Grey Pore Problem in Refinishing Jobs

When pores show up gray after a refinishing job, the culprit turns out to be insufficient stripping. April 21, 2008

We are trying to track down possible sources for a gray pore appearance in some refinishing projects. After staining and applying a sealer coat, the deeper pores of the wood have a semi-opaque dull gray look that does not deepen or brighten with greater wetting. We're bouncing between several possible causes: insufficient stripping of the old filler, residual skinning agent from the stripper, PH reaction from stripper and acid dye. We use a flow over stripping table with a mildly PH activated MC stripper. We rinse with air powered water mist, scrubby the surface with a sodium sesquicarbonate (cousin to TSP) solution and rinse again. Dry for 2 to 3 days in the heated cure area. Surface prep with 180 grit paper hand and/or power, brush and air blow sanding dust. The background stain is water aniline from Lockwood, sometimes polymerized with a WB lacquer (25% of the total solution) to prevent the stain from lifting into the SealCoat sealer. We have had trouble keeping heat (above 55 degrees) in the stripping area, which has us leaning toward the insufficient stripping cause, in that the MC is far less aggressive.

Forum Responses
(Finishing Forum)
From contributor C:
Before you do anything else, wire brush (brass) a small area with lacquer thinner and let dry, sand and spray with clear, and get back as to whether the problem persists or not.

From contributor G:
Is the grey in the pores noticeable before your finishing steps? Does this show up on different woods and does it show up in the grain of oak?

From contributor K:
Sounds like insufficient stripping to me - possibly old filler in the pores. I agree to use some lacquer thinner or acetone to try and clean it more.

From the original questioner:
So far it has been on flat cut walnut and quartered mahogany. Projects in maple and cherry came out fine. No oak in house at present. It is not obvious prior to the seal coat. The dye dries so matte that we may not be able to notice, but under the wet stain we do not see it.

From contributor C:
Until you brass wire brush the pores, you can't eliminate the other things that may be causing the problems. Do a sample wire brush, dry, sand, dye. No seal coat, just clear coat, then do another with the dye/sealcoat combo. This should let you know where the problem lies or where you need to change your steps.

From the original questioner:
The wire brush test resulted in pores stained the same as surrounding wood (no gray) under SealCoat and under gloss pre-cat.

From contributor C:
Great - then you have your answer.