often called for. That is where the term souring was used. Later, once again after presprays became the main carpet cleaning chemical, the idea of using an acid rinse was introduced for the purpose of preventing browning and chemical yellowing, and stabilizing colors and dyes. Then when stain resistant compatible chemistry was introduced (see our previous misconception discussion – Misconception #3 – You must use “Stain resist compatible” chemistry only on warranted carpets), there was a lot more focus on the pH of the cleaning solutions being used. Using an acid rinse or an acid detergent rinse to neutralize the alkaline residue left by the carpet prespray became very popular, particularly with trainers and chemical formulators who were promoting the use of a carpet prespray whose concentrated pH was above 10 (see our previous misconception discussion – Misconception #4 – Where is pH measured? Concentrated or ready-to-use pH), and they wanted to make sure the stain resistant carpet was left in a state where the residue did not have a pH higher than 10. Somehow out of the concept of pH neutralization, it was expanded to say that acid rinsing left the least amount of residue. The two concepts (pH neutralization of residue and leaving the least amount of residue) actually have very little, if nothing to do with each other.

Let’s start with what we do know.  First, there is no evidence that has been shown to me that alkaline, neutral, or acid residue left in the carpet are more or less likely to cause rapid re-soiling. The pH of the residue is not related to attracting soil or being sticky. Second, we need to operate on the same definition of what residue is. Residue is any matter foreign to the construction of the carpet. That includes soil (and all of its components – particulates, biological contaminants, and gas phase organics). It also includes any chemical or moisture we added to the carpet during the cleaning process that we do not extract out or that does not evaporate away. So if our claim and our goal are leaving the least amount of residue behind, then we measure total residue both in unextracted soil and cleaning solution left behind.

There are two ways that has been measured. The easiest for you to test yourself is by weight. Using a sensitive enough scale simply clean an area of carpet that has been accurately weighed before it has been exposed to any soil. Then uniformly apply soil and traffic it in. Weigh it again. Then clean the carpet with the system you think works the best. Completely allow the carpet to dry (if you want to be more scientific use a probe moisture meter and bring the carpet back to the exact same level it was before you added the soil or cleaned the carpet). The second measurement used by the Carpet and Rug Institute (CRI) in their Seal of Approval (SOA) program is by measuring particulates left behind after cleaning with an XRF analyzer. In their own words, here is how that works, “Since 2005, under The Carpet and Rug Institute’s Seal of Approval program, a new test to measure cleaning effectiveness has been used by applying the Keymaster’s XRF analyzer technology to carpets. Scientists from KeyMaster Technologies worked with Professional Testing Laboratory to design a special “soil” mixture that mimics actual soil found in carpet. The designer soil contains particles of five different types, each with a unique elemental composition. The range of particle types reflects the fact that soil composition differs in various parts of the country. Under carefully controlled conditions, laboratory testing staff use the XRF analyzer to measure the amount of soil in the carpet before and after cleaning with a vacuum or extractor. The test report presents the precise amounts and types of soil removed. The results from this new test are being used today to rate the performance of extraction machines. They provide important insights about the types and amounts of soil that are removed.” Now the purpose of this discussion is not to debate the relative merits or shortcomings of the CRI SOA testing. But here is what you can take away from this. First, XRF testing is not used in their evaluation of cleaning chemicals. It is used in their evaluation of cleaning systems. This is where side by side you can see how much of their lab soil was removed when comparing systems side by side. All four systems mentioned above are used in the system testing by various companies and franchises (alkaline, acid, fresh water, modified water). Note first, that all of the systems that earned Gold or Platinum status used a carpet prespray.

Having been a participant of many of the first kind of test (weight) and seen side by side actual measurements of the different systems tests (XRF), we can draw some conclusions about what “system” leaves the least amount of residue.

The answer is alkaline extraction detergent rinsing. Now before you get all hot and bothered, understand we are talking about minute, tiny differential measurements. All four systems properly applied do a fantastic job. What we were able to identify is that the amount of soil being removed is the biggest differentiator in the systems. Deep down imbedded, and stuck sticky soils in the bottom part of the carpet and primary backing are clearly the culprit. While a high quality prespray certainly starts the process of soil separation, emulsification, or dissolving, it is the flushing of the carpet with the alkaline detergent rinse that did the best job of removing that deeply imbedded soil and finishing the soil extraction. Properly formulated alkaline rinses, like HydraDri and HydraClean Carpet Extraction Detergent leave the least amount of total residue in a heavily soiled carpet. True fresh water rinsing leaves the highest amount of residue, likely because there is no cleaning power to remove the last traces of soiling deeply imbedded into the carpet.

Since the differences are so minute, we would rather have you marketing what you do well than worrying about which system is best. Just know the facts and benefits of your particular system, and don’t overstate the facts. All of the following three summaries below assume you used a high quality prespray on the carpet to begin with:

Alkaline Extraction Detergents like HydraDri, HydraFree DFC, HydraClean, and RinseFree with OxyBreak do the best job of cleaning, removing and extracting the most amount of soil and leaving the least amount of residue.

Acid Rinses, like ClearWater Rinse or RinseOut help prevent browning and chemical yellowing, stabilize colors, and perhaps most importantly to your customer leave the carpet softer to the feel and touch. For carpet cleaning, we recommend ClearWater Rinse because the detergency in it helps remove some of those last traces of deeply embedded soil.

If you are using a modified water rinse, you have likely already bought into a system which does a great job of describing the benefits of the system. Maximize those benefits in your marketing. Be careful about ozonating processes and claims there. There are several peer reviewed scientific studies which call into question whether the ozone really has time to treat the water when it is flowing at the solution flow rates of a truck mount. If you are using ionized or electronically altered water, the growth of your system or franchise speaks volumes about how consumers feel about the cleaning performance. Promote that.