Cold Check, the Examination for Cracking Problem in the Wood Finishing

Cold check is one of the basic tests for the finishing layer for the furniture. Cold check is an examination to see the behavior of the finishing layer due to the temperature changes. When we make furniture products to be exported to overseas destinations, the test is the important tool to make sure the product will be safe during the shipment. The product from Asia will need about 3-month trip to arrive in the US or Europe, and during this time there could be temperature fluctuation from day to night or weather changes. The temperature fluctuation during the journey may damage the product. The cold check is the important tool to make sure the finishing is strong enough to pass the temperature changes during the shipment. In the series of finishing tests, the cold check is usually done at the first time, before the adhesion and hardness test. 

crack on the finishing

How to do the cold check test.

The cold check for the finish layer is usually done to the sample finish panel. The test for big objects needs a freezer and oven with big room that is expensive. The small size panel is enough to examine the finishing system. If the sample panel is passing the cold check, then we can consider that the finishing system is safe. The finishing process for the panel should be the same as the production process. 

Take the finished panel as the sample for the finishing process. The finish must be completely dry and perfectly cured. Put the panel in the refrigerator and chill it to the temperature of 0 degrees Celsius for 1 hour, then take out the panel and put it in the oven and heat it to the temperature of 80 degrees Celsius for 1 hour. Then take out the panel from the oven and check the panel. If there is any defect, crack, or check at the panel, then we stop the test. A one-time process of cooling and heating is called a cycle. If there is no damage at the finishing layer, then we continue doing the cycle.

The test result is expressed by the number of cycles that are successfully passed by the sample without any damage. In the condition when there is no check found, then the test usually is ended at the 8th cycle.

The things to be considered to pass the cold check.

• The quality of the finishing materials.

The good-quality material is needed to make the strong layer of finishing. Most of the finishing problems are caused by the poor material. The poor material could be caused by the material itself or by improper mixing and application. Therefore, we need to check the finishing materials before using them. Check the technical data, the expiration date, and the guide on how to use it. If we need to mix or cut the material, make sure the proper thinner is used. Make sure we well agitate the mixture; check the viscosity and the physical look of the coating. 

Perform the finishing process step by step, following the drying time of each material. Use the material with the same type from the first step to the end whenever possible. The finishing with a full NC system will have less risk of having finishing problems compared with the NC on PU system, NC on Ac, or NC on UV. If we use the combination coating, then we need to make sure they are compatible with each other. See our previous article: The compatibility of coating application.

• Avoid too thick film.

The thicker finishing layer tends to have a higher risk of getting crack problems. Use the coating in fair amount, it is also will safe the material usage. If the close pores finish needed, then we can apply wood filler to reduce the consumption of the coating. Do good sanding for every layer coating application. Make sure we don’t exceed the maximum thickness of the film finishing recommended. The NC finish is recommended to have a maximum 4 mill dry film coating to avoid the crack problem. The PU and UV finish could have thicker film coating, but we should keep the finish thickness as low as possible.

• The substrate condition.

Some cases of cracking and checking at the finishing layer are caused by the substrate. The wood or wood product that has a high moisture content will release water and contract upon the heat. The wood contraction leads to the crack problem, which will seem to be the finishing problem. Therefore, always check the moisture content of the wood or wood products before starting the finishing process; make sure it has dried before the finishing process is started.

Some natural sources, such as leather, pandanus, water hyacinth, see grass, and rattan, are elastic and result to the crack problem. The special treatment is needed to handle the elastic substrates. We need the special finishing material and special process to accommodate the movement of the substrates