Dull areas in gloss polyurethane

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Old 07-24-14, 05:52 PM
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Dull areas in gloss polyurethane

I am refinishing an oak table that had a finish that was opaque with small dark dots in it. A friend described the dots as "fly sh$t". I stripped the old finish using chemical stripper, and sanded lightly. Minwax dark walnut oil stain was applied and my husband (who paints cars) sprayed Minwax fast drying gloss polyurethane. The first coat had dull spots and these spots took longer to dry. He sprayed 2 more coats thinking it would even out, but it did not. I contacted Minwax and was advised that I probably didn't get the stain wiped off well enough and some dried on top of the wood and reacted with the polyurethane making the poly dull. So I stripped the polyurethane off and started again. This time I did everything the same, except wiped the stain off with several light colored rags until there was nothing coming off on the rags. I also made sure it was wiped off within 10 minutes. The stain looked dry within 10 minutes of application. We waited 24 hours, then sprayed a coat of Minwax fast drying gloss polyurethane. In 12 hours there were dull areas again. I contacted Minwax again and they reiterated the same instructions they gave me the first time. Any ideas?
 
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Old 07-24-14, 06:32 PM
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You need to wipe the stain right away. Minwax stains have a lot of oil in them and they take a long time to dry. Especially with open pore woods like oak. I've applied Minwax stains to oak before and had stain come out of the pores after I wiped it off. I say wipe the stain right away and give it a few days before applying the poly.

You friend is right about the dark spots in the original finish. Those dots are there to simulate fly feces. This would occur is old shellac and varnish finishes.
 
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Old 07-25-14, 05:21 AM
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I also normally wipe off the excess stain within a minute or two.

How is the poly being applied? Normally you apply 2-3 coats, letting it dry and sanding between coats. It's not like automotive paint where you let it tack up and then spray again until you are finished.

btw - welcome to the forums!
 
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Old 07-25-14, 06:25 AM
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My guess would be that possibly some of the wood still had some sealer on it, (would gloss up right away) while other parts are just a little more porous. (dull down because the poly is soaking into the wood more in those areas) The porous parts of the wood will rough up a little with the application of the first coat or two of the poly. You have to sand after each coat with 220 grit and apply more poly. I'm not a big fan of Minwax poly but I guess some people have good results or it wouldn't be such a popular brand.

So if the dull areas also feel different to the touch (rough) I would say you just need to sand those areas a bit more and keep recoating.
 
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Old 07-25-14, 10:23 AM
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Thanks for the welcome!

We are waiting at least 24 hours between sprayed coats of poly, and sanding with cardboard and lightly using a tack cloth. An old cabinet maker told my husband cardboard results in a glass-like finish.
 
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Old 07-25-14, 10:54 AM
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Cardboard between coats doesn't sound like a good idea to me - the light scuff sanding between coats is to create nooks and crannies for the next layer to flow into, thus creating a mechanical bond between the layers to inhibit peeling.
 
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Old 07-25-14, 11:13 AM
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Cardboard might burnish the finish and smooth it out some but it does nothing in the way of removing any high spots [including raised grain] or help with adhesion. Generally any defects in the sheen are fixed by a light sanding and another coat. I don't ever recall having issues with an even sheen using Minwax, maybe another brand will give you better results.

I wonder if that old cabinet man had inhaled too my solvent and adhesive fumes over the years
 
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