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Sunday, July 5, 2015

Marring problem at the wood finishing

Marring is fine surface scratches at the surface. Marring generally is distributed over a relatively large area that typically spoils the appearance of a surface coating. People are easily to get confuse between mar and scratch. Both marring and scratch resistance are considered expressing the strength of finishing layer. When they find mar problem at the finishing layer then they think that the finishing is not strong enough and they ask for stronger finish.  But actually mar and scratch is two different things. Mar resistant actually is not really related with the strength of the finish layer as the scratch resistant.  Marring is the fine scratches on the surface and only gives effect to the surface finishing layer without affect the body of the finishing layer. Marring problem will not disrupt the protection function of the finishing layer but only ruin the appearance of finishing. While the scratch involves to the entire finishing body and damage of the whole body of the finishing layer. The scratch problem sometimes could make the substrate is open and will affect the protection function of the finishing layer.  Scratch resistant is highly depend to the strength o the finishing especially the adhesion and hardness o the coating film. While the mar resistance although is still affected by the hardness of the finishing layer but actually is more depended to the “slippery property” of the surface. 

mar at the wood finish
mar at the black finish


Although will not really affect the strength of the finishing layer, but the mar still consider problem in the finishing especially when we deal with high end product. The good finishing layer is always expected to have good mar resistance; any mar problem at the finishing will ruin the finishing appearance and then lower the finishing quality. 

Here are some things that we can do to avoid marring problem at wood finishing.
  •  Use the hard coating layer.
Marring resistant somehow is still related to hardness of the coating layer of the finish. The hardest the coating, then the less risk to get mar problem. The fact is mar problem is often found  at the finish that uses 1 component coating that is relatively "soft". With pencil hardness test the 1 component coating (NC, Water based, Shellac)  will give HB or B score that is relative low.
To avoid the mar problem we can use the harder coating to the finishing. We can use the 2 component coating such as: AC or PU coating or UV coating.  The PU or AC coating that dry with the chemical reaction will give 1H or 2H with pencil hardness test will surely give harder film layer and will reduce the risk of mar problem at the finishing. The UV coating even is 1 component but it is dry with chemical reaction and could give the harder coating layer then the PU or AC coating will also give better mar resistant to the finish.
  • Apply wax at the finish surface
Instead the hardness, mar is highly depend to the slippery property of the surface. The smooth and slippery surface will make any force received by the surface is ” slipped” without leave scratches. Some finishing materials manufacturers have provide fluid lubricant that can be applied on the finishing surface. The material usually is liquid contained wax that is work as a "lubricant" to add he "slippery" properties at the finish surface. The liquid can be applied on the top coat after the top coat dry. The wax can integrate with the coating to increase the slippery property of the coating surface and help to minimize the risk of mar problem at the finish.
  • The choice to the color and appearance of the finishing.
Marring is associated with finishing appearance. The fact mar problem usually appear at the finish with dark colors. The risk to get mar problem will be higher if we use the extremely gloss (very high gloss or very low sheen). The finishing with NC system may not get mar problem for white or light brown color. But we will get the mar problem for the dark brown or black color, full gloss or dead mat sheen finish, even though we run the same material and the same system.
Actually with the same system and same coating type the finishing layer will give the same strength and hardness. At the light brown or white color actually there is mar (fine scratches), but it is difficult to be seen and tend to be invisible. While at the same scratches at extremely dark color, high sheen or low sheen will obviously seem and then is detected as problem. Base to this fact, then every time we make finishing with dark color and he extremely high or low sheen we must consider to the mar problem risk. We may need to consider using the hard coating layer or doing special treatment to minimize the mar risk.
  • Use standard testing to observe the mar resistant
Sometime the mar is very easy to happen. The fact is we don’t need hard power to make mar. The hard material such as nail tip or even dust at the surfaces will easily create scratches to finish surfaces without any strong energy. Even the strongest coating such as PU or even the UV coating are actually easily to get scratches, then when we observe the mar resistant to the finish we should use the standard test (we can refer to http://www.astm.org/Standards/D5178.htm178 - 13). Any test with nail, finger or other method cannot be used since it wont, give a measured result.
Then finally we always need to refer the marring resistant of he finishing to the standard coating properties. We need to realize that every type of coating actually has limitation and we should not expect the finish strength to over its naturally properties.