The main reason for the gap in the use of solid wood flooring is the dry environment and the shrinkage of the wood. It is also the main problem faced by solid wood flooring in northern China. The size of the gap between the floors is closely related to the shrinkage factor of the wood used for the floor, the moisture content of the floor, the equilibrium moisture content of the environment, and the width of the floor. In the national standard for solid wood flooring (GB/T15036-2001), the solid wood floor moisture content is 7%~local equilibrium moisture content, which means that the moisture content of the factory floor is as long as it meets the above requirements, indicating that the moisture content of the product is qualified. If we do not consider the influence of other factors, there may be problems. In order to reduce and eliminate the problems in the installation and use of the floor, the state issued the "Wooden Flooring, Acceptance and Use Specification GB/T20238-2006", the standard was officially implemented on September 15, 2006. In the process of drafting the standard, a large number of relevant materials on the floor complaints were collected. Based on the opinions of all parties, the relevant provisions were formulated, taking into account the interests of all aspects (product production and distribution enterprises and consumers). In the standard, the relative humidity of the consumer environment is 40% to 80%. The gap of the solid wood floor under the correct use conditions during the warranty period shall be less than or equal to 2mm. Based on the above parameters, we discuss the relationship between the width of the solid wood floor, the coefficient of shrinkage and the gap created by the shrinkage of the floor.
First, the moisture content of the northern solid wood floor changes range
According to the “Wood Flooring, Acceptance and Use Specification GB/T20238-2006â€, the relative humidity of the consumer environment is 40%~80%. It also gives the bottom of the relative humidity of the consumer environment is 40%, and the environmental characteristics meet the standard requirements. Such conditions are normal use. If the gap of the floor exceeds the standard during the warranty period and the warranty conditions are met, the relevant party shall bear the warranty obligation. According to the requirements of winter heating in the north, the temperature of the room should reach 20 °C. Look up Table 1, the relative humidity of the air is 40% and the room temperature is 20 °C. The equilibrium moisture content of the floor is 8%, indicating the floor moisture content of the northern heating period. The bottom line is around 8%.
The upper limit of water content in the northern region should be the local equilibrium water content. According to our measured summer (the rainy season from June to September), the equilibrium moisture content of the floor is about 12%~13%. During the year, the change in floor moisture content (maximum-minimum value) in the northern region is about 5%. If the user's winter environment is too dry (the relative humidity of the indoor air is below 30%), the moisture content of the floor may vary during the year. It will be bigger. This change in water content occurs alternately every year. Therefore, the gaps generated each winter are relatively large. The user's use environment exceeds the standard for the time being, and the normal floor moisture content varies by about 5%. Therefore, it is necessary to study whether the dry shrinkage of the floor moisture content is reduced by 5% or more. When installing the floor, it is possible that the moisture content of the floor is not in the maximum state of the area, but the reserved gap should be reasonably determined according to the actual moisture content of the floor and the equilibrium moisture content of each area (related issues will be discussed later), In the wettest season, the floor is not bulged, and there should be no gap between the floor strips. At this time, the moisture content of the floor is still at its maximum. Therefore, we should all consider the maximum moisture content in the region as a basis.
Second, the relationship between the floor shrinkage coefficient and the floor gap
The shrinkage factor of wood is an important indicator of the dimensional stability of solid wood flooring when the moisture content changes. The shrinkage factor of wood varies significantly with the direction of wood cutting. The dry-shrinking coefficient of the string cutting material is larger than that of the diameter cutting material. In the case of the same change in water content, the string cutting material shrinks the most. If a string cutting material and a diameter cutting material are installed adjacent to the floor, there is a possibility that the gap has not exceeded the standard, when two standard string cutting materials are adjacent to the floor. Installation is likely to exceed the standard. In fact, the two standard string cutting materials are often installed adjacent to each other, and the dry shrinkage of the floor is the gap between the floors. Therefore, we focus on whether the dry shrinkage of the string cutting material is greater than 2mm.
When buying floor slabs, floor manufacturers should first understand the expansion and shrinkage characteristics of the wood used. Some can be found directly in the relevant books. For example, the wood properties commonly used in China can be basically found in Wood Science. We calculate and predict the shrinkage of the floor in the relevant area according to the dry shrinkage coefficient of the wood. The vast majority of imported wood can also be found in related books. It should be pointed out that the data of domestically produced materials is relatively accurate. Because of the different origins of imported materials, the differences in the material properties of the same tree species are great. It is recommended that the data to be re-measured will be more reliable.
The greater the shrinkage factor of wood, the greater the deformation with water content. Under the same conditions, the wider the floor, the greater the deformation. In summer (rainy season) and winter heating period in northern China, the moisture content of the floor varies about 5%. Within this range, if the width of the floor is 125mm and the shrinkage factor of the wood used for the floor is 0.33, the floor shrinkage Will exceed 2mm. When the dry shrinkage factor of the selected wood exceeds 0.45, the dry shrinkage of the floor with a width of 92 mm can exceed 2 mm.
The above analysis is to transmit a message to the production and distribution unit of solid wood flooring. Under the special climatic conditions in the north, the shrinkage gap of the floor exceeds the standard (wood floor covering, acceptance and use specification GB/T20238-2006) is not only the moisture content of the floor. If the material is too high, the material selection is unreasonable or the size of the floor is unreasonable, which may cause the shrinkage gap to exceed the standard. For example, the solid wood floor sold in the Northeast has a moisture content of 13% (water content in accordance with GB/T15036-2001), the width of the floor is 125 mm, the dry shrinkage factor of the floor string cutting material is 0.39, and the indoor ambient temperature of the user during winter heating. At 20 ° C, the indoor environment humidity is 40% (humidity meets the requirements of GB/T20238-2006). Look up Table 1: The equilibrium moisture content of the floor is 8%. The moisture content of the floor decreased from 13% at installation to 8%, and the moisture content changed by 5%. According to the dry shrinkage coefficient of the floor and the width of the floor, check the table 2, the dry shrinkage of the floor is 2.44mm (more than 2mm), according to the requirements of GB/T20238-2006, the gap of the floor exceeds 2mm should be repaired. It can be seen from this example that the product is qualified, the consumer's use environment also meets the requirements, and the gap of the floor exceeds the standard requirements. The original problem was caused by the unreasonable selection of materials or the excessive width of the floor. The same is true for the above conditions. If we change the width of the floor to 92mm and the dry shrinkage of the floor is 1.79mm (less than 2mm), no maintenance is required.
Also in the above conditions, the width of the floor remains unchanged at 125 mm. If the user's ambient humidity is increased to 55% (wet with a humidifier), the equilibrium moisture content of the floor is 11%, and the moisture content of the floor is 13% at the time of installation. Decline to 11%, floor moisture content changes by 2%, floor shrinkage is 0.98mm, in line with GB/T20238-2006 requirements.
Third, the conclusion
From the above analysis we can draw the following conclusions:
1. The width of the solid wood floor should be determined according to the dry shrinkage coefficient of the string material used. The tree with large dry shrinkage factor can be made into a relatively narrow floor.
2. In the solid wood floor used in northern China, when the width of the local board is 125mm, the dry shrinkage factor of the wood string cutting material used should be less than 0.33. When selecting a floor with a width of 92 mm, the dry shrinkage factor of the wood string cutting material should be less than 0.42.
3. Appropriately increase the relative humidity of the use environment to reduce the gap created by the floor shrinkage. Distributors should provide consumers with the environmental requirements for the floor they purchase.
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