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Deeper Details of Disinfecting

From an article in CLEANFAX digital magazine

By Mike Kerner


September 04, 2014

We know that disinfectants are important items in the cleaning and restoration professional toolbox, but how do we make sure we’re using them safely and to their maximum advantage?

I hear these questions time and again, so let’s look at some important facts about disinfecting:

Always follow label instructions

This mantra has been in our industry for a very long time and for several good reasons:

  • It’s the law! The label of an EPA registered product is a legal document and must be followed exactly. Businesses that do not follow label directions are liable for fines.
  • Dilutions are important: As you well know, if you use too high a concentration, you risk leaving behind residues and wasting money. Use too little and you risk accomplishing nothing, also wasting time, product and money.
  • Mixing with other products: This is a significant yet poorly recognized risk. Disinfectant actives can be neutralized by ingredients commonly found in cleaning products. A common example is mixing a general purpose cleaner that contains an anionic (negatively charged) surfactant with a quaternary-based (positively charged) disinfectant. These components will neutralize each other, and in all probability the resulting mixture will neither clean nor disinfect properly. Another example is mixing products with different pH levels. Altering the pH this way can harm the efficiency of some disinfectant products.

Clean before disinfecting

Usually described as “precleaning,” this might seem counterintuitive. If a product is promoted as a “detergent-plus-disinfectant,” but the label says apply to a “precleaned” surface, what on earth is the detergent for?

To some extent, whether to preclean is a judgment call. Disinfectants can work in the presence of limited amounts of organic soil. But if the soil load is too great, the soils will inhibit the disinfectant’s ability to kill bacteria. On the other hand, if the soil load is light, then a detergent-plus-disinfectant application might be adequate. You have to judge the soil load to determine which approach is appropriate.

Another good reason for precleaning is the existence of biofilms. Biofilms have received much attention over the past few years. Microbiologists have learned that bacteria can form tightly knit communities that layer themselves over surfaces in thin, self-protective mats or films.

In many cases, “spray on, wipe off” will not be sufficient to tackle biofilms. It takes good old fashioned elbow grease and rigorous agitation to release them. Adequate precleaning will dislodge and disrupt these clingy bacterial films.

Proper amounts, proper dwell time

Disinfectants require direct physical contact with the germs they are intended to kill. They also need time. This means you need to apply enough ready-to-use solution to wet the surfaces and be sure surfaces remain wet for the label-mandated contact time.

Sadly, the amount of solution that must be applied for a certain contact time is hard to predict; there are simply too many variables. The variables include the moisture content of the air and air circulation — both of which affect evaporation rates — as well as the texture, porosity and chemical properties of the surface.

For example, a hard plastic counter top sprayed in Minnesota in the middle of winter will dry very quickly, while wallboard sprayed in Louisiana in August will probably never dry. This is a bit of an exaggeration but you get the point.

The best approach is to apply product in a given situation, note the drying rate and reapply as needed.

A 10 minute contact time is believed by many the universal standard. But it’s worth mentioning that some labels show times as short as 30 seconds. Note that contact times usually refer to specific organisms, so unless you know that the surface you are trying to decontaminate has that specific bacteria and only that specific bacteria, you need to follow the longer recommended contact times.


One final note: People often speak of “killing” fungi, bacteria and viruses. It is correct to say “kill” for fungi and bacteria because they are living organisms; they respirate, metabolize food sources and reproduce. Antimicrobials interrupt one or more of these processes to kill the organism.

Viruses are a different story. Instead of respirating and metabolizing food, a virus makes more viruses by hijacking the reproductive mechanism of a living organism. Antimicrobials stop viruses by damaging the outer shell of the virus so that the hijacking mechanism no longer works. So it is more accurate to say we deactivate viruses.

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