The preservation of interior walls and exterior building facades against the growth of fungi, moulds, and algae is a complex challenge, especially when considering health, environmental, and technical factors.

The health of the population depends in a very fundamental way on the living conditions we enjoy. The Commission on Social Determinants of Health of the World Health Organization (WHO) pointed out that health inequalities are the result of the context in which the population grows, lives, works, and ages, as well as the type of systems used to combat disease. The health conditions of our environment and the quality of our homes and the places where we work all impact our health. Sick building syndrome (SBS), which was first recognised in the 1970s, correlated the symptoms that people who use buildings or homes display to their exposure to chemicals, particles, or biological materials. Indeed, the hygienic conditions of the places we inhabit can influence the development of some diseases. The presence of fungi and moulds on the interior walls of our homes is at the origin, for example, of respiratory disorders caused by the inhalation of their spores.

The coatings industry began to evolve solvent-based formulations and water-based paints and coatings in the middle of the 20th century and these changes helped improve the safety, health, and environment impact of these products. However, these benefits were accompanied by the appearance of a new risk: contamination by microorganisms. When emulsified in an aqueous medium using water as a diluent together with the presence of organic matter, plastic resins are suitable materials for bacteria and fungi to proliferate. Microbial intrusion can occur throughout the life cycle of products, including in the manufacturing, packaging, and storage processes, as well as during the application and shelf-life phases.

Deterioration of surfaces by fungi and moulds

The growth of microorganisms on coatings in dry state alters their properties and causes changes in their functionality.

The dual protective and decorative function that water-based paints and coatings have on walls and facades is greatly compromised by the amount of water present in the substrate and in the materials (humidity from direct sources of water or condensation), atmospheric agents (such as rain and solar radiation), contact with chemical products, and by mechanical damage. The interaction between environmental factors and the materials in the coatings themselves creates the ideal conditions for the development of any airborne or animal borne spores that settle on these surfaces, leading to contamination by fungi and moulds which cause deterioration. Coatings degradate physically and chemically due to the action exerted upon them by fungi, as follows:

  • Physical or mechanical deterioration: the growth and movement of the microorganisms exerts pressure on the substrate which causes the film that covers it to break.
  • Chemical deterioration: the microorganism uses the materials of the water-based coating itself as a source of energy and its metabolic activity produces by-products that damage the coating.

The deterioration of coatings has multiple consequences:

  • Technical consequences: the coating loses its protective and functional properties, its covering power and adhesion decrease, its mechanical qualities and chemical resistance properties change, and its colour and gloss are altered.
  • Health consequences: the development of fungi and moulds on the walls of a building is a symptom of SBS and can cause disease.
  • Economic consequences: the costs of decontamination and rehabilitation of contaminated coatings, compensation payments, as well as losses as a result of the negative impact on the image of the parties involved.


For fungal contamination to develop on the surfaces of the coatings, three elements must be present: water, spores deposited on the coating surface, and the appropriate conditions.

Water is the most determining element for the development of microorganisms. Keeping materials and substrates free of moisture and avoiding water condensation on surfaces are the first key steps required to prevent spores present in the environment from flourishing into growing fungi.

One of the improvements in the quality of the coatings is their increased functional and decorative durability which thereby extends the repainting period. The very formulation of water-based paints and coatings helps to create harsh conditions for fungi and reduces the risk of contamination. The most effective ways to avoid deterioration of the coating due to the activity of microorganisms are the formation of a continuous and flexible film that repels moisture; the use of biocides that counteract the nutrients present in the system and control the possible intrusion of spores and fungi during the wet phase; and incorporation of fungicides that protect the dry film against the growth of fungi on the surface.

Dry-film preservatives extend the life of the coating 

New consumption patterns in society and increasing regulations are currently directing the water-based paint and coatings industry. The key goals are first, to formulate products that are protected against microbial intrusion so that they maintain their characteristics and functionalities throughout their useful lifespans. Secondly, these products must also have attractive labelling for the market which complies with regulations at a cost-effective pricing.

Once these coatings are applied, the environmental aggressions to which they are exposed degrade their components. Rainwater or humidity leach pigments, fillers, and also biocidal active substances, pulling them out of the coating and depositing them into the environment. Because of their inherent characteristics, fungicides are products classified as dangerous and toxic to the environment. The preservation of water-based coatings while in a dry state therefore presents a complex challenge: protecting the surface against the growth of fungi and algae while minimally impacting human health and the environment.

In this context, the biocide manufacturing industry is now allocating resources to the development of preservatives capable of controlling microbiological contamination with the least possible environmental impact while also maximising the safety of the people who handle both the biocides and the final products that reach the market.

Powerful and balanced protection with encapsulated fungicides and algaecides

The new generation of micro-encapsulated fungicides and algaecides are an optimal solution to protect paints and coatings against the growth of fungi and algae on their surface. They extend the useful life of the coating while also reducing the impact of biocides on the environment and improving handling safety.

The microcapsules are porous polymeric structures that cover the biocidal active substances and perform the dual function of protecting the biocide itself and reducing its eco-toxicological classification:

  1. Biocide protection: the porous microcapsules cover the molecules of the biocidal active substances, reducing the aggressive and debilitating action exerted by rain, humidity, wind, and insects, as well as that of UV rays and heat, helping to avoid the undesired yellowing and staining that some active ingredients can cause.
  2. Lower hazard classification: the porous encapsulation controls the diffusion coefficient of the biocides, which leaves a smaller amount of fungicide free in the aqueous phase and improves the eco-toxicological classification of the coating, allowing the labelling of the final product to be less restrictive.


The microcapsules control the diffusion coefficient of the fungicides and algaecides, lengthening the period of migration from the interior to the exterior of the capsule. This promotes progressive release of the biocide, prolonging its fungicidal and algaecidal efficacy over time, and making it more resistant to external aggressions acting upon the dry film.

The microencapsulation system developed by Chemipol makes it possible to obtain dry-film preservatives with a wide spectrum of activity, such as the fungicide and algaecide FUNGIPOL CP 123. These have a high concentration of encapsulated biocidal active substances that provide powerful protection against fungi, yeasts, and algae. The characteristics of the microcapsules allows the formulation of water-based paints and coatings free of volatile organic compounds which can therefore use ecological labels. Due to its formula, FUNGIPOL CP 123 is suitable for both interior and exterior coatings.


The use of micro-encapsulated biocides allows the manufacture of water-based paints and coatings with long-term fungicide and algaecide protection that are very resistant to leaching, stable in alkaline conditions, resistant to temperature and UV radiation, and which do not yellow or alter colour. Their use has a lower environmental impact and preserves coatings against fungi and algae more safely than traditional biocides. Encapsulated fungicides and algaecides can also satisfy different marketing options such as those required for water-based paints with ecological certifications.

September 2021, by Anna García, head of the paints and coatings business unit, and Eduard Broto.