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The science of carpet and upholstery cleaning

October 11, 2010
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The first step in proper carpet and upholstery cleaning is to educate yourself. You just know what type of fabric or carpet materials you are working with. Don’t guess; do your homework. Find out from manufacturers what materials they are using in their vehicles. In most cases the carpets are nylon, but the upholstery can be any number of synthetic fabrics you need to familiarize yourself with.

Second, you must identify the problem, or problems. That is, the type of dirt or stain(s) that has to be removed and to what extent you can remove them.

About 85 percent of the soil in carpets/upholstery is dry. The other 15 percent is oily soil on the fibers of the carpet/upholstery. Then there are the stains. Stains will typically be related to:

  • Food;
  • Grease;
  • Red dyes;
  • Coffee and tea (tannins);
  • Rust; and
  • Pet waste.

The next step after identifying the type of carpet/upholstery as well as the soil or stain is to evaluate and choose the best cleaning method.

Cleaning procedures
There are two types of cleaning methods: Friction and non-friction. Friction cleaning involves hand or rotary scrubbing, while non-friction cleaning depends upon extraction or vapor steam cleaning tools.

In the case of non-friction methods, the dirt is removed by the action of the chemical being injected into the fabric under pressure while simultaneously vacuuming the area. It can also be liquefied by hot steam and then removed by vacuum or extraction.

The following procedures are those recommended by the Carpet Cleaning Institute:

1. To remove the dry soil, give a very thorough vacuuming and use a vacuum with good suction. Use thoughtful and thorough vacuuming to remove as much of the dry soil as possible before introducing moisture into the fibers.

2. Next, analyze any stains that are on the carpet/upholstery and the application of the appropriate stain removers. (See side bar on Removing stains)

3. To remove the oily soil, a carpet/upholstery shampoo and spray it lightly over the entire area to emulsify the oily soil.

4. Next, use a friction shampoo with a scrub brush or better yet, a rotary shampoo tool.

5. Then, using a heated soil extractor rinse clean the shampoo and oily soil residue from the carpets and upholstery.

6. A final vacuum will then aid in removing any residue moisture.

A hypothetical example
Let us take a hypothetical interior that has plush carpets and velour upholstery. The carpets have grease stains as well as coffee and what appears to be gum. There is also a heavy concentration of ground-in sand. The upholstery is in unusually good condition considering the condition of the carpets.

The first step would be to use an air gun to blow all dirt and grit out of the cracks, crevices, seams, etc. Next, thoroughly vacuum the entire interior utilizing both a snorkel nozzle and the long slender crevice nozzle to get to those hard to reach places between seats, etc. Utilizing the appropriate stain remover chemicals apply to all spots on carpets, upholstery and door panels.

For chemicals to work effectively they must have time to dwell. This is especially true with stain removers which need to dwell for several minutes, and then be agitated with a hand brush. Be sure to move inward toward the center of the spot rather than outward which can spread the stain.

Certain stains should be blotted rather than scrubbed. This process could require two or three spotting applications. Gum can be removed by using an appropriate remover or hardening it with ice and using a putty knife or scraper.

After removing the spots, you are ready to shampoo the carpets and upholstery. A vapor steamer is an invaluable tool to quickly and effectively remove stains.

Cleaning carpets
The kind of process you use (rotary/hand scrubbing versus extracting/vapor steaming) depends on the types of soil and stains to be removed. Shampoos designed for scrubbing have foaming agents. When agitated by the hand or rotary brush the foam encapsulates the dirt particles and lifts them to the surface where they can be easily extracted and vacuumed up.

In our hypothetical case, we have a carpet with a lot of ground-in dirt. In my experience, a good way to remove ground-in dirt is as follows:

1. After thoroughly vacuuming, spray the area with shampoo, allow dwelling for a few minutes, and then aggressively scrub with a hand brush or rotary shampooer. After you have created a lot of dirty foam, use the heated extractor to rinse and vacuum.

2. Depending on how dirty the carpet is you may have to repeat the process two or three times to “drag out” all of the dirt. The only other way is to remove the seats and the carpet shell and pressure wash the dirt out and then shampoo.

3. Be mindful of the condition of the carpet after you have cleaned. High foam shampoo can leave a residue even after you have used the extractor. This will make the carpet fibers sticky and attract new dirt.

Instead, you must thoroughly rinse the carpet fibers of all residues to avoid what is called resoiling. Carefully inspect your work after you have rinsed to make sure you do not need to rinse again.

4. For carpets that are moderately dirty you can vacuum and spray with shampoo and scrub with a hand brush or rotary shampooer and then use the extractor to rinse.

5. In the case of surface dirt the extractor can be used as the sole cleaning method if the carpet is not too dirty. One problem with the extractor is that the nozzles are sometimes too large to reach all areas so you do need to hand scrub and then use a crevice tool to vacuum up the residue.

Cleaning upholstery
Upholstery fabrics (excluding vinyl and leather) are far more varied than carpets and while they all seem to clean the same, they are different. Dismissing these differences in fabrics would be like dismissing the differences between base-coat/clear-coat and single stage paint finishes.

In cleaning upholstery, you will apply the same logic as with carpets. Identify the fabric, identify the cleaning problems, choose the proper chemicals, and select the best cleaning methods. As with carpets, you will have to spot stains based on the type whether grease, protein, etc. Then after evaluating the extent of the dirt decide whether to use the scrubbing method, vapor steamer, extraction, or a combination of all.

With velours, whether heavily soiled or not, I recommend a light shampoo, moderate scrubbing and extraction. For some with only surface dirt the extraction will work. With some fabrics, like tightly woven tweed that is extremely dirty, you may have to spray shampoo, aggressively scrub and then extract.

Never give up
One last thought I will leave you with is that you should not give up too easily when confronted with really dirty carpets or upholstery. Once is not enough in most cases, especially with ground-in dirt.

If you understand the differences between chemicals and have available all the cleaning tools and methods you can clean almost any dirty interior.

R.L. “Bud” Abraham is president of Detail Plus Car Appearance Systems, Portland, OR, and a nearly 40-year member of the car care industry. He is also the executive director of the International Detailing Association and a member of the Western Carwash Association Board of Directors. Abraham can be contacted at