Wave pattern on sanded floor

Q: I just built a new house and my floors on the first floor have a consistent wave in them that you can only see if light is shining on it. The contractor at first said his machine was broke; so, he did it again and got the same result.

Now he thinks that the floor isn’t sturdy enough and has too much bounce. Could that be possible? Or because the machine was broke the first time, the floors can’t be repaired? He sanded them a third time and nothing changed.

A: If there is a problem with a sanding machine and it leaves waves, the only way to get rid of them is to cross cut the floor first. If we keep sanding in the same direction the drum will simply follow the contour of the floor. Was the floor cross cut the second and third time?

There has been much debate as to what causes this issue. I don’t think there is one simple answer. Even a small fleck of something stuck to one of the side wheels on the sander can make it limp and hence create a wave. If the sub floor was not solid enough, I would suspect the issue would probably be chatter, which is a slight ripple that is very closely spaced.

Related Q: I just had my floors sanded and stained, but after a second coat of poly I’m noticing a repeating pattern of two inch lines running across wall to wall perpendicular to the direction of the floor. A repeating pattern every two or three inches, light-dark light-dark. Almost as if a wave pattern displayed as light cast across surface. It’s not visible from all angles.

A: It sounds possibly like something called chatter. Either an issue with the sanding machine or even from vibrations in the floor while the sanding was being done. The lower the shine of the finish the less noticeable it will be.