Refinishing table, Water-Based Polyurethane Dries Fast and Leaves Blush after Sand. What to do?

Question

Here are the facts:

• Pine table
• I applied a wood conditioner at the beginning.
• I stained in the garage with the garage door open.
• Super high humidity now.
• The water-based polyurethane dries super fast.
• I used a water-based polyurethane on it and when it dries, it looks nice and glassy but when i lightly sand, it leaves white spots (I think this is called "blushing").
• I can apply the water-based polyurethane again and the spots disappear, however because of defects like a bubble, I have to sand it and I get the blushing all over again.
• With one application, I tried applying very slowly to minimize bubbles and it worked, however I would get brush marks because of the quick drying.
• I sanded w/ 220 grit with my orbital sander on the slowest speed to try to even it out as much as possible. I'm still going to sand a little tonight since some poly drops showed up. I don't want to pierce the polyurethane.
• I was at a paint store and I don't think the guys knew what they were talking about, however some old guy that was a customer there told me that if there was a gentle breeze that could contribute to my problems.

I want this to look amazing at the end: nice, smooth, and glassy. What should I do about the white fogginess?

Answer 1

The blush is precisely because you're sanding. You're taking the nice, smooth, shiny surface and putting millions of tiny scratches into it.

You have identified your own problem: As you indicated a slower application rate allows you to eliminate the bubbles and that eliminates the need to sand, but it's drying to fast for you to work slowly. So, you need to make some changes to your application setting:

• Wait for cooler, drier weather.
• Work indoors where it's cooler and drier (assuming inside is air conditioned).
  • Make sure you still have adequate ventilation, but a water based product shouldn't be too bad. Read and follow the instructions on the tin.
• Buy a poly that has a slower drying time.

Any one of those 3 should help significantly.

Do not use a power sander, even with 220 or finer grit. A machine is going to take way too much off way too quickly. Unless, of course, you're trying to remove most or all of the coating.

When applying the poly, you should only need to sand if you're planning on adding another coat. The sanding (220 grit or higher, by hand, very lightly) is designed to give a "key" to the existing surface for the new layer to stick to. It has the added benefit of knocking off any bubble or nibs (bits of dust that settled on the wet surface).

Once you're satisfied with the surface you've got, STOP! There should be no need to sand your final coat.

Answer 2

How long are you waiting before sanding? How many coats of poly? Perhaps you can think about buffing rather than sanding. Even just with a couple layers of cloth under your orbital sander. I've had to use quite a few coats or poly or spar urethane in similar jobs. Even if it looked dry, I remember needing to wait longer than I wanted to before sanding - especially if RH is high.