Troubleshooting Sanding Swirls in Pine

Softer woods can be challenging to sand. Here's advice on preventing unsightly swirls. May 7, 2009

We are doing are first knotty pine job and are getting really bad sanding swirls in our finish. We have tried different types of sand paper and different levels of air pressure with no luck. Any suggestions would be great.

Forum Responses
(Finishing Forum)
From contributor R:
Do you sand with the grain by hand after orbital sander?

From the original questioner:
Yes, it helps but doesn't eliminate them completely. My air pressure is at about 100 psi and Iíve been trying 3m gold and Mirka gold peel and stick and also Klingspor ps33 and ps35w hook and loop with no luck.

From Paul Snyder, forum technical advisor:
Soft woods and lightly colored woods are more demanding to sand well when staining. You have to move the sander very smoothly and evenly going slow enough to avoid swirls but fast enough to make production. You can't let the sander stop at any spot or it'll show up in the stain. Sand from end to end, with the grain, and overlap each pass by 50% or so. Keep changing the paper often so that everything is sanded evenly. When you put new paper on the sander, pay attention to how it feels when you move. You'll learn that feel and will know when the paper is wearing. When you're learning to sand, it's easier to sand as good as you can with the sander and then hand sand afterwards. I usually sand to 150 grit before finishing.

From the original questioner:
We have been sanding with 150 then 180.

From contributor R:
If itís the raw wood you might be rushing through the sanding procedure too fast and if itís the sealer coats 180 might be a bit too course of grit. 280 on a Porter Cable works for me for sealer sanding and 150-180 works on raw wood. Try slowing the sanding down a little and change the paper more than you have been. Nothing like a build up of sealer or sap on the sandpaper to imbed sanding scratches into either the raw wood or the sealer coat.

From contributor G:
So the swirls are in the wood - not in the finish? After orbitalling with 150, hand sand with the grain with the 180.

From contributor R:
I always drop down a grade to sand by hand. In your case sand to 180 and hand sand with 150. Make sure youíre not pushing down on the sander too hard. Also I never liked the gold colored sandpaper especially Mirka. Use the white paper.

From contributor G:
Contributor R, your suggestion is a good one. I was considering the softness of the pine may show scratch marks from 150 - which may not be a problem if they are in the grain direction. The questioner should do some tests to see what will work for him. Sia makes good white wood paper.

From contributor W:
Check out the bearings on your sanders; it may be that they are worn and need to be replaced.