Pinning Down the Cause of Pin Holes

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Nov 10, 2021

Pin holes are blemishes on the surface of floor finish that form when the film pulls back from a small area of the floor surface. This forms tiny indents that look like pins pierced the wood floor. The finished floor appears to look and feel uneven, ruining the overall appearance.


Many causes of pin holes stem from applying the finish too thick. If coats of finish are applied too thick, film builds up and solvents are not allowed to escape. It will not dry properly, forming these indents. Additionally, if the first coat of finish is not dry enough before the second coat is applied, the conditions are perfect for pin holes to form.

Applying the finish in high temperatures is also a potential cause. Temperature can influence dry time because it can dry the finish too fast. If the finish does not dry as recommended by the manufacturer, it can cause pin holes or similar issues. Read more to learn about finish problems in warm temperatures.

Some pin holes are naturally part of the wood being used for a wood floor. For example, pinworm holes are around 1/16 of an inch and form when a wood-boring insect lives and feeds on the living tree before it is cut down. Most hardwood flooring manufacturers only allow a specific number of pinworm holes because too many will cause moisture problems with the wood. Pin holes can also refer to other wood characteristics like nail holes and open grain.

Prevention and Resolutions

To prevent pin holes from forming, follow all finish manufacturer recommended directions when applying floor finish. Understand how much finish is needed to coat a floor and how much time is needed for the finish to dry properly. Know the recommended maximum and minimum temperatures to apply finish and be sure the environment is between those temperatures. Make sure the finish is also not too warm or too cold as well.

Once pin holes form, repairs to the wood floor are needed. Before beginning, ensure the environment meets the finish manufacturer’s recommendations, including temperature guidelines. Scrape and recoat the floor using the proper applicator with the correct spread rates, both recommended by the manufacturer. Prior to recoating the affected areas, use an abrasive and scraper with the appropriate grit sequence to remove any pin holes from the floor. Once they are gone, refinish the floor. Check with the manufacturer for recommended repairs.

Basic Coatings® water-based finishes have faster cure and dry times than oil-modified urethane (OMU) finishes. With fast dry times, more coats are able to be applied in a day.  It takes water-based 2–3 hours and OMU 6–24 hours to fully dry. On average, it takes 7 days for a water-based finish to fully cure and 30 days for OMU. Read more about the advantages of water-based finishes.

To get in contact with a Basic Coatings representative with questions about pin holes and/or water-based finishes please visit this link.

Source: NWFA’s “Problems, Causes, and Cures 2018”

Photo courtesy of NWFA’s Problems, Causes, and Cures (3rd Edition, 2018).