Hardwood Flooring Polyballs

What Are They?

Polyballs are beads of finish that protrude from cracks in the floor when the moisture content (MC) of the wood rises, causing the cracks to close up. A polyball is a serious problem, as it can be smeared over the rest of the floor – potentially requiring screening or even recoating. Polyballs typically occur in the spring on jobs that were completed the previous winter. Here’s why:

Wood furnished from the north in winter is typically supplied at low moisture content. It is milled at around 6% MC and stored at about the same.
During winter, even in the south, humidity is at its lowest. Couple this with possible heating at the facility and moisture content can be even lower.
If the floor is laid and finished at this low moisture content, there will be considerable expansion in the spring during higher humidity. This can cause great compression of any paint or finish in the cracks of the floor.

Finish that accumulates in the cracks of the floor are denied the oxygen required for curing, and could be soft (semi-solid) when the spring expansion occurs. Facility owners and operators may be resistant to maintaining proper temperature and humidity in their facilities due to the high cost of air conditioning. Therefore, we must estimate the worst-case temperature and humidity as an acclimation condition. (On the other hand, floors laid in spring and summer will acclimate to a higher, more representative MC, thereby lessening the problem.)

Moisture Content

To ensure polyballs do not ever happen, pay close attention to this winter moisture content problem of both the subfloor and the flooring. When moisture content is low, it must be raised through the use of humidifiers or other means.

To check moisture content without a moisture meter, or if you question the meter reading, assemble ten boards and measure overall width. These boards were milled at 6%. For every 1% of moisture content over that at which it was milled, these ten boards will grow in width about an eighth of an inch. Use this guide to establish the proper moisture content. If there are open cracks in the floor, assume low moisture content. Increase the moisture content before applying the finish.

When polyballs do crop up, get to them QUICKLY. Oftentimes, these balls can be wiped up with mineral spirits if they are still wet. If they have become hard, a straight edge or a drywall knife can be used to break them off.

Everyone should maintain the proper temperature and humidity conditions in any home with a wood floor.