Conventional methods for cleaning and sanitizing commercial grouted ceramic tile floors involve applying aqueous solutions to floors with repeated wetting and wringing cycles using mops and two- or three-compartment buckets. In contrast, in the spray-and-vac method, fresh cleaning and sanitizing solution is applied to the floor with a spray gun and subsequently extracted by vacuum into a waste containerbuilt into the machine. For removing bacterial contamination, the data shows that the spray-and-vac machine is 60 times more effective in reducing bacterial contamination than the conventional method for typical commercial floors, such as those used for aseptic processing.

Removal of microbial contamination from ceramic tiles and especially grouting presents a serious cleaning problem because of two factors. Grouting is softer and more porous than tiling and the surface of grouting, and the “grout line” is most often lower than the surfaces of the tiles. Also, the construction of floors with small tiles — common in modern buildings — results in high ratios of grouting surface areas to tile surface areas. Thus, successful removal of microbial contamination of floors by cleaning operations dependscritically on removal of the contamination from grouting.

Numerous scientific methods are available to determine quantitatively surface cleanability and cleanliness. In practical situations, the quantitative cleaning and assay methods selected are based on the cleanliness level required, on the type of surface material and on the type of soil.1,2Although cleaning standards for ceramic tiles have been established (ASTM D5343, 2006), the standards specifically exclude application to the grouting between tiles.

Jointing grouts are usually made of cement, epoxy, a mixture of cement and epoxy, or of an elastic grout material, such as silicone, uretan, or acryl. Only a limited number of investigations have been published concerning the qualitative cleanability of ceramic or any other tile grout materials. In particular, the significance of the porosity and roughness of conventional grout lines is not well known with respect to their cleanability. Recently the cleanability of grout has been studied quantitatively.3This study compared the cleanabilities of cementitious grout, mineral polymer covered cementitious grout, and epoxy grout, and concluded that epoxy grout was the most easily cleaned of these grouts. This finding is expected, since epoxy was the hardest and the least porous material of the grout materials included.

With respect to removing bacteria from porous and rough surfaces, Holah and Thorpe4studied bacterial retention on various ceramic materials. They suggested that the greater the degree of surface irregularities, the greater the chance of bacterial retention after cleaning. The roughness of the surface also increased the area to which bacteria were able to fasten.

For determinations of microbial contamination on solid surfaces, including ceramics, recommended methods have been developed to allow quantitative determination of bacterial and viral removal (ASTM E2414-05; AOAC 961.02). Standard guidances for analyzing microbial contamination of grouting have not been developed.

In this article, we present quantitative data on removal of dried deposits and microbials from soiled tiles and bacterial removal from the grout line using protocols based on standard analytical microbiological practices for examining residual bacterial contamination on surfaces.

A mild, multipurpose, pH neutral, cleaner that combines citrus d-limonene with hydrogen peroxide was used at a dilution of 2 oz/gal in tap water for cleaning tests using this agent.
A hospital grade broad spectrum, pH neutral disinfectant was used at a dilution of 2 oz/gal in tap water for cleaning tests using this agent.
Household Bleach was used at a concentration of 200 ppm.

Mop Cleaning Method
The following mop cleaning procedures were used throughout this investigation:

  • Fresh tap water and a fresh, never-used, mop head was used for each cleaning application.
  • The mops were thoroughly wetted and wrung out in a mop-bucket wringer resulting in a dampened mop.

The test area was then cleaned by making a first pass of the mop across the area and then making a second pass in the opposite direction. For each pass across the floor, a slight downward pressure was applied to the mop via the mop handle.

High Flow Fluid Extraction (“Spray-and-Vac”) Cleaning Method
The following standard spray-and-vac cleaning process was used in this investigation:

The cleaning machine used consisted of an indoor pressure washer (500 psi) with low and high pressure settings for applying solution and rinsing, automated chemical dilution/injection system, fresh water tank (15 gallons), wet vacuum (110 inches of water lift) system for high flow fluid extraction, and vacuum tank for isolating and containing soils.

First, the test area was irrigated/flooded with the cleaning solution from the spray gun of the cleaning machine with the nozzle in the low pressure mode.

The cleaning solution was allowed to dwell on the floor for five minutes.

The solution was then removed from the floor via high flow fluid extraction using the vacuum tool and squeegee assembly. A first pass was made across the area and then a second pass was made in the opposite direction.

A quantitative comparison of effectiveness of mopping and spray-and-vac cleaning of a floor was performed. The floor was sectioned off into test areas — one area for each of the two cleaning methods being evaluated. Each area was identical in size, and included two grout line intersections. In addition, each area was remote, so that there would be no flow of liquids or solutions from one area to another.

The test areas were cleaned using a designated cleaning method — mop cleaning and spray-and-vac cleaning as previously described. For these initial tests, cleaning chemicals were not used.

After cleaning, contamination of the grout line intersections and surfaces of the ceramic tiles was measured. At the grout line intersection, measurements were taken in all four directions to capture data in parallel and perpendicular to the cleaning direction.

Comparison measurements of viable bacterial counts remaining after two different cleaning methods were made between mop cleaning and spray-and-vac cleaningon grouted surfaces of a floor.

These tests were performed using a grouted ceramic-tile floor. Each floor was sectioned off into test areas. The first section had test areas for spray-and-vac cleaning including brushing. The second had test areas for flat mop cleaning.

Four different grout lines were measured for each section of floor. Contamination was measured and samples were taken from a square inch of grout line area.

The test areas were cleaned using the corresponding cleaning methods previously described. In addition, the spray-and-vac test areas were brushed during the dwell time, with a firm-bristled brush using a two-pass back-and-forth motion.

Ten minutes after the test areas had been cleaned and dried, bacterial samples were obtained. The data was recorded and measurements made in quadruplicate. Statistical analysis was done as previously described.

Figure 1 shows the fraction of CFU (colony forming units) per square inch of grout line areas normalized to the CFU count for the same uncleaned areas. The measurements were taken at the grout lines of the floors before and after cleaning using only water. The mop removed about 50% of the initial bacterialcounts while the spray-and-vac machine removed almost 90%.

Figures 2 and 3 compare the fractions of bacterial counts left after grout line cleaning with a multipurpose cleaner and a hospital grade disinfectant, respectively added to the cleaning solutions used with mops and the spray-and-vac machine. These results reveal that mop cleaning with the disinfectant is slightly more effective than mop cleaning with the household cleaner. But in both cases, almost half of the original bacterial counts were still present. On the other hand, with both cleaners as additives, the spray-and-vac machine left only a small fraction of bacterial counts at the grout line: 1% and 0.8%, respectively.Thus, with additives, the spray-and-vac machine is roughly 60 times more efficientthan mopping in removing bacteria from the grout line.

The data show that for ceramic tile floors, the grout line presents a more difficult surface for removing dried contaminants and bacteria compared to the flat, ceramic tile surface. Mop cleaning was approximately twice as effective at cleaning the tile surface compared with the grout line (76% and 74% cleaning efficiency compared to 38% on the grout line). However, spray-and-vac cleaning did not have this same difficulty demonstrating a cleaning efficiency for both tile and grout surfaces at 98%.

We believe that the reasons for these results are as follows. The mop fibers appeared to have difficulty making contact with the grouted surfaces due to the concave shape of the grout line. Secondly, the grout line is difficult to clean due to the higher surface roughness compared with the smooth tile surface. This higher surface roughness results in surface irregularities where dirt soils get trapped and become difficult to remove. When evaluating the effectiveness of a cleaning method for a tiled surface with grout lines, it is very important to measure the grouted surfaces to ensure accurate evaluation. It is very probable that inadequate cleaning of the grout lines of floors using convention al mop methods is the cause of contamination causing high bacteria growth and dispersion of bacteria to other areas.

The data presented here shows that spray-and-vac clean ing is by far the most effective cleaning method removing contamination from a ceramic tile and grouted floor. At the grout line after cleaning with water, mops left 30 times more soil than spray-and-vac cleaning even with a new mop used for cleaning. This equates to cleaning efficiency of 38% for mop cleaning compared to 98% for spray-and-vac cleaning. On tile surfaces after cleaning with water, mops left 12–13 times more con taminants than spray-and-vac cleaning. This equates to cleaning efficiency of 76% for mop cleaning and 98% spray-and-vaccleaning.

It may be theoretically possible to achieve cleaning and bacterial removal efficiencies at the spray-and-vac levels with traditional or microfiber mops. But, based our findings, this would be possible only by supple menting those methods with more aggressive agitation, as with a brush, longer dwell time for the cleaning solu tion, or an increased duration of mopping and rinsing All of these changes would have a great impact on the cleaning productivity.

Anecdotal information is not sufficient for validating cleaning methods and accurately quantifying cleaning effectiveness. It is important for cleaning industries pursue science in order to educate communities on the importance of cleaning and its impact on health. In doing so, understanding the sciences and technologies of clean ing and disinfection is critical.


  1. Chawla, M.K., How clean is clean? Measuring surface cleanliness and defining acceptable levels of cleanliness, in Handbook for Critical Cleaning, B. Kanegsberg and E. Kanegsberg, Editors. 2001, CRC Press LLC. p. 415-430.
  2. Chawla, M.K., Monitoring cleanliness and defining acceptable cleanliness levels, in Surface Contamination and Cleaning, K.L. Mittal, Editor. 2003, VSP BV: The Netherlands. p. 23-41.
  3. Kemppainen, M., et al., Cleanability of ceramic tile grout materials. Ten-side Surfactants Detergents, 2002. 39(1): p. 8-12.
  4. Holah, J.T. and R.H. Thorpe, Cleanability in relation to bacterial retention on unused and abraded domestic sink materials. J Appl Bacteriol, 1990. 69(4): p. 599-608.

*Additional details on the study can be obtained from the author.

Jay Glasel, Ph.D., is the founder of Global Scientific Consulting, LLC, located in Farmington, CT. Global Scientific provides a wide range of scientific consulting, writing, and training services in areas of the physical, chemical, and biological sciences. Global Scientific may be reached at 860-677-7913;