Wood exposed to moisture or free water becomes susceptible to microbial growth over time. Remediation of the growth may be a better option than tearing out and replacing all the wood with new. An overall perspective with knowledge of all relevant parameters is required in order to make the right assessment and decision. A preliminary summary of the current situation regarding decontamination has been carried out by RISE and is briefly presented below.
About microbial fouling - legislation and scientific studies
Regardless of the construction phase in new production or in existing buildings, the law states through the Environmental Code and the Planning and Building Act that growth that can cause damage or inconvenience to human health must be removed. The legislation on chemicals emphasises that damage resulting in the need to use chemical products and pesticides should be avoided if knowledge and techniques for this are available. Once pesticides are used, only the intended use according to the instructions is authorised. Scientific studies and authorities advise against the use of chemical agents to clean up growth on wood. The reason is that they seem to have a limited effect and their use carries the risk of increasing the amount of pollutants in the indoor air. There is also a risk that the methods may only kill the microbial growth without removing it, and that even dead/inactive growth may pose health risks.
The research on moisture damage and negative impacts on human health is complicated to evaluate. It requires assessment by medically qualified people and demonstrating the links between moisture damage, growth and health parameters. The challenge is to define the boundary between harmful and non-harmful.
Decontamination of wood
Microbial growth on wood is remedied, using various decontamination measures to clean the wood material from the growth, unless the wood material is completely replaced. In the construction phase, if the building has been exposed to precipitation or if protection against moisture and water damage has been inadequate, there is a risk of damage. Moisture safety needs to be prioritised to a greater extent in many cases, and relevant strategies for managing moisture safety are already needed when planning the budget and design. The interviews with, among others, remediation companies in the project "Remediation of microbial damage to wood in buildings - a compilation of the current situation in the industry, laws, methods and areas of use" show that sanding of wood surfaces is the most commonly used remediation method, followed by ice blasting and the use of chemical agents to clean and bleach the wood surface.
Buildings that are exposed to free water or high moisture levels over a long period of time can suffer from rot and insect damage. Decay and insect damage is addressed by replacing damaged material and/or treating with authorised pesticides.
Moisture damage
Events where water to a greater or lesser extent causes damage to wood in buildings can occur. Prompt action and limitation of water exposure results in significant savings as the onset of typical moisture damage and the start of microbial growth can be prevented. During the construction phase, it is important that the organisation is prepared for incidents and can act quickly. In existing buildings, if and when preparedness is lacking, the time for detection of water exposure and before action is taken can be long and thus the risk of typical moisture damage occurring is high. Unlike water exposure to clean water, exposure to wastewater or other water containing microorganisms and contaminants always requires remediation.
Addressing moisture damage - industry practice and remediation
When moisture damage has occurred on wood in buildings, one typically thinks of visible mould growth and the smell of an earthy cellar. This is only partly correct because mould growth is not always visible to the naked eye. The limit of what is considered to be affected by mould growth in the wood structure and therefore damaged is not easy to define. Industry practice is used here, with sampling and analysis and assessment of growth with subsequent remediation and follow-up of the effect with new sampling.
Remediation of moisture damage
Remediation of moisture-damaged wood is mainly carried out by sanding the wood surfaces followed by blasting with carbon dioxide rice and, to a lesser extent, planing. The use of chemical products is also common, including cleaning agents, pesticides and/or general chemicals. The Environmental Code is the basis for the requirement that operators must have knowledge of the activities being carried out. There is also a requirement to avoid unnecessary use of chemical products.
Mechanical decontamination
Mechanical methods mean that the growth is physically removed with an object. Physical and mechanical removal methods are not regulated by pesticide laws. Methods include examples such as sanding, planing, blasting and scraping. The choice of mechanical method should be adapted to the substrate and the type of damage (see the section on standards above). The contractor should know how much of the surface layer of the infested timber needs to be removed in order to make the surface free of microbiological growth while avoiding unnecessary removal of material. It is also important to consider the working environment for those carrying out the decontamination and/or being in the vicinity of the decontamination area. There are level limit values for organic dust and wood dust (AFS 2018:1).
Chemical products - detergents
Detergents follow the legal requirements of the Regulation and EU level detergents. These products should have a good cleaning effect without being harmful to human health or the environment within the defined area of use. Pesticides are used in two categories which are surface disinfectants and wood preservatives. Disinfectants have a control effect that is temporary (< 3 months); as wood is a porous material, it is more difficult to disinfect and the effect is short-lived, only a few days. Wood preservatives with a longer-term effect used in existing buildings to protect or control organisms must be authorised for this purpose. The main requirements are that the product must have a proven benefit, be effective and not cause unacceptable damage to human health or the environment. Historically, there have been products that caused environmental and health problems and lacked efficacy for their intended use.
An agent that works against one type of organism does not always work against another type of organism. For authorised use, the right effect on the target organism with the right application method and dosage needs to be matched. Chemical products intended for the control of organisms can be effective when other methods of remediation are not available. A balance needs to be struck between the overall benefit and the risk of damage caused by chemicals. The benefit can be positive from a sustainability perspective, with savings for the environment and the economy. There are a few examples where chemical pesticides have a clear benefit. Infestations of dry rot and other mould fungi occur regularly in wooden buildings where water damage has occurred over a long period of time. Remediation requires the identification and removal of the cause of the water damage and the demolition of parts of the structure affected by the mould. As the fungal hyphae can travel 10s of metres from the water damage, the entire building would need to be demolished to ensure that the entire infestation is removed. To do this, chemical treatments are applied to the remaining timber so that any residual fungus cannot continue to grow in the event of further water damage. Similarly, timber foundations, with piles and rust beds, can be similarly saved in the event of a rot fungus infestation, avoiding the need for piling a new foundation structure and resulting in significant savings.
Chemical products - general chemicals
General chemicals, which are also pesticides, are sometimes incorrectly used to sanitise wood growth. Ethanol used for hand disinfection and for disinfecting non-porous surfaces in buildings has a proven effect over a number of hours. On wood, which is porous, this favourable effect is lacking as the ethanol is absorbed into the wood and the concentration decreases rapidly. In addition, there are organisms that can use ethanol as an energy source which can make the attack worse. Due to ignorance, ethanol is very commonly used as a sanitising agent against wood growth in buildings because ethanol-based products are readily available.
This is an article from our magazine Trävärden, view it here! (Link)
