The Importance of Chemical pH to Carpet Fiber and Stain Removal (For Newbies)

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Jason Whaley

Super Moderator & TMF Carpet Cleaning Specialist
Nov 13, 2008
Durham, North Carolina
Real Name
Jason Whaley
Business Location
United States
An important factor that affects the cleaning of stain-resistant 4th and 5th generation nylon carpets is the pH of the detergents or shampoos used in the cleaning process. Chemical pH may adversely affect the performance of the carpet, so it is important to understand the basics of pH as they pertain to carpet care.

In chemistry, pH is a quantitative scale for measuring the acidity or alkalinity of liquid solutions. The scale runs from the number 0 to 14. The number 7 on the pH scale is neutral, not acidic or basic. The number 0 on the pH scale is a strong acid; 14 is a strong alkali. So the pH scale runs from 0 (acid) to 14 (alkali).

On the pH scale each full number increase represents a tenfold increase of the acidity or alkalinity of the solution. It is a geometric progression by the number 10. So pH of 1 is 10 times more powerful than pH of 2. The pH of 2 is ten times more powerful than the pH of 3 and 100 times more powerful than pH of 4.

The numbers on the scale denote the "strength" characteristics of the solution not the "quantity" or dilution of the solution. Whether you have a drum of lye or a tablespoon of lye they both have the same strength characteristics (pH).

In order to prevent damage to carpet, the carpet cleaner should leave the carpet as close to 7 on the pH scale as possible. The manufacturers of all stain-resistant and 4th or 5th generation nylon carpets require a cleaning solution with a pH of 10 or below.

If a chemical with a higher pH than 10 is used, it will void the guarantee of these carpets from the manufacturer. Highly alkaline detergents and shampoos will also damage wool carpet. On other types of carpet, a pH of 12 is the maximum that should ever be used.

Carpet pile fibers are dyed in acids with a pH of 2. That is why highly alkaline cleaners may cause alkaline browning of light pile fibers.

Stain Removal

All stains are either water-soluble or solvent-soluble. Solvent-soluble stains require solvents to redissolve the stain and release it from the carpet. Water-soluble stains are neutralized using alkaline and acid based spotting agents. Stains are neutralized by using a spotting agent of the opposite pH value of the stain.

Neutralize acid stains by using an alkaline spotting agent.

Neutralize alkaline stains by using an acid spotting agent.

Some stains have no pH because they are waterless stains. You must use a neutral product (solvent) to remove these stains.

Acid spotting agents work very quickly.

Alkaline spotting agents take a minute or so to work.

Jarrod E

New Member
Aug 14, 2009
Real Name
Jarrod Elliott
Business Location
very nice Jason, this should be made sticky.

Scott W

Preferred Vendor
Premium VIP
Feb 14, 2006
West Jordan, UT
Some good basic information on pH. However, it is important not to be overly focused on pH alone. There is much more to the whole picture - total alkalinity, buffering and reactivity.

For example, a product may have a pH of 10.5 When you dilute it with water (which has a pH of 7) what is the new pH? It could be anywhere from 10.5 to 7 depending on total alkalinity. Some products drop in pH when mixed with water. Others don't.

What about the pH of a product as it reacts witht he soil in the carpet? Some products lose pH as they react with soils. Other maintain the pH and so keep working longer. This is the result of buffering.

When cleaning wool rugs that can be sensitive to acids, there use to be a "rule" that said keep the pH between 5.0 and 8.5) However, testing has shown that some products with a pH of 11 can be used on wool becuase they lose their pH rapidly when diluted and in contact with soil. Others with a pH of 7.5 could cause damage because they never did loose their slightly alkaline pH.

Look for an article I wrote for Cleanfax a couple years ago or information Iposted in the chemistry section if you want more on this topic.