# Air Bubbles after finishing Stair Treads with Polyurethane



## water_cutter101 (Sep 8, 2009)

Hello All,

I have a small problem and wanted to ask some advice.

I purchased a new set of treads and risers for my stairway.

I just finishing staining and putting 3 coats of floor grade Polyurethane finish on all of it (satin). I used a good quality natural brush for this DIY. The polyurethane is oil based.

For the most part they look good. I sanded with 220 grit between coats and each coat had less bubbles than the last and was even more smooth.

The problem is that even after the 3 coats there are a couple of air bubles here and there (maybe 4-5 small ones per tread). I'm not sure if that's normal or if there is a way to do a last coat (maybe a different method) to make it all smooth.

I was thinking of a very light final sanding, diluting some polyurethane with mineral spirits and rubbing on a final coat with a lint free cloth (or similar).

Any suggestions? Should I just sand the areas and wipe on a bit in those areas where the bubbles are or just leave it alone because it's normal.

I can't say I've really taken a close look at stained stairs at other peoples houses so I just don't know.

When I went shopping to see how much they were already stained and finished, all the samples were flawless, but maybe the makes sure that all samples are perfect.

Any help would be appreciated.


Regards.


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## phinds (Mar 25, 2009)

My own experience w/ poly is that it gets air bubbles pretty easily and the only way around it that I have found is to use lots of thin coats instead of fewer thicker ones. That's not much help to you since you've already put on the thick coats, but good advice for the future.

For now, I'd say sand down the affected areas and apply thinner coats.

Another very annoying problem I've had w/ poly is that coats don't always adhere to each other very well, and over time you can get some flaking of the top coat (again, this is only if you use thick coats).

Good luck.

Paul


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## LouLewyLewis (Sep 2, 2009)

Phinds , very good advice , and I'm impressed . I've bookmarked your web site for a later date to look at, but a quick scan that I did do, well like I said I'm impressed . :yes: :thumbsup:


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## water_cutter101 (Sep 8, 2009)

Paul,

When you say the "affected" areas, do you mean just the area with the bubble? Is it ok to sand just the bubble area and then brush poly locally in one area?

I did apply thin coats for all 3. I tried to avoid the "pooling" on the wood. I even experimented prior to the job on some samples and found the bubbles were there whether the coats were thinner or thicker.

Thanks for the advice...

Regards,
Joe


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## phinds (Mar 25, 2009)

Joe,

If you are using thin coats, then the problem is likely that the wood is red oak, which is notorious for this problem because of the extreme porosity. 

The sanding doesn't need to much exceed the area of the bubbles, and use a grit that leaves very fine scratches in the surface as opposed to trying to get it totally smooth before the next coat; poly adheres best when you do it that way and the scratches dissappear (filled in by new coat and too small to cause surface indentations in new coat).

One annoyance I've had with localized application of poly is that sometimes the edges of the new application area take on a cloudy look and the only way I've found around it is a smidgen of luck and some very light strokes with a foam brush (and sometimes brushing from the old area back into the new does the trick) --- it's that or redo the whole surface.

Paul


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## water_cutter101 (Sep 8, 2009)

Paul,

Yes you are correct, it's red oak. You certainly know your stuff. Even after 3 coats, the entire surface is still not 100% smooth. There are some areas you can still make out a "terrain" (in very dark spots) on the wood. It looks like I would have to apply several more coats to smooth out the entire surface. I don't think it's worth it.

Overall, I think it's still good. After inspection today (24 hours after last coat), there are probably less than 4-5 very small bubbles on each tread and more like 2-3. Unless someone puts their face down on the board it would be a little hard to notice.

I'm VERY picky (it's a probably a curse) so part of me wants to do a 4th coat with some diluted poly with mineral spirits. On the other hand, my wife is saying "just get the job done", meaning "it looks fine and install the new steps/risers".

It's just getting over the idea that everytime I walk on the new steps I think to myself I could have put another coat on.... now it's impossible to do it (or at least not practical).


Regards,
Joe


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## trident98 (Mar 7, 2009)

I always use a "sanding sealer" first coat. Use the same brand as the poly. The sealer helps to seal the pores and gives a uniform base for the poly. I've not had any problems with bubbles. Like the others before me stated, thin coats. Use a 400 grit or 0000 steel wool between coats. Use a "tack cloth" after sanding to remove the dust. hope this helps on future projects.


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## Streamwinner (Nov 25, 2008)

You can also thin poly with mineral spirits, as much as 50% (I usually aim for about 10%). I have found that this greatly reduces air bubbles, even when I'm in a hurry and brushing quickly (also won't pool). Of course, then you have to do more coats, and finish with a full-strength coat.


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## Buzz Saw (Dec 28, 2009)

The "perfect" finishes you see were applied by spraying. If possible, spray on your last coat. 
If you only have minimal bubbling, don't worry about it. You said you never noticed it on other stairs, so no one is going to notice it on yours. 
Being too picky is a problem for me, causes me to waste too much time when I could be moving on to other things. I always stop to ask myself, "does this really need to be museum quality?" The answer is usually no.
Do your stairs that are going to be constantly underfoot need to be perfect?
This is not to say that Zen finishing isn't self-satisfying in and of itself. It is very much so, but in most cases, it's not needed.
Ciao


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## my-woodwork-future (Mar 17, 2010)

Hello everybody..I just registered now. I come from the automotive refinishing and have no experience with wood, but ther are a whole gamout of reasons that causes blistering, bubblling, blowing and bubbles, etc.. Whenever we had air bubbles under the paint coats or under the urethane clear coating were caused mostly by solvent creating a bubble then popping out. That is solvent trapped under the layer of paint, If you applied a too heavy coat or overly thinned , then you need to allow more time for the solvents to evaporate between each coat. Also, the best cure is from inside out, but if you fanned or expose it to the sun, the outside layer of the paint will cure faster that the bottom layer, or abrupt changes in atmospheric pressures, use of wrong thinner or reducer, insufficient drying times between coats or too heavy applications the evaporating solvents or even, humidity on the air, wich will escape later thus resulting in a layer of air bubbles or tiny blisters.
Is much better to paint on a dry day with low humidity, because humidity is also a factor that will create air bubbles because air moisture can be trapped under the film


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## Just Bill (Dec 29, 2008)

Was the poly stirred, not shaken?? never shake poly water or oil, you will get bubbles.


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## water_cutter101 (Sep 8, 2009)

Thanks for all the great advice....

In the end it actually worked out very nice. I think I mentioned before I am very picky and when up close to the step I would get worried about imperfections. Now that they are on, you can't even see any of the imperfections. It all just blends right in.

Anyone that has come over and looks at the steps is shocked that I stained and finished them myself.

I guess I was worried for nothing. However, next time I will use glossy, not satin.


Thanks again!!!

Joe.


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## kostek (May 11, 2009)

A thought
How about another sand over the affected areas, then use a touch up gun to spray another coat.
Actually, I am thinking of doing my entire staircase with a touch up gun.


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## water_cutter101 (Sep 8, 2009)

It's funny because it's been about 4 months since the stairs were installed.

Just before they were put in I was all upset and was willing to do anything to make it better.

Now that it's in and we've been walking all over it for quite some time I don't even think about it anymore.

Also, everyone that comes in the front door says they love it. They don't bend down and pull out a magnifying glass and look for flaws.

I'm glad I didn't do any further work. Life it too short to worry about the little stuff.


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## Colt W. Knight (Nov 29, 2009)

I switched from using poly finishes to shellac and lacquer. I am much happier with my finishes now. Seemed I was always running into to some sort of trouble with poly.


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