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I made myself a small desk out of pine plywood and square tubing. I stained the pine with water based stain, then applied several coats of clear, water based polyurethane.

The last coat was applied at least one week after the last one, but still, the brush would get soiled with the color of the stain. I expected that to happen for the first coat, but not from the second onward. (The poly looks like diluted milk while in the can. After a few brush strokes, the brush leaves faint streaks the color of the stain when dipping it in the can)

This was at least over 8 months now, and still if water or moisture gets on the desktop, when cleaning it, the rag would get soiled with stain. If I rub the wet spot with my hand, I would get stained too. It's like this coat is not waterproof at all.

Weather here is tropical, most of the time it is between 20-35 C° (68-95 F°), it rains often but it is not terribly humid (A damp towel would typically hang-dry indoors in about 2 hours, not in direct sunlight)

Is the water based poly supposed to be water proof once cured? could it be that the stain chemically ruined the poly?

It was the first time I used W.B. poly, as now I live in a small apartment and didn't wanted to bother my family with the smell of traditional oil based lacquer. The advertised fast drying time and no odor encouraged me to try.

I'd like to "fix" this desktop, more for utilitarian purposes. If I painted over it with oil based lacquer, would it dry o.k.? (I don't think sanding the desktop would be worth the time and effort this time, as I do not own a power sander and also, this poly clogs sand paper after only a few passes.)

I already read this question: Why is my desk still tacky two weeks after finishing it with a polyurethane clear coat? but it does not directly answer my doubts, it does not clearly states whether it is water or oil based.

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    That sounds like a faulty product or one that wasn't mixed properly prior to use. I've used water-based poly many times in fairly humid environs and have never encountered this. I'd try a different brand. Minwax is reliably good.
    – isherwood
    Jul 29, 2021 at 14:34
  • I'ts been about 2 years since I did the first coats on this desk/small table and it still fits the same description. I've used Poly from the same can to cover a small MDF box painted with acrylic paint, and this time the Poly dried very quick and it became very hard (it's difficult to imprint a fingernail on it, for example). I also applied more coats from a new can to the table and it did not solve the issue. So, It seems that this particular stain/poly combination is a no-go.
    – Jahaziel
    Mar 6 at 14:55
  • That would be useful as an answer (that you could accept) if you were to specify the exact brand/type of finishes you use. That way it would be a red flag to others to not use them together. As it stands, this is simply "some finishes don't work well together" and that's a known fact but isn't really useful in determining if this finish and that finish will interact well together.
    – FreeMan
    Mar 6 at 16:39
  • @FreeMan I agree, however, I think the wood stain I used is not widely available even though it is very common in my country. This stain comes as powder in an envelope and has to be mixed with a small amount of warm water (and let cool) before use. I'll check if the label has any meaningful chemistry/composition information. The polyurethane I used is "Varathane", I think it's a very well known brand in the U.S.
    – Jahaziel
    Mar 6 at 17:07

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I suspect that the water-based finishes have never actually cured, due to your constantly humid climate. To do the job right, I'd sand the top layer down a bit and start over with oil-based poly-stain combo. Then just accept the fact that it will take a very long time to actually become dry to the touch. Unless, of course, there is an air-conditioned area you can move the desk to for a couple of weeks, in which case there is an obvious solution. Good luck.

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    The question makes it fairly clear that perpetual humidity is not the problem.
    – isherwood
    Jul 29, 2021 at 14:33

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