Biocide Selection: In-can Preservation, Dry Film Protection, Anti-fouling...

Interior coatings used especially in kitchen and bathrooms are more vulnerable to microbial degradation due to damp conditions. And for exterior paints, environmental conditions like humidity can lead to fungal/ algal growth and negatively affect the aesthetics of the coating. Apart from architectural segment, microbial issues are also predominant in the marine industry leading to problems such as high maintenance costs, increased corrosion etc.

Also, not only limited to after use spoilage, microorganisms can contaminate the paint in different ways during the manufacturing process too.

Are you hunting for the right biocide for your coating formulation? Does the ever-changing global regulatory landscape for anti-microbial additives make the selection process daunting for you?

Understand, in detail, what to consider while selecting the right biocide or anti-foulant for your paints and coatings. Check out:

  » Reasons of microbial growth in coatings
  » Main types of biocides used in paints & coatings
  » Selection Criteria to find best suitable biocide system for your product (coating type, application, regulations etc.)
  » When should you consider blends?

We would like to acknowledge Marc Hirsch for providing technical information needed to develop this guide.

Need for Antimicrobials, Types & Selection Tips

TAGS:  Architectural Coatings     Marine and Protective Coatings      Biocides/ Antimicrobial Agents    

Biocide Selection: In-can Preservation, Dry Film Protection, Anti-fouling...At every stage of their service lives, paints and coatings are susceptible to contamination and degradation by a variety of microorganisms. Further, the presence of water makes these paints very susceptible to microbial attack - both in the wet state and as dry film.

  • Bacteria can spoil emulsions and paint in the storage container
  • After paint has been applied to a substrate and dried, it becomes vulnerable to attack by the fungi that cause mildew 

To protect against the microorganisms that can cause problems, paint manufacturers must customarily use biocides.

What is biocide? Antimicrobial additives (also called Biocides) are used in formulations to keep bacteria from spoiling paint during storage, or to keep fungi, algae and other micro-organisms from growing on the applied paint.

What is biocide used for? The two main applications of biocides are:

  • In-can protection to prevent spoilage of the wet-state product during storage and transportation
  • Dry-film protection to ensure long-term performance of the coating

» View All Commercially Available Biocides/Antimicrobial Agents & Suppliers in Coatings Database

This coatings database is available to all, free of charge. You can filter down your options by suitable resin, system or application (coatings, inks...), supplier and regional availability.

Microbial Growth in Coatings - Why and How?

Microbial growth in the wet state is usually manifested by a loss of product functionality and may include gas formation, offensive odors and changes in pH, viscosity and color. Microbial contaminants can be introduced:

  • With water (process water, wash water), 
  • With raw materials (latex, fillers, pigments, etc.) and 
  • By poor plant hygiene

Bacteria are the most common spoilage organisms, but fungi and yeasts are sometimes responsible for product deterioration. Spoilage of the waterborne products, which may go unnoticed until the product reaches the consumer, can result in significant economic loss.

Upon drying, both water- and solventborne coatings are susceptible to colonization by fungi and/or algae.

Effect on microorganism growth on dry-film

  • Fungi can penetrate coatings, resulting in cracking, blistering and loss of adhesion, leading to decay or corrosion of the underlying substrate. 
  • Algae colonies, which seem to grow more rapidly on porous substrates such as stucco, cement and bricks, can occlude water. 

The freezing and thawing of this entrapped water may induce cracking or increase the permeation properties of the coating, leading to failure

The presence of water may also encourage colonization by other microorganisms, which in turn may cause bio-deterioration.

The type of microorganism that can colonize the coating will depend on several factors, including:

Preserve Products
in the Can as well as
After Application
Prevent Coatings from Degradation Thanks to Biocides
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Lonza's Range of Biocides
for Paints & Coatings
  • Moisture content of the surface - Surface moisture content is affected by climatic conditions (amount of rainfall, dew, humidity, temperature and time of the year) as well as by local conditions (surfaces sheltered from winds and shaded areas will contain higher moisture content)
  • Presence of nutrients - Nutrient sources include constituents of the coating itself (such as polymers, thickeners, etc.), partially biodegraded substances produced by other microorganisms, or simply material deposited on the coating from the atmosphere, such as dirt
  • Substrate - The composition of the substrate may affect the pH of the surface, making it suitable for microbe colonization. For example, fungi favor more acidic conditions, such as those provided by wood. Some species of wood are more susceptible to colonization by fungi than others (e.g., pine is more susceptible than cedar). Algae, on the other hand, favor alkaline conditions, such as those provided by masonry.
  • Coating composition - the coating composition and properties (polymer type, water repellency, porosity, hardness, chalking and roughness) determine the type of microbial community that will colonize the coating

The use of biocides is recommended to maintain the microbiological quality of a product and to protect it against contamination 

There exists a criterion for selecting antimicrobial additives depending on the coating type and end-use application of your product. To learn the same, it is important to know about the types of antimicrobial additives available in the market, their chemistries and purpose of addition.

So, let's move on to discuss types of biocides available for paints & coatings...

Main Types of Biocides Used in Paints & Coatings

In-Can Preservatives

All waterborne paints contain nutrients for bacteria, fungi and yeast.  Microbial attack can therefor happen inside the can, which would affect the quality of the paint. When it happens, you can experience:

In-Can Preservatives for Paints and Coatings
  • Foul odor
  • Loss of viscosity
  • Gassing
  • Phase separation
  • Discoloration
  • pH drop

To protect your coating from such issues & extend the storage life of your coating, you have to use In-can Preservatives. They are organic materials. They are used at low levels; < 0.1% by weight typically.

An efficient In-can biocide should have the following properties:

  • A broad-spectrum antimicrobial efficacy
    Measurement of Minimum Inhibitory Concentration (MIC) is a good way to test biocide efficacy. MIC is the lowest preservative concentration at which growth of a test organism is inhibited under laboratory conditions.

  • Long-term protection
    Paints may be kept in storage for long periods and exposed to wide temperature variations. Optimum preservation can only be achieved if the in-can preservative is compatible with coating ingredients and is stable over time.

 » Check Out All available In-can Preservatives Available in the Market Today!

Anti-Fouling Agents

Anti-fouling Agents for Marine Coatings This is specific for marine coatings or anti-fouling paints. The goal is to avoid marine organisms such as algae and molluscs to attach themselves to the ship. They would otherwise impact the ship performance (speed, maneuverability, fuel consumption).

Anti-Fouling Agents include both organic and inorganic chemistries. The use of some chemistries are restricted geographically for their effect on marine wildlife, so ensure to be compliant with regulatory guidelines for chemistry as well as use level.

 » Explore All Anti-foulants Here!


Mildewcides and antifungal materials are used in all exterior coatings where any moisture will promote the growth of organisms, such as mold, mildew and other fungi. Paints for interior applications where higher moisture levels are encountered, such as kitchens and especially bathrooms, also utilize mildewcides.

Biocides for Dry-film Coatings Since mold and mildew will grow even on glass in the presence of water, additives to prevent the microorganisms from establishing colonies are essential to keeping the coating looking pristine and free of discoloration due to mildew growth.

Zinc Oxide (ZnO) is by far the most common inorganic material used. There are several processed used to manufacture ZnO and it is important to adjust usage level based on type due to particle size distribution and therefore reactivity with the coating components.

Many organic materials work well alone or better in conjunction with ZnO, assuming the ZnO can be stabilized. The organics are highly-scrutinized and it is imperative that any used to formulate a coating are appropriate for the climate, but most importantly that they are approved geographically from the regulatory agency.

 » Choose the Anti-fungal Biocide for Your Coating Here! 

Other Types of Anti-microbial Additives

Nanomaterials are also used to prevent microbial growth - Silver (Ag) is used more often than others.

The effectiveness of such silver products is based on the slow and continuous leaching of superfine silver ions that interact with the metabolism of the microorganisms in various ways. For example, silver ions can inhibit enzyme activity, especially those containing sulfur. In doing so, they have a major influence on the energy metabolism of these microorganisms.

Products containing silver demonstrate a broad level of antimicrobial effectiveness, however, significantly less activity is observed for attack with fungus when compared to bacteria.

Most applications are where there is a concern for microbes (bacteria, viruses) developing resistance to an organic antimicrobial.

Criteria to Consider for Good Biocide Selection

In paints or coatings systems where antimicrobials are soluble and easily-dispersed during paint processing, the surface is well-protected against biocidal growth.

While, in systems where the antimicrobial is immiscible or difficult to disperse, a much higher level of biocide may be required to provide the same protection versus an antimicrobial with excellent dispersibility.

   Organic Antimicrobials
 Inorganic Antimicrobials
  • Non-reactive in total paint systems
  • Don't lead to gelation

  • Inert to UV
  • Do not leach from the film, thanks to their low water solubility

  • Can leach out from a coating over time with   repeated exposure to water (rain, humidity)
  • May be sensitive to sunlight (U-V)

  • Small particle size inorganic antimicrobials are reactive, especially w.r.t binders
  • Can lead to increased viscosity or even gelation

Among several factors, 5 important points to consider while selecting an anti-microbial or biocide for your coating system are:

Will it be used for a Waterborne or Solventborne Coating?

When a paint is formulated, there are several aspects to be taken care of. First of course, is performance of the paint as formulated. The other is the stability of the paint, which includes maintaining viscosity as well as minimum or no phase-separation.

If an antimicrobial is at least not miscible, it will separate and may form a thin layer at the surface of the paint in the container. Unless well-stirred, the paint applied to the substrate may not be uniform in the protection by the antimicrobial. Resistance to mildew and fungus may be poor as a result.

  1. Antimicrobial suppliers aren’t always specific about applications, as they want customers to use their products in as many applications (and therefore greater volumes) as possible. Many TDS’ show antimicrobial to be slightly miscible in water and only soluble or miscible in certain solvents.

  2. This becomes a key area for testing – compatibility. A good screening method is to make a very simple mixture of resin and solvent proportional to the coating and place in a small bottle or vial and shake vigorously. Incorporate the antimicrobial to determine if it is:
    • Compatible
    • Can be dispersed
    • Stays dispersed over time, or
    • Incompatible and cannot be dispersed or/and forms seeds.

  3. Try adding and shaking in, and if that doesn’t work, use a table/bath sonicator for 10 minutes.

Will it be used for Interior / Exterior Paints & Inks?

Market SB / WB Antimicrobial Type Chemistry
In-Can Anti-fouling Mildewcide / antifungal Other Organic Inorganic Blend O Blend
SB - Interior


SB - Exterior




WB - Interior







WB - Exterior








Paper Coating


Antimicrobials for Other Applications


SB / WB Antimicrobial Type Chemistry
In-Can Anti-fouling Mildewcide / antifungal Other Organic Inorganic Blend O Blend






Construction Products





Paper as raw material


The greatest application concerns are related to the regulatory environment and solubility. In the former, a paint using a specific level of an antimicrobial in one geography of the world, may not be in compliance in another geography due to use level or local regulations.

It also has to be known how the antimicrobial will be used. For example, there are FDA regulations that dictate use levels and chemistries with respect to indirect or direct food contact and others for adhesives, etc. In each case, the material has to be approved for use in that application, along with the maximum level of usage.

Solubility dictates toxicity which can affect humans on exposure to leachates present in water and plants due to solubility and runoff.

In which Geographies will it be used?

There has been a move to deregulate some products, so ensure that you use the most current MSDS from the supplier’s website and not rely on a document that your company may have filed.

Effects of Environment

  • Damp, humid, overcast environment / weather will be more harsh on an antimicrobial
  • Sunlight can dry out the surface on a regular basis
  • UV can itself kill bacteria (think southern vs northern exposure; mold and mildew vs. nearly none)

What Range of Microorganisms are Present?

In general, you won’t know specifically what microorganisms are present, but the environment in which the coating is applied dictates this. In an institutional setting, such as a hospital, doctor’s office, veterinarian, etc., there will be bacteria and viruses.

  • In an interior room with humidity >75% regularly, the conditions are prime for mold and mildew, although bacteria and viruses will also exist. 

  • Outside in humid climates and particularly on the northern exposure of a building, mold and mildew and algae will readily grow. Other microbials are not of interest. 

How to meet European Regulations? If in the US and related to food, what FDA regulations are required?

Today, the increased awareness of the potential toxic hazard of chemicals, and the evolution of the legislations towards very high standards of human, and environment protection, conducted to the implementation of more restrictive regulations for the control of chemicals.

Also nowadays 2 main piece of legislation have been adopted by the European Union:

  • REACH regulation: stands for Registration, Evaluation, Authorization and Restriction of Chemicals. It entered into force on 1 June 2007. Its objective is to improve the protection of human health and the environment from the risks that can be posed by chemicals, while enhancing the competitiveness of the EU chemicals industry. It also promotes alternative methods for the hazard assessment of substances in order to reduce the number of tests on animals.

  • CLP Regulation: Stands for Classification, Labelling and Packaging Regulation. It entered into force in January 2009. It introduces a method of classifying and labelling based on the United Nations' Globally Harmonised System (GHS).

Biocidal products are subject to the Biocidal Products Regulation (BPR) that was adopted in May 2012.

Biocides Performance and Safety Requirements

Although the new European regulations have changed the industry standard for active agents, the ability of fungal and algal to grow on both exterior and interior coatings makes the use of biocidal additives necessary. Several biocide active agents exist but only a small number of them respond totally to European regulations, industry needs, environmental and consumer demands.

Such demands represent a significant challenge for biocides manufacturers but it is possible to meet these requirements in terms of performance and safety.

For food compliance, ensure you are using the most current MSDS. Secure a letter certifying compliance and level usage from the antimicrobial supplier if in doubt.

When should you Consider Blends?

There is no universal biocide system that is compatible with all formulations and meets the requirements of the coatings manufacturer.

Among the various actives used for in-can preservation, there are:

  • Fast-acting biocides, e.g., O-formals, N-formals and 5-chloro-N-methylisothiazolin-3-one (CIT)
  • Slow-acting biocides, e.g., benzisothiazoline (BIT) and chloroallyl-3,5,7-azoniaadamantane chloride (adamantane)
  • Biocides with deficiencies in their activity spectra, such as BIT and N-methylisothiazolone (MIT), which have limited antifungal activity
  • Some biocides (e.g., isothiazolones) are known to be skin irritants and sensitizers, and 
  • Others they may release formaldehyde. These include O-formals, N-formals, triazines and adamantanes.

Bioactives suitable for dry-film preservation differ in water solubility. Two of the more water-soluble are 2-n-octyl-4-isothiazolin-3-one (OIT) and 3-iodo-2-propylbutyl carbamate (IPBC). Some, such as the fungicide carbendazim, have deficiencies in antifungal spectra. Carbendazim does not inhibit the common fungal isolates, Alternaria sp.

While the use of single active ingredients may be sufficient to prevent in-can microbial spoilage or dry film defacement, however, in many cases blends of actives may be used to optimize biocide performance. Depending on the blend, the advantages of using blends of actives may include:

  • Lower use levels
  • Fast-acting/longer term protection
  • Broader antimicrobial spectrum
  • Improved compatibility profile
  • Increased cost effectiveness, and 
  • Environmentally friendly end products

In addition, with varying regulations globally limiting the use levels of A-M, a blend or a blended material may meet the performance requirements as well as the regulatory requirements.

Commercially Available Biocides / Antimicrobial Agents

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Marc HirschAbout Marc Hirsch

Mr. Hirsch is a Senior Development Scientist and Principal Consultant at M&M Hirsch & Associates.

In his career, he has formulated architectural, industrial, military and specialty coatings. Developed applications and methodologies for sol gel coatings, earned his Green Belt in MAIC Six Sigma and trained for MAIC Black Belt, applied MAIC methodology to the CTR for several laboratory and manufacturing processes in Coatings resulting in substantial savings, successfully facilitated numerous ideation teams within his expertise as well as outside his core competencies. These included cross-functional and cross-business groups.

Prior to his current position, he worked at GE Energy (2008-2011) in the Simulation group; writing proposals to published specifications for training simulators for both fossil and nuclear power plants. At Luna Innovations (2004-2008) he was a Developmental Scientist in the Advanced Materials group. At Dow Chemical (1995-2004) he was the applications and development manager in Core R&D in the Coatings & Functional Polymers Group. He managed the TS&D group for coatings while at Dow (1995-99), and held positions at Rhodia (Laboratory Manager, Latex & Specialty Polymers (1989-95) and Development Chemist, exterior latex paints at Benjamin Moore &Co. (1979-82).

Mr. Hirsch consults to organizations to provide mentoring, coaching and leadership training, as well as the facilitation of problem solving teams.

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