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We have a second-hand table with a mysterious finish.

The wood underneath is pale, possibly pine. With the finish, it's a slightly darker and "warmer" colour. The table is not antique; I'd guess only about 20 years old.

The finish is soft, so you can easily score lines in it with a fingernail. It feels slightly sticky if you just press it with a finger. It becomes VERY sticky if it gets wet, and will permanently stick to any paper left on it, so the paper can only be removed by painstakingly scrubbing it into shreds. It also turns white after getting wet, for an hour or so, then fades back to brown.

Because of the stickiness it attracts dirt horribly, and is covered in dark grime which is very hard to remove. The grime can be removed by lengthy scrubbing with a rough sponge and Flash kitchen spray, but then the finish partly comes off too.

We tried Nitromors paint and varnish remover, followed by white spirit. It made some progress at removing the finish, but left it patchy and smeary and not completely removed; I think we've had better results with Flash kitchen spray.

Can you help me identify the finish, and recommend a way to remove it properly?

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Badly applied or poor quality shellac? It's origin is bug extracted tree resin dissolved in alcohol. It's drying properties are dependent on the quality and type of tree the insects were extracting sap from. –  Fiasco Labs Nov 20 '12 at 15:20
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3 Answers

up vote 5 down vote accepted

By "White spirit", do you mean turpentine or mineral spirits? If that had no effect on it... My best guess would be that it's improperly cured polyurethane, or water-based polyurethane that wasn't mixed properly. Additionally, polyurethane doesn't take to pine well and is pretty resistant to being removed chemically, so there's another pointer in that direction.

You can try denatured alcohol. If it comes up with denatured alcohol, it's probably improperly mixed shellac.

What I'd probably do if I were you would be to sand it down completely back to bare wood, first with 80 grit and then 120 and 220 grits. I know it's a pain in the butt, but it'll provide the best finish overall. Then stain it and finish it again with something that isn't polyurethane... if you stain it, I'd recommend a lacquer finish like Deft, and then a really nice set of absorbent coasters so that you don't keep getting the surface wet. ;) Or if you do use polyurethane, use a satin spray in a rattlecan and bring it indoors to a moisture and temperature controlled environment to cure for 48 hours before you put it back into use. And your last option would be to paint it (after sanding back to bare wood, or it won't adhere!) with an oil-based enamel and a bit of penetrol.

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en.wikipedia.org/wiki/White_spirit - mineral spirits. I think if we sanded it it'd just make the sandpaper all gummy and sticky. That's what happens if we scrub it with a rough scourer, I was thinking we'd need to remove the finish, or most of it, before sanding. –  Rachael Jan 9 '12 at 7:24
    
As for what to re-finish it with afterwards, I think that's beyond the scope of the question, but personally I'd like to finish it with something very hard and smooth and impermeable, that wipes clean as easily as plastic. We already use coasters, but sometimes spills happen (we have a toddler). –  Rachael Jan 9 '12 at 9:23
    
It sounds a lot like shellac to me. +1 to the denatured alcohol. –  JoeFish Jan 9 '12 at 14:44
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It would gum up the sandpaper to start with, but eventually you'd get through it. If you really, really want to use a chemical stripper, you can try the stronger SuperStrip -- the "wood, metal, auto, masonry, and marine" one. That stuff will take off just about anything, but is a pain to clean up... make sure you get something that you can seal up the remains in, like a metal paint can, and you'll need to take it to a hazardous waste collection place. And make sure that the gloves you get specifically say they're resistant to tolulene. –  Karl Katzke Jan 9 '12 at 16:52
    
OK, I got some denatured alcohol / methylated spirits today, and it had no effect at all. The guy in the hardware store where I bought it also thought it sounded like a water-based finish, and that the only option would be to sand it. I was hoping if it's water-based it would be easier to remove, not harder; but I guess not. –  Rachael Jan 10 '12 at 18:18
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For the record, I've had some success with sodium carbonate solution, which we happened to have in the cleaning cupboard. It hasn't worked everywhere, but where it has worked it was very low effort: apply the solution with a cloth, leave, wipe off. Ended up with bare patches of wood, and an opaque yellowish solution.

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I'ld be scraping it off with a paint scraper:
One of these ones:
Paint scraper

Then sanding it down once the bulk was gone, (save gumming up a ton of sand paper)

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