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Getting Lots of Bumps/Bubbles in Poly

  • Posts: 40

chaplaindoug created the topic: Getting Lots of Bumps/Bubbles in Poly

I am down to the final step of finishing a hard maple table. I posted here about an issue I had with the original stain being blotchy. I sanded down to nearly bare wood and washed repeatedly with acetone to remove the binder from the original stain. I stained it with a solvent-based stain (one that just lies on the surface of the wood basically, and the stain took. Since the stain would have brushed off had I brushed on Minwax water-based polycrylic, I sprayed on two thin coats of the aerosol version of the same water-based polycrylic. This indicated that if you did not recoat within 90 minutes, then you had to let it dry for at least 72 hours. Unfortunately, I only waited 48 hours before sanding and brushing on the Minwax water-based polycrylic. I noticed some small bubbles in this coat, contacted Minwax, and they said to wait another 24 hours before sanding and trying another coat. Every coat since has had lots of bumps/bubbles in it (see photo below)! I have now sanded and recoated twice and the same result. Any ideas of how I can get a nice bump-free/bubble-free final coat?

I am using the same polycrylic, brush type, and application technique I have used on a dozen tables that came out like glass! Help! God bless.

  • Posts: 486

colin replied the topic: Getting Lots of Bumps/Bubbles in Poly

Sorry Doug ... I am out of ideas right now. I have found the Minwas folks helpful from time to time but they seem to be stumped on this one too.
Hopefully others may have an idea
  • Posts: 40

chaplaindoug replied the topic: Getting Lots of Bumps/Bubbles in Poly


Before this table top (hard maple) we have produced twenty tables, all of which had mirror finishes. Everything that could have gone wrong on this table did. I spent a month on this table when it should have taken a week.

1. Minwax oil-based stain did not take. Top had to b stripped and sanded and restained with a solvent-based stain.
2. When "washing" the top with acetone to remove the old stain, the little bit of glue showing between the boards (the boards were routed to make grooves between boards) became like gum. We had to scrape all of the gummy glue out of the grooves.
3. When I went to reapply the water-borne glaze between the grooves (to darken them), I grabbed the wrong can and brushed the solvent-based stain in instead. This got on the two coats of water-based polyurethane that was on the boards, and softened it!
4. Had to apply the aerosol version of water-based polycrylic, because the stain would have wiped off if we used brush on.
5. After putting two coats of spray-on polycrylic, only waited 48 hours when we were supposed to wait 72. Not sure if this caused the next problem.
6. When we sanded the spray-on and then applied the first coat of poly with a brush, there were myriad bubbles afterward!
7. Sanded all bubbles out tried again, got bubbles, sanded them all out, tried again, got bubbles!

Argh! Almost driving me to quit making furniture. When finishing technique that has produced twenty flawless finishes and then produces a terrible bubbly mess (by my standards) it makes me wonder if it is ME or the product. Questioning my sanity right now.

I may never work with hard maple again unless I am making a ball bat.
  • Posts: 486

colin replied the topic: Getting Lots of Bumps/Bubbles in Poly

I always say, if things go wrong at the start, the seem to go wrong all the way through ... and this table is an example of that.
Doug, I am amazed at the work you went to in trying to get a finish on this table. I can honestly say I have never seen such a complex finishing regime.

I would love to know why the bubbles keep coming back. It could be so many different things, I could only guess and likely we will never know for sure.

There is one thing I would like you check Doug, do you have a moisture meter? particularly the pin type. I am highly suspect the maple is wetter that what you might have been told when you purchased it. That could well be one cause of the bubbling which may(?) have been accelerated by the acetone.

Let me know on the moisture Doug ... I have been racking my brain for ideas and I keep coming back to green wood.

  • Posts: 486

colin replied the topic: Getting Lots of Bumps/Bubbles in Poly

Any luck getting a moisture meter to check that wood Doug ... I am interested to hear what a reading might be on it.

You should be able to take a good reading on the underside of the table top.

  • Posts: 40

chaplaindoug replied the topic: Getting Lots of Bumps/Bubbles in Poly

We delivered the top on Saturday. I had asked the mill after your suggestion about moisture level. They indicated it was kiln dried and was 7%-9% moisture level. I applied two final coats of poly differently than I normally do, and the bubbles were less. I gave the customer an option of a full refund or $100 off the top. However, the customer was satisfied and gave us the full price.

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