Fingerprints in Finish

A cabinetmaker tries to figure out how his pieces are getting fingerprints on them. January 2, 2012

I'm noticing fingerprints (pretty obvious) in my finish while I'm assembling cabinets. We're spraying ML Campbell waterbased topcoats. We allowed plenty of drying time (it's a big kitchen). The fingerprints are light in color on the cherry. The conclusion we came up with was the prints came from the hand that had tacked off the doors before they went in the spray booth. The tacky print did not allow the finish to adhere. The only way to be sure would require bringing in the CSI crew and running the prints... not going to happen. I can mask the problem by using Old English applied with 0000 steel wool, but am concerned with the staying power of the fix. Will I be refinishing most of these doors?

Forum Responses
(Finishing Forum)
From contributor J:
I'm confused as to how you came to the conclusion that the fingerprints had been imprinted before the final coats? The finish is not adhered to these areas, or do they just look white or murky?

From contributor C:
I heard a story where employees had pizza for lunch and did not wash their hands after, and all the places they handled on the job, the finish failed. Sounds like you will need to strip and refinish.

From contributor M:
I used to fight fingerprints when I sprayed waterbase. If you touch the piece before it is tacked off, it leaves a fingerprint, then when you spray again, the new coat doesn't melt the first and you are left with your print. No problems with solvent base.

From the original questioner:
It seems like the fingerprints were put on with tacky fingers before spraying. Tack the door, put it on the pedestal, spray, put it on the rack. The prints are in classic "carrying the door" areas. Seems like the tackiness did not allow adhesion. The prints really showed up after sanding where they turned white. After spraying they disappear but slowly come back. I have never had this problem before, and we follow the typical "we're spraying today folks!" protocol.

From contributor J:
This is a shot in the dark, but maybe the tack rag is not compatible with the waterborne finish. I read that in some waterborne finishes they use a flatting agent combined with wax. Waterbased finishes have a tendency to drop their solids or flatting agents out of suspension, so they use silica (which is whitish and used to dull the coating's sheen) and combine it with wax, to keep the finish suspended longer. So I'm thinking the pressure of the fingers on the finish crushed the flatting agents and separated the wax from the silica, causing whitish defects along with poor adhesion. I'm just guessing here. That would mean that the finish hadn't totally cured before handling.

I think you should change the way you tack and carry. I would sometimes use two 4" wide boards that are connected to each other with 4" wide boards one on each end and one in the middle, and shoot brad nails up through these to accommodate the size doors being spray. With two people you could carry out 6 or more doors just sprayed (being careful not to bump and slide doors on nails) and you could spray both sides. I'd spray the backs of a booth full, then flip and set the doors down gently on the fine tipped nails and spray the fronts out, always hitting the sides both times. Some of you might be concerned with nail holes but if done right these are hardly noticeable. You can kick out a lot of doors this way and save yourself a lot of back and forth. I also tried to make something that just barely hit the edge of the door but that didn't work great.

From contributor R:
Here is my wild guess. I take it your employees don't wear nitrile or latex gloves when spraying? Perspiration and body oil is enough to screw with the finish. I always wear gloves when final sanding and between coats but I have noticed with much frustration that a drop of sweat will screw up the finish whether it's on the raw wood or between coats. The first time it happened I didn't know what the white marks were in the finish, then the light bulb went off. Try wearing the gloves and see if you still have any issues