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Mapei Ultracot

The paradox of saving

A wooden sports floor in an indoor sports stadium, under-floor radiant panel heating and parquet blocks that move under the baskets were just some of the problems to be overcome in a new, particularly intricate job

The case we present here can be seen as an example of the paradox of sav- ing, i.e. a good parquet fitter should never “save” when it comes to the materials that dictate the final success of his work. It would be a bit like a cowboy builder looking to save money by “forgetting” to add cement to the screed mix, leading later to not only technical problems, but also extra costs for both the customer and the builder himself. Unfortunately, as various inspections and surveys revealed, the case in hand is the outcome of having forgotten something that led to problems further down the line and which took a lot of money to set right.

The problems on the “games court”

The object inspected was an indoor sports floor, a large wooden surface installed inside a sports hall that hosts regular events at both a national and international level. The experts had been asked to consider both the supply and the installation of the wooden flooring for sports use, with special attention to how the wooden flooring had been fitted, as this was used for both basketball and volleyball championship matches. The floor consisted of a double framework of wooden joists (called “tozzetti”) with an overlying double framework of decking planks (the lower planks parallel to the longer side of the court, the upper ones perpendicular to the lower ones), a nylon canvas and finally the wooden parquet boards. There was also a quite rare feature for a sports hall: the wooden flooring had been laid on top of a floor heating system. The complaint concerned the “gaps that exist” between the extreme peripheral parts (heads or ends) of the boards, particularly evident in those areas close to the baskets at either end of the court. Indeed, the owners complained that the individual boards in the wooden floor “widened” at the ends, often during games of both basketball and volleyball. The situation was made worse by the non-alignment of the lines marking the court areas, which led to many disputes during the course of games. Protests were so animated that the owners saw fit to take the case to court. Over the course of several inspections, it was also found that the parquet boards with gaps at the ends were never the same and never in the same place.
How could this be possible? A defect cannot just appear and disappear or rather move randomly across the surface of a floor. The only common element was that the gaps between the boards were generally found at either end of the court, near the baskets, i.e. the areas most subject to stress and pressure, where the athletes concentrated their efforts.
We were asked to investigate the matter in order to understand the origin of the defect and, of course, solve it.

In search of a cause

The owners had started to raise objections as early as the final testing of the newly laid floor. Their first few letters had, in fact, pointed out that “the parquet sports floor has problems regarding gaps appearing between the boards both lengthwise and transversely.” This problem had also been reported by the various sports clubs using the sports hall.
These reports were accompanied by photos showing the areas of the court near the baskets, clearly showing that the position of the gaps between the boards changed each time. Meanwhile, the floor fitters rebutted with the claim that the gaps were due to the excessive temperature of the radiant panels in the floor heating system, but after an audit by a technical expert appointed by the owners, it emerged the temperatures posed no risk to the stability of the floor:

  • Parquet surface temperature = max 25.6 °C and min 25.2 °C.
  • Parquet temperature where covered by the PVC platform = 26.9 °C
  • Air temperature under the floor = 23.4 °C
Other abnormalities then emerged, which, although not actually rendering the floor unusable, did affect the aesthetics: the ends of numerous boards were virtually right up against each other, meaning there was no offset distance between them. The presence of shrinkage or cracks along the longitudinal side of each boards was also noticed, which was in turn composed of individual layers of parquet, although there were no particular anomalies in the size of the boards.
In essence, the shrinkage was minimal and in line with the physiological behaviour expected of wooden flooring on a heated substrate.
However, the flooring had been raised above the heated surface by inserting wooden blocks (“sleepers”) and loadbearing joists upon which the parquet rested. In other words, joists (double oscillation) had been placed on these wooden blocks, followed by a second decking layer (the counter floor) and finally the final wooden flooring. Furthermore, two polyethylene sheets had also been laid: the first under the heating system pipes between the bottom surface and the base of sleepers; the second between the counter floor and the individual parquet boards making up the sports floor. Another important factor was that the wood used had all the necessary certification, namely DIN V 18032-2:2001-04 dated 28-02-2005 by DIN CERTCO in Berlin. After taking into account the findings of these technical investigations, it became clear that the work had been carried out without taking into account the manufacturer’s technical requirements, thus compromising the warranty of the product itself, since it could no longer respond to the basic requirements for which it had been approved. Moreover, it also emerged that the installation instructions, which indicated the size of the nails to be used as well as other obvious technical matters, had been ignored. In fact, the movement of the end boards and their continuous change in position made one think that the problem lay in the anchoring method rather than being connected to the heating system. It therefore became necessary to proceed with an invasive investigation in order to verify the presence or absence of the anchor nails and their size, given that these were required in the technical documents accompanying the product.

“Site” survey

After removing at least three of the parquet boards, it was found that the first and the third boards had no “fixing nails”, while the second had 4. Furthermore, the following floor structure was observed: 1) polyethylene sheet laid under the parquet surface and on top of the counter floor; 2) the counter floor consisting of wooden elements (spruce) 90/95 mm wide with a variable space (distance from centre) between the various strips, ranging from 50 mm to about 55 mm; 3) the initial joists consisting of 2 single wooden elements with flexible coupling, positioned about 450 mm apart; 4) wooden sleepers with nominal dimensions of 93 mm wide and 80 mm high (the official measurements were 100/ 120 mm wide and 60/80 mm high); 5) polyethylene sheet laid directly on the raw concrete floor with the heating system pipes clearly visible on top of this. With regard to the temperature of the parquet flooring and that in the “air gap” created by inserting the wooden sleepers, the investigations found no negative or unexpected values, including the dynamic balancing of hygroscopic wood as foreseen by UNI EN 1264-1/2/3/4. However, when it came to the question of how the parquet sports floor had been “nailed”, it was found during the invasive investigation that the wooden elements had been nailed in an approximate manner, not in line with the technical documentation received (in particular, the specifications in the installation instructions drawn up by the manufacturer and attached to the DIN V 18032-2:2001-04 certification dated 28-02-2005). For example, there were no nails in two of the three boards and the “nails” used were inappropriate for the intended use of the sports floor. Indeed, nails of the wrong size had been used, incapable of withstanding the envisaged stress: 1.2 x 40 mm long with a 1.8mm head instead of the recommended 2.2 mm x 40 mm long nails with a 7mm head. Only after the invasive investigation was it possible to detect the lack of nails in the two of the boards examined. Whilst it is certainly true that such a small number of boards cannot be considered representative of the entire floor, one can assume that the practice to simply “nail down the boards from time to time” had been repeated right across the surface given the observed dynamics of the way the blocks “had grown apart” several times and in a “random” manner. Without prejudice to these findings, there are currently no sector-specific regulations regarding the installation of wooden parts to be nailed down giving the precise dimensions of the nails to be used (nor were there any at the time of the technical inspection), yet contrary to what is usually the case, the fact that there were technical documents with specific installation instructions from the manufacturer means that precise elements do, in fact, exist that allow one to assess the causal link.

All suspicions therefore fall on the “NAILING”

From the findings of the technical inspections, one can safely state that not enough importance was paid to how the boards should have been nailed down when the sports floor was being laid, a crucial oversight given the high levels of stress and strain (attrition) that such floors are subject to. Moreover, after reading the manufacturer’s installation instructions, provided with the certification from DIN CERTCO of Berlin (DIN V 18032-2-2001-04 dated 28-02-2005, the whole bundle having been given to the customer), it is evident that the people responsible for fitting the floor did not follow some of the basic technical instructions. The invasive investigation has clearly afforded us the chance to discover some technical deficiencies that form the probable cause of the problem.
We have been able to verify the following:

  1. The fitters did not nail down the floor – a stage required by and foreseen by the manufacturer and clearly indicated in its technical instructions provided with the DIN certification – in a manner compliant with the mandatory technical instructions.
  2. There are currently no sector-specific regulations regarding how such wooden parts should be nailed down (nor were there any before or at the time that the sports floor was laid). The only exception is the European technical specification UNI/CEN/TS 15717 dated October 2008 General Guidelines for Floor Laying, which, with regard to the laying of wooden floors requiring nailing, reads: “the type of screws/nails must be selected in accordance with the manufacturer’s specifications.”
    In fact, as can be seen in the technical instructions attached to the product certification documents, the manufacturer did provide specifications in this sense, i.e. 2.2x38mm T-nails should have been used to fix the parquet boards to the counter floor. Furthermore, one can assume that the fitters used the same non conforming nails to join the two load-bearing levels (the double oscillation joists and the counter floor) instead of the 2.2x32mm Tnails specified by the manufacturer.
  3. The gaps between the parquet boards were caused by these boards slipping at the moment of impact (attrition) by the rubber-soled shoes worn by players during basketball games.
  4. The complaint that the gaps between the boards “change their position”, as proven by the fact that certain boards open and then close after manual traction stress, confirms the fact that the type of nailing used, where present, and found to be non conforming with the official technical specifications, was insufficient to “withstand tension in the boards as a result of the surface friction.”
    The heat coming from under the floor cannot be considered to cause the detachment of the boards (gaps between boards), despite the fact that the heat in the air-gap under the wooden floor is propagated solely by natural convection.
  5. The gaps, in varying positions, only occurred at the extreme ends (heads) of the boards and were of differing dimensions; these then “disappeared” if stressed, i.e. the boards were made to slide back and so close the gap.
    The fact that these gaps regularly occurred can be further confirmed by the presence of “grouting substances” used to close the gaps and found at the ends of the boards.
    There is no information about when the grouting substance was first applied, although certain photos lead one to presume with a fair amount of certainty that the gaps started to appear between boards from the very time the court lines were first drawn on the floor.
  6. The constant heat, as is the case with all heated supports where a wooden floor comes into direct contact with a hot surface, creates shrinkage in the wooden elements in a longitudinal direction only, to a varying degree depending on the timber used and the direction of its grain. For instance, wooden elements obtained from tangential-cut elements will shrink at least three times as much as radial-cut elements.
  7. In the case in hand, we have only found localised gaps (in the playing areas) of varying dimensions at the front end of individual boards; no similar gaps or other deformations caused by shrinkage have been found across the whole surface of the floor. If the under-floor heating system had been the cause, we would have expected similar problems across the entire surface of the wooden floor, not just in the playing areas, i.e. under the baskets.

CONCLUSIONS

To sum up, after several months of meetings, inspections and discussions, we have reached the conclusion that “nails were missing”.
The nailing of the floor was done in a discontinuous manner, using nails that did not comply with the manufacturer’s installation instructions and this saving in nails led to a whole series of incredible problems that required the intervention of many experts.
Was it really worth it?
We hope that this case will serve as a lesson when facing similar jobs in the future. The old adage “the cheapest is the dearest” has been proved true once again.

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