Wave pattern throughout refinished hardwood floor

Q: Thanks for allowing us to write questions to you. I just had hardwood floors installed in 3 rooms of my home, and asked them to resurface the kitchen and hallway which already had hardwood. After 3 days, I entered the home to find that there was a wave pattern throughout all 4 rooms, now even on the one that didn’t have the problem originally.

I called the contractor, and he saw the pattern (which runs perpendicular to the direction he sanded: the length of the boards). He told me though that he didn’t know what caused the problem. He has been in business for over 20 years, and this was hard to believe! I thought that maybe putting a satin finish on top would reduce the visual effect of the waving. He said he couldn’t guarantee sanding would fix it or the satin finish (he originally used semi-gloss).

He used a machine that uses 22V, and it is a belt sander. It’s hard to understand how the pattern could be so cyclical perpendicular to the direction he sanded. How can irregularities in the machine cause the waves to line up perpendicular to the direction he sanded? Not intuitively obvious.

Thanks for your consideration in answering my concerns.

A: There are a couple of issues that from time to time can cause issues in sanding floors. One is more severe than the other. One has a likely cause from vibration. The other is more than likely an equipment issue. The lesser issue is called chatter which denotes very fine, closely spaced ripples. You can see this at times on lumber you purchase because the board vibrates as it goes through the planer. The more serious condition is indeed called the wave, is much more pronounced than chatter and is spaced much further apart, say every 8″. He may have had some debris on one of the sander wheels so that with every revolution of the wheel the machine gives a slight shudder. Or he has an issue with his drum, pulley’s or shaft. The only way to eliminate it is to completely sand the floor again with the initial sanding being on an angle of say 20 degrees or so to flatten the floor. If the floors were simply sanded in the direction of the wood the drum on the sander would simply follow the contour of the floor and the wave would get worse.

Similar Q: Wondering whether chatter or waves.. can I send you a picture? The company installed new wood in some rooms and tied in to existing wood. All have these marks now. They redid the floor, taking off a very thin layer. I could not feel any difference to touch. It looks better, but the marks are still there.

A: You can send a picture. Chatter are like little ripple lines closely spaced. Waves are more like 10 inches apart. Chatter for the most part is not severe and for the most part is a vibration issue. the wave is more likely an equipment issue.

[after seeing pics:]

This is not chatter which is spaced very closely together like ripples. This is it’s cousin it looks like to me. This is called ‘the wave’. There is likely some issue with the sanding machine. It could be debris on one of the wheels, something out of balance with the drum or pulleys. Notice how the dig marks are fairly evenly spaced. So there is a shake which occurs at the same intervals. Aside from correcting the problem with the equipment to remove this the floor has to be sanded first on a bit of an angle, say 20-30 degree. If they just go straight up and down the floor the drum will simply follow the existing contour of the floor and these marks will become more pronounced.

One thought on “Wave pattern throughout refinished hardwood floor”

  1. It is actually caused by “Frequency Resonance”. Likely this is on a first floor level over steel and I-Beam subfloor construction and not the machine…exactly. I bet that machine will work fine anywhere else. I am writing a detailed Blog on this matter for Wood Floor Business Magazine. Simply…the floor sander resonates at a frequency that syncs with the frequency of the floor. This is a harmonic or sinusoidal load (vibration) much like if you have ever been stuck on a bridge in heavy traffic you will feel the bridge vibrate steadily. Proof is that when you change the angle to sand…the wave stays the same or even gets worse. The only solution is to use a rotary sander which will not have the same frequency. I have several photos and “recipes” to repair. I’ll copy you when the Blog posts. Something new to add to your hardwood portfolio. many flooring contractors spend a fortune tuning their machines for wave only to find it still happens. It’s the subfloor system on this one. SD

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