Antimicrobial Sealers and Cleaners

   Now you’re seeing specialty-care products, such as those for natural stone, using these terms on their labels. What does this mean for our industry and why is – or isn’t – it important?
   Consumers are beginning to ask questions about the proper care of granite countertops. They want to know the answers to the most-basic questions, from the need to seal granite or other stones to the best cleaning products to use. You even have consumers asking about the possible microbial contamination of their granite countertops.
   What has the stone industry done to address these concerns? Do you have the answers when your customer asks about the need to seal? What cleaners are you recommending? This brief overview of stone care and antimicrobial products is designed to give you some answers to these questions, so that you can better inform your customer.
  
Countertop contamination – what’s been done
   In March 1999, for example, the Hospitality Institute of Technology and Management published an article on The Reduction of E. Coli on Various Countertop Surfaces¹. The study looked at six surfaces (laminate, wood, tile (ceramic), concrete, stainless steel and granite) and their cleanability.
   All of the surfaces were contaminated with a measured quantity of E. Coli culture, cleaned with a detergent solution, rinsed, and tested to determine the reduction of the bacteria. The surfaces were then cleaned using a solution of white household vinegar, and tested again to determine cleaning effectiveness.
   The study results showed, as expected, that every countertop has a different cleanability. In addition, the granite showed the greatest reduction of bacterial contamination after the wash-and-rinse step, while the stainless steel had the greatest reduction after the vinegar-sanitizing step. What is of particular interest to our industry, however, is that the “most-cleanable” materials were stainless steel and granite.
   At StoneTech Professional’s 2000 Symposium, we presented an in-house study on The Effects of Sealing and Cleaning on the Biocontamination of Natural Stone². Two types of stones were tested: polished Kashmir White granite and honed Euro Beige limestone. Both sealed and unsealed samples of these materials were treated with a measured quantity of a mixture of contaminants.
   This mixture was a combination of chicken liver “blood,” liquid from a piece of beef tripe, grapefruit juice, whole milk well past its expiration date and Roquefort cheese. These samples were allowed to sit in a warm humid environment for two days. Contamination levels were measured using a bioluminescence hygiene monitoring system, similar to those used to measure cleanliness in dairy and other food-processing plants.
   When compared to uncontaminated stone (using unsealed and sealed controls), the rate of growth of contaminants for the limestone was 7,700-percent-more on unsealed stone and 4,400-percent-more on sealed stone. This was also consistent with the results on the granite, which were 18,000-percent-more on unsealed stone and 9,000-percent-more on sealed stone.
   What was also interesting was that cleaning the stone with a cleaner specifically formulated for stone dropped the limestone contamination by more that 750 percent on unsealed stone and more that 1,250 percent on the sealed stone. The reduction on the sealed stone brought the contamination level low enough to be considered “clean” in most food processing environments.
   Similar results were found on the granite, with an interesting twist: When the sealed granite was cleaned with plain, distilled water, the contaminant level was also low enough to be considered “clean” in most food-processing environments.
   Another consistency with all of the samples was that when the unsealed stones were cleaned with the cleaner – or with water – their contamination levels never got as low as the cleaned sealed samples. It’s a good indication that the contaminants may have had an opportunity to grow into the pore structure of the stone and not sit on the face and be wiped off easily.
   Porosity of natural stone is a characteristic that we cannot eliminate or change; it exists to some degree in all natural stone³. We can lessen its negative effect on cleanability, however, by keeping contaminants from getting into those pores in the first place, by proper sealing.
   Two key conclusions that came from that study were that:
   1. Sealed stone had less bacterial growth than unsealed stone;  and
   2. Sealed stone was able to be “cleaned” more than unsealed stone.
   But, what could an antimicrobial agent do?
  
Antimicrobial sealers and cleaners – present day
   Look at the products available to today’s consumer and you’ll see the words antimicrobial and antibacterial on many cleaners. Products that are truly antimicrobial cleaners (antibacterial is actually a subcategory of antimicrobial) must meet strict requirements for performance set by the U.S. Environmental Protection Agency (EPA) and must be registered.
   But what about antimicrobial claims that you see on products like paint, cutting boards and toys? How can these products, that are not cleaners, be antimicrobial? Upon closer inspection of these products’ labels, you’ll see that they often make claims like “…this paint contains a preservative that inhibits the growth of mildew on the surface of this paint film…”
   These claims are legitimate and fall under a provision of the EPA regulations called the treated articles exemption. This exemption allows the incorporation of antimicrobial agents into materials such as paint, plastics, coatings and other polymeric materials that will inhibit the growth of bacteria, mold, mildew, yeast and fungus on the surface of such products.
   In the case of a stone sealer, the sealer that remains in and on the stone can have antimicrobial product protection. This means that the sealer is treated with an antimicrobial agent to inhibit the growth of microbes (e.g., fungi, mold, mildew) on the cured sealer. The antimicrobials are built directly into the formula for a very effective system that cannot wash or wear off like soaps or disinfectants.
   If a high-performance sealer is working effectively, there shouldn’t be any moisture penetration into the stone. This reduces the likelihood of microbial growth, since most bacteria and fungi need moisture and a food source to grow. If this same sealer is treated with antimicrobial product protection, then the sealer coming in contact with contaminants on the stone’s surface will not support bacterial or fungal growth.
   But common sense (and previous studies) dictates that we have to clean up spills and other surface contaminations. How do we best clean natural stone?
   There is a wide array of cleaners on the market, but only some that are specifically formulated for natural stone. Within this group, there are also disinfectant and antimicrobial cleaners, but are these the best to use with today’s high-performance sealers?
   Traditional disinfecting or antimicrobial cleaners, even though they may be safe to use on stone, may not be the best option to use in conjunction with a high-performance sealer. Common residual antimicrobial agents used in these types of cleaners are quaternary ammonium compounds that, although recognized as effective residual antimicrobials, are also hydrophilic (water-loving) – they’re likely to attract water-borne soils and stains to the stone. Common disinfecting agents, such as hypochlorite-based solutions (think household bleach) can quickly degrade a high-performance sealer within a few uses.
   If the sealer used on a stone contains antimicrobial product protection, however, it makes sense that the best way to clean the stone would be with a product that will remove surface soils, but keep the sealer intact. When choosing or recommending maintenance cleaner for a sealed stone, make sure that the cleaner you’ve selected is not going to damage the high-performance sealer. Some cleaners may even have the added benefit of leaving behind more of the sealer with antimicrobial product protection that you originally specified.
  
Conclusion
   Technology in the stone-sealing industry keeps evolving with new generations of high-performance sealers on the market today, so it’s important to choose carefully. Which of these are the best for your customer’s stone investment? Do you need the antimicrobial protection that some products offer? Would your customer benefit from not having mold, mildew or other fungi grow on the sealer in the stone?
   And, once you’ve sealed a stone, make sure that you recommend a cleaner that works with the sealer you applied and not against it, which would degrade or damage its performance. Manufacturers usually know which of their products are designed to best work with their products.
   Many manufacturers have developed their sealers and cleaners to work in a complementary manner – a systematic approach to stone care. Ask your supplier or contact a stone-care-products manufacturer for more information.
  
   Michael N. Guasch is president and chief technical officer of StoneTech Professional Inc. in Walnut Creek, Calif.
  
   ¹ Snyder, O. P., 1999, The Reduction of E. Coli on Various Countertop Surfaces, Hospitality Institute of Technology and Management, Mar. 22,1999.
   ² Ramirez, C.L., 2000, The Effects of Sealing and Cleaning on the Biocontamination of Natural Stone, June 2000.
   ³ Guasch, M.N. and Lessard, P.C, “Structural and Chemical Effects on Water Absorption,” Stone World Vol. 19, No.11:58-67.

This article first appeared in the February 2004 print edition of Stone Business.