The Finnish Building Products Industry (RTT) has compiled guidelines for construction industry operators to ensure the structural load-bearing capacity and safety of thick plaster insulation systems in new and renovation projects. The background is the investigation of an accident in Kontula, based on which the Finnish Accident Investigation Board issued a safety recommendation.
A serious incident occurred in Kontula, Helsinki, on 30 July 2024, when half of the surface structure of the second section of the end wall suddenly collapsed to the ground in one piece from the facade of an apartment building. In 2010, wool insulation was attached to the outside of the concrete element wall in the apartment building during a renovation project, and thick plaster was applied over it. As a result of errors made during the installation, the structure was renovated in 2023.
According to the safety recommendation, industry players should pay special attention to the structural load-bearing capacity of thick plaster insulation systems and to following the plans and installation instructions in both new and renovation construction projects.
The Finnish Building Products Industry (RTT) reminds us of the importance of ensuring the structural load-bearing capacity and safety of thick plaster insulation systems, i.e. three-layer plasters applied over insulation.
Basic principles for ensuring the structural load-bearing capacity of thick plaster insulation systems
- Compliance with plan: Thick insulation plastering must be carried out in accordance with the structural plans, the system supplier's instructions and the terms of the building permit. All deviations must be documented and approved by the designer and supervisor.
- Number and placement of fasteners: The number and location of fasteners must meet at least the requirements of the system supplier and/or the plans (usually at least 4–6 pcs/m², fastener spacing maximum 400–600 mm). In edge areas, the number of fasteners and the distance from the edge must meet the requirements, most often installed more densely.
- Correct installation of the plaster mesh: The plaster mesh must remain completely within the plaster mortar and must not be in contact with the mineral wool. The mesh must be overlapped and fixed according to the installation instructions, and each fastener must be installed in the correct position and equipped with the correct number of locking plates.
- Plaster thickness and mass: The thickness of the plaster layers must not exceed the maximum specified in the plan. Too thick plaster increases the mass of the structure and places excessive strain on the fasteners.
- Materials used: All materials (mineral wool, plaster mesh, fasteners, mortar, surface materials) must be approved by the system supplier and suitable for the structure in question.
- Monitoring and documentation: The construction supervisor and contractor must monitor the work phases very closely and document each step. A site diary, photographs and any inspection reports are essential for quality assurance.
You learned about the Kontula accident
According to the investigation report, the collapse of the thick plaster insulation system was caused by several factors, the most important of which were an insufficient number of fasteners, incorrect installation methods (for example, the mesh remaining outside the mortar), and inadequate supervision and documentation. In addition, the vibration and mass increase caused by the repair work further weakened the structure.
There were early signs of the risk of the structure collapsing, but no action was taken. The insulating plaster had significantly deteriorated and the expansion joint above the plaster was damaged. The sheet metal at the bottom of the plaster was warped and the plaster had caught on the storage room door below.
These factors together led to the structure's load-bearing capacity being exceeded and the wall structure suddenly collapsing.
Recommendations for construction industry operators
- Follow the system supplier and designer's instructions carefully. Do not deviate from the number of fasteners, the method of attachment, or the installation of the plaster mesh.
- Ensure the suitability of materials and work methods for the site. Only use approved products and ensure that all work steps are carried out according to the instructions.
- Document and monitor work steps closely. Photos, work reports, and inspection documents can be used to verify the accuracy and quality of the work afterwards.
- Respond to all deviations and detected problems immediately. Even slight "swelling" or subsidence of the finished insulating plaster, as well as damage to the connected structures and joints, are signs of structural weakness.
- Please note that weaknesses hidden in structures are not always visible from the outside. If necessary, the damaged structure must be opened and examined to determine the causes of the damage before repair work can be carried out.
A thick plaster insulation system is a structural system whose longevity and safety require precise adherence to plans and installation instructions, as well as careful supervision. Incorrect implementation and inadequate maintenance of the structures can lead to extensive and dangerous collapses.
The Finnish Building Products Industry (RTT) urges all real estate and construction industry operators to learn from the Kontula accident and invest in quality assurance of thick plaster insulation systems in all projects.
See also
- Recommendation of the Finnish Accident Investigation Board: Ensuring the strength of thick plaster insulation walls
- Safety investigation.fi: Accident Investigation Board investigation report
- Facade Association – JSY ry: Instructions for facade repairs (JUKO instructions folder)
More information
Petri Backström
CEO
petri.backstrom@rt.fi + 358 50 521 1888Construction product industry RTT ry, Finnisol ry
Jani Kemppainen
Manager, Technical Regulations and Legislation and Quality
jani.kemppainen@rt.fi + 358 40 541 8090Building Construction Industry Association