Eliminating Sanding Swirls in Waterborne Lacquer

      Sanding issues could explain those swirl marks, but in this case, a second coat fixed it. January 19, 2012

I've been trying to find a schedule for finishing MDF with 50 sheen WB lacquer (Becker). I feel like I'm getting close to the desired finish, but very fine orbital swirls (pigtails) are showing up after the topcoat is applied. Adding to the problem, I can't even see the swirls before I laid the first topcoat down. I'm trying a combination of lights from a 500W lamp at a low angle to higher angle fluorescents to check for the defects. My final sand before the topcoat is with 400g on a Festool rts400 (5/64 stroke). I was wondering if a linear stroke sander would help solve my problem?

Forum Responses
(Finishing Forum)
From contributor M:
I used to have problems with swirl marks. I did two things - stopped using Festool sanders and switched to a Dynabrade and started using quality sandpaper. No more problems. I tried a lot of things, but it boiled down to the Festools and the sandpaper.

From contributor J:
Try just hitting it by hand with a fine grit sponge. Doesn't take much to knock it down before applying the topcoat.

From contributor C:
Might be spraying too thin of a coat or overly thinned. If you're sanding with 400 and a 5/64 swirl and seeing them, I say a heavier coat will fix it.

From the original questioner:
That's exactly what the problem is. I hit them with the second coat and they vanished. Thanks a lot - great help.

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