Swirl Marks on Hardwood Floors: Why do they Happen? (Part 1 of 2)


Finishing hardwood floors is one of the more tricky aspects to installing floors. If the sanding or screening process is done improperly, swirl marks will appear on the floor.

Unfortunately, swirl marks tend not to show up until finish or stain is applied. This that if they do appear, you’ll often have to completely redo all your hard work, leading to lost time and lost money. Click here for some tips on preventing swirl marks.

But why do swirl marks happen in the first place? Read on below to find out some of the most common reasons.

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#1 Your grit was too aggressive

When you use a grit that is too aggressive for the wood floor you’re working on, it can create deep gouges or scratches that are quite noticeable.

A similar problem with swirl marks arise when the proper grit sequence is not followed. If you skip too many grits you will not properly sand away the scratch pattern. This will leave you with swirl marks and other problems.

#2 You screened too fast

Sanding, buffing, and screening is not a race. Going too fast will not allow the machine and sandpaper to do its job. When you’re using a buffer, you should walk at a deliberate pace.

#3 Particles or debris were under the screen

If you do not properly clean the hardwood floor before sanding, the debris can be pushed around by the buffer creating a dramatic swirl mark or scratch pattern. It’s also possible for the debris left on the floor to clog the sandpaper, which results in inefficient sanding.

#4 The machine is not balanced

When a buffer is not balanced correctly it will lean or pitch to one side. This can cause the sandpaper to create a gouge mark into the hardwood floor. Make sure you have an understanding of what your machine should feel like when it’s properly balanced. If you have any doubts, take it into a repair shop for a check up.

#5 The finish was not dry enough to be screened

If you start the screening process before the finish is ready to be screened you could run into trouble. The finish needs to have dried enough to be abraded and a good powder produced. Waiting two to three hours is typically sufficient time to wait before screening waterbased finishes, while an overnight dry is preferred for oil base polyurethanes.

Screening before the finish is at a proper dryness and hardness could give you a slew of problems, including swirl marks. Waiting the proper dry time between coats might seem like a long time, but it’s much better than having to completely redo a finish job because of finish problems like swirl marks.

#6 Floor is not flat

If the floor is not flat before the finishing stages the buffer will not perform correctly. When the buffer runs over the different highs and lows on the floor it will show different scratch patterns. If you find that the culprit is an uneven subfloor, here’s how to fix it.

#7 Finish was not clean enough

Much like the above bullet point, if there is any debris on the finish, when you screen in between coats it will cause abnormal scratch patterns. Make sure that during the whole finish process you are diligent about maintaining a clean environment.

Click here to read Part 2 of our blog series on swirl marks in hardwood floors, which talks about preventing swirl marks.

If you have any additional questions or concerns feel free to call us at (800) 737-1786 or email info@cityfloorsupply.com.

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