Introduction
Cupping – The appearance of cupping is easy to spot: edges of the planks rise upwards higher than the centre of the planks. It looks like “u” sharp. This issue is absolutely not allowed when you open the flooring box. If it is happening, you can ask for a replacement or payment refund.
Crowning – Opposite to cupping, the appearance of crowing is the edges of the planks being lower than the centre of the planks. It looks like “n” sharp. Let’s discuss this issue today.
Understandably, most clients would be disappointed to discover that the engineered flooring they ordered from overseas has arrived with crowning issues. And although it would come as little consolation, they may be interested to know that there are two types of crowning: slight and severe. Slight crowning is discernible by calliper. Severe crowning, on the other hand, is obvious to the naked eye and can affect assembly.
Probable Causes
We should note that manufacturers are ultimately responsible for any defects. However, most importers who’ve had similar experiences would be curious to discover the following causes of crowning:
• The moisture imbalance through the thickness of the engineered flooring. The moisture of lamella is higher than plywood, then the top layer(lamella) part is becoming to expand. It leads to crowning.
• Slow manufacturing process time, mid-way though the flooring manufacturing process when the half-finished engineered flooring remains unprotected in the open air prior to profiling – especially in high ambient humidity.
• Natural oil coatings. Orders for flooring with a natural oil coating usually take 24-30 hours to dry between coats. However, during the rainy season, drying times can be much longer. The top layer(lamella part) also tends to absorb moisture in conditions of high humidity.
• Width. With widths of less than 240mm, for example, cupping with an offset of 1mm between the center and the horizon is hardly noticeable and has no effect on installation. By contrast, with a width of more than 240 mm, cupping of more than 1.5mm would be regarded as a quality issue.
• Thickness of lamella vs. plywood. The reasonable thickness ratio is 1:(2.7~3.5). For a floor that’s15mm thick, for example, the recommended thickness for lamella is no more than 4mm and for plywood no less than 11mm.
• Density of lamella. The KD (kernel density) of Australian timber such as spotted gum and blackbutt is higher than 750kg/m2, which exceeds the applicable ratio range. The usual solution is achieved using full birch plywood, compressed to increase density and offset stress.
Conculsion
To avoid crowning, flooring manufactures must control the moisture in lamella and plywood and increase the production flow rate. They should not attempt to coat natural oils during the rainy season or at times of high humidity. However, importers should allow more sufficient time for manufacturers to complete the flooring orders, so inevitably, this tends to dictate the timing of the manufacturing process. In the end, providing the best products with the fewest crowning issues depends on the combined efforts of both the importer and the manufacturer.
Author—John Ge Mobile: +86 13817612767 Wechat: John_Ge_Golink Email: john@guolianflooring.com
