The recently completed investigation report into the collapse of the thick plaster insulation system in Kontula provided many answers. However, it also raised new questions, the answers to which should not vary depending on who is asked.
Moisture damage, cracking facades and residents' concerns about the structural reliability. Insulating plasters are a hot topic, and sometimes people's concerns are justified: is the construction implementation and quality as good as it should be, and is the customer getting what they ordered?
The answer to this is easy: the client gets what is supervised. That is why during construction, the person undertaking the construction project carries out their own supervision. The goal is to ensure that the client gets exactly what they ordered. So if there is any doubt about the quality of the implementation, it is always right to raise the matter with the supervisor representing the client on the construction site.
The collapsed facade in Kontula provides a warning example of the client's failure to exercise supervision and its importance. Since personal injury was imminent, the Finnish Accident Investigation Board took the matter into its own hands.
In Kontula, additional thermal insulation was implemented using a thick plaster insulation system in two prefabricated apartment buildings completed in the 1960s in 2010. According to the investigation report, the system had been selected and designed correctly, and the outer shells of the concrete elements were reliably anchored to the concrete frame, as checked by a structural engineer, before the plaster system was installed.
From this point on - after the tensile tests and inspections carried out by the structural engineer were left behind - the housing company's shareholder's nightmare began, which is difficult to understand as a structural engineer.
A blur of errors and closing your eyes
The supervision and documentation of the construction site by the construction consultant were very disappointing. The construction site was not started and the foremen were not approved in accordance with the building permit. According to the investigation report, the construction products used were not what they were supposed to be according to the plans, i.e. products approved as a system and verified to work together.
The subcontractor used by the contractor for the implementation changed the insulation to thinner ones during the implementation and shortened the fasteners to the appropriate length conveniently with an angle grinder. The plaster mesh and fasteners had been ordered from someone else and only half of the number of fasteners according to the plans were installed. The installation of the fasteners and the correct positioning of the plaster mesh deviated from the plans and work instructions.
The alert partner successfully pointed out deficiencies in site safety and meeting practices, as well as the lack of a site diary, during the implementation. Unfortunately, the deficiencies were responded to by replacing the original construction consultant from the project due to “differences of opinion”. A new, experienced construction consultant was replaced, who approved the plastering work on the accident wall.
Although shortcomings in the work management and the kick-off meeting were revealed during this repair, the building inspectorate did not require any measures to be taken on the already completed wall structure. The end result was an incorrectly constructed end wall that was immediately complained about after the project was completed without being repaired later. A wall whose surface structure would collapse 14 years later after an unsuccessful repair had been made.
A costly lesson was not learned.
Basically, there is a place for looking in the mirror in Finnish construction processes if there have been negligence and they were known, but the difficulty of addressing them and disregard for the consequences could have cost a human life.
I am reminded of the Laukaa riding stables, where the completely avoidable loss of a young life led to an order signed by our then President Sauli Niinistö to inspect the structural safety of all large-frame buildings in Finland. So have we learned our lesson yet?
Judging from the accident investigation report, no. We can read how the incorrectly constructed and symptomatic wall structure was never opened and verified as defective.
From the customer's perspective, opening up a structure is often seen as too expensive, so the root causes of the problems behind the repairs often remain unsolved. Of course, this should not be the case, and competent designers do not ignore this. The problem is that competent designers can be ignored – replaced by someone else.
Is the cause in the sys or in the smithy?
The root cause then leads us back to the much-discussed isolated plastering. If you have been following various experts in the columns of magazines recently, the root cause of many facade damages has been identified as the isolated plastering system, in which errors during implementation and use become very visible.
This leads to an interesting circular conclusion: is it justified to blame a sophisticated solution for being implemented or maintained incorrectly? Or is it a self-fulfilling prophecy if we give the implementers permission to do whatever they want in advance? I think this kind of thinking is irresponsible and allows for evasion of responsibility in construction.
From the perspective of a product manufacturer developing systems, the situation is often strange: for cost reasons, the products in the system are wanted to be replaced with products that have not been developed or tested to work in the system. A bit like installing an incompatible electric motor or batteries in a Tesla that have not been approved by the manufacturer. Malfunctions occur under warranty, and when things finally go wrong, the finger of blame from outsiders is of course pointed at Tesla – the company that developed the system that was designed to work together.
Does the product manufacturer therefore evade its responsibility if the product is installed incorrectly, ignoring the instructions that meet the regulations? After all, the instructions are drawn up to be followed in order to ensure correct and safe operation in accordance with building regulations. And do other parties evade their own responsibility by pointing the blame at the product manufacturer?
I hope not, because all parties have something to learn from the incident so that something similar doesn't happen again.
The construction took a long time, with many errors and days
From the perspective of the product manufacturer – and the structural engineer – the accident investigation report is really interesting: even when installed incorrectly, the structure functioned structurally as designed and only persistently failed, reporting its problems long before collapse. What is worrying is that the problems were not detected in time, even though the thick plaster insulation system structurally functioned as expected in accordance with the principle of a resilient failure mode.
Despite neglect and serious deficiencies – and with at most half the number of fasteners designed – the system withstood its unintentional test load for 14 years, slowly sinking lower. The vibration and mass increase caused by the last repair were ultimately fatal to the apparently failed structure, according to the investigation report.
In professional terms, it can therefore be said that the thick insulation plaster system has up to double the security and a resilient fracture mechanism – even when the products do not comply with the system. However, a properly implemented thick insulation plaster system never involves the subsidence of the finished plaster work or damage to the movement joints. These are signs of the system's resilient fracture mechanism, which must always be responded to by finding out the underlying causes of the plaster movement.
An expert construction professional knows when the chosen solution is safe and healthy to use. However, nothing guarantees safety if the product is changed during implementation or the system changes completely during installation. In such a situation, even stricter GQRs (general quality requirements) or personal qualifications will not help improve the quality of construction if the threshold for addressing defects and errors is too high.
The author has worked as a structural engineer and structural safety inspector for large-frame buildings.
Petri Backström
CEO
petri.backstrom@rt.fi + 358 50 521 1888Construction product industry RTT ry, Finnisol ry
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