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Swirl marks in wood finishing.

Swirl mark is the problems in the wood finishing process. Swirl mark appears as the swirl or spiral on the wood surface. It will appear more clearly when we apply wood stain on the wood surface. The more stain wet wood the more swirl marks will be apparent. Swirl marks also will be very visible when the glaze is used at the finishing system; the glaze will fill and color the swirl and clearly visible at the finishing result.
Swirl mark problem is caused by the improper sanding process by the hand sander. The palm sander and rotary disc sander if it is not properly used will caused the swirl mark. Swirl marks won’t be happened when we sand using the big sanding machine such as: stroke sander or wide belt sander. The swirl mark is mainly happened when we press the sanding machine too strong to the wood surface in the sanding operation. It is often happened when we use the blunt sandpaper or too fine sandpaper to sand the rough and wood surface.  
Here are some tips to handle swirl marks problem.
  • Make sure the sanding machine is in good condition.
Palm sander works by vibrate the sandpaper, while the disc sander works by rotating the sandpaper. Both movements are causing friction with the sandpaper with surface of the wood. To produce a good sanding result, we need the stable movement. The unstable movement will cause problems in the sanding result. Put the sandpaper at the pad and run the machine and feel the movement. The sanding machine must be able to move and run stable and controllable easily. Stop using sanding machine when we feel the movement is “wild” and unstable. Fix the sanding machine first and make sure the machine in the good condition when we run the machine.
The second problem that often found is the pad. The pad is used as a place to attach the sandpaper that is moved by the machine. The pad needs to be thick and “elastic” enough to reduce the excessive pressure during the sanding process. Check the pad condition and make sure it is flat and thick (elastic) enough. The thin and uneven pad tends to produce excessive pressure on the sanding process which is the main cause of swirl marks.
  • The proper sanding technique.
Hand sander machine is small machine but effective and helpful to do sanding for small stuff or small area. It is portable handy and flexible with good result. However, this tool will only work well if we use it properly. The key is never press the machine too strong. Let the sandpaper does his job to sand and scrape the wood surface. Just make sure we use the right grade of sandpaper and use the sharp sandpaper. The sandpaper that has been blunt must be replaced because it does not work well. Do the sanding process patiently, little by little, and use the sandpaper grade by grade from the coarse to the finer, never skip the grade sandpaper. If we push the machine too much then we tend to press the machine to strong and it will create the swirl mark.  (See our previous article : pad sanding machine)
  • Checks the sanding before start the finishing process.
Swirl marks should to be addressed and corrected before the finishing process done. The revision and repairs after finishing the process will be hard and costly process.  We had to remove the finishing layer, re sanding do the refinishing which are difficult, expensive and never give perfect result.  Use the light or thin stain to help check the sanding quality at the beginning of the finishing process. (See our previous article : the wood sanding )
  • Selection the finishing.
Swirl marks will be apparent in a transparent wood finish. Swirl mark may not be visible for finish without wood stain or glaze application. We may obey the swirl mark for paint finish or natural finish especially when the finishing quality requirement is not too high. Although the swirl mark is considered as the indication for the wrong wood sanding process, but for some finishes we may continue to do the finishing.

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