Why do fisheyes appear in hardwood floors?


Why do fisheyes appear in hardwood floors during the finishing process? And what, exactly, are they? These are some of the most common questions coming from hardwood floor mechanics.

Fisheyes are light depressions in the finish with smooth, rounded edges and a concave center. They are the result of some sort of contamination, and they are usually created during the recoating process.

Once you’re aware of the most common causes of fisheye, you’ll be prepared to prevent this unsightly problem from appearing the next time you recoat a hardwood floor.

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The biggest problem: Solvents from previous finishes

The biggest cause of fisheye is that the solvents from a previous coat of finish haven’t fully evaporated before a new coat is applied.

Liquid solvents must be allowed ample time and the proper conditions to evaporate before a new coat is applied, or else the residual solvent will act as a contaminant.

The solvent’s interaction with the newly-applied coat of finish creates a surface tension that the new finish cannot envelop. The resulting lack of “wetting out” is what produces the fisheye.

Other chemicals can also act as contaminants

Improper drying methods during the recoating process may be the biggest cause of fisheye, but compounds like wax and silicone can also cause fisheye if they’re accidentally allowed to contaminate a floor. In these cases, they’re usually brought in on work equipment such as boots or buckets.

Chemicals used by the average homeowner may also lay the foundation for fisheyes to appear.  Oil soaps and citrus-based cleaners can penetrate into the depths of the finish and act as contaminants when the floor is next recoated.

To prevent cleaning chemicals from seeping into the finish of your hardwood floors and becoming contaminants, make sure to follow the instructions on the product packaging. If the manufacturer calls for only one ounce of oil soap to a gallon of water, listen to them instead of blindly pouring the soap into your mop bucket.

Test your system to avoid the appearance of fisheyes in hardwood floors

You can never be 100 percent certain about the processes and products used by people who have previously worked on a floor, so recoating a floor that has previously been done by someone else can be risky business. (Some contractors actually refuse to perform recoats for this very reason.)

Sanding down to bare wood and applying completely new finish allows for the most control over a work environment and process, and thus affords the most protection from fisheye.

But if you’re recoating a floor that was previously coated by someone else, luckily you have the option of testing your system in an inconspicuous area of the floor to make sure there’s no contaminant that will react with the new finish.

If you notice something wrong while working, stop!

If you go about recoating the floor and begin to notice round marks appearing in the finish while you are working, stop immediately, because this likely means that there is a solvent or some sort of contaminant present.

If you are able to determine the source of the contamination and the exact solvent that is causing the problem, you can use another solvent to remove it. Make sure to completely eliminate the source of the contamination from your workspace, and then to allow the solvent used to eliminate the original contaminant to properly evaporate before applying the next coat of finish.

Allow for proper air circulation and leave ample time in between each coat

A great trick of the trade you can use while coating floors to help prevent fisheye is a box fan with a timer. You can set the timer to turn the fan on once the finish has reached a tack free state. This will allow for a proper drying process to commence, and for the solvent to fully evaporate before you apply the next coat of finish.

Also be sure to read the finish manufacturer’s drying instructions. Pay close attention to directions and suggestions about the best conditions in order to ensure that you’re leaving enough time in between each coat.


If you have any questions about how preventing or combating fisheye, reach out to City Floor Supply at (800) 787-1786 to speak with a hardwood flooring expert.


[Photo credits: flickr.com/cutey5, flickr.com/aisforangie, flickr.com/epicfireworks

All photos used in this post are covered under the Flickr Creative Commons license.]

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