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Smooth glass like polyurethane

Does anyone have any tricks to get a smooth glass like finish from polyurethane without bubbles?

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Posted 2011-10-07T23:03:24+0000  by atman atman

I do a lot of polyurethaneing over oak and the thing I have found that works the best is a very good quality foam brush. I put emphases on good quality, not Wally World quality.

Posted 2011-10-08T20:19:19+0000  by macfan

Hi atman!  :smileyhappy:


Thanks for joining the community.  We hope you find a lot of information to help you out on whatever project you happen to be working on.


There are several ways to achieve a “glass like finish” when applying polyurethane.


Let’s discuss some factors that will help you during the process:  


The first thing is to make sure you are using a top quality product (like MINWAX) that will dry slow and lay out evenly.   Polyurethane.jpg 

Next is to sand between coats with smooth/fine finish sandpaper – making sure that the surface is dust free. 


Finally, a smooth high quality brush specifically made for oil finishes (like Purdy), gently pulled across the surface of the wet polyurethane will eliminate any bubbles.

                                      Purdy oil brush.jpg


Of course, the absolute best way to achieve a “glass like” finish is by spraying several coats of the polyurethane.


                                                               hvlp paint sprayer.jpg


Hope you found this helpful.



Posted 2011-10-09T13:56:19+0000  by Kevin_HD_ATL

Hello Atman,


What a great question!!!


Many of our members use polyurethane as a protective coating, so your thread is the start of a great learning opportunity!


“Old School” craftsmen were dedicated to their skill … often taking days to ensure their handy work looked perfect.


They used four basic steps to uniformly color and then clear coat:


1) If staining softwoods, like pine or maple, they would use a stain conditioner to fill deeper pockets in the grain so their stain would absorb evenly across the surface;


2) Once the color was saturated, they would wipe off the excess and allow the stain to dry overnight;


3) THIS IS THE STEP THAT ANSWERS YOUR QUESTION  They would apply a sanding sealer which “captures” the grain and makes it stand up … using a 220-grit sandpaper, they would sand off the grain that was left standing until the surface was smooth. A true craftsman would use a series of increasingly higher number sandpapers, often sanding the final coat with 1200- or 1400-grit;


4) Then they would apply their polyurethane clear coat.


The extra step, Sanding Sealer, is not really a trick, but a tried and true old school method practiced for generations by true craftsmen.


In our world today, we are sometimes in such a hurry to get done and get paid, that we overlook the lessons of the past.


Taking the time to properly prepare your wood will produce the glass-like polyurethane results you seek!


As for the bubbles, polyurethanes are made to be smoothed onto the surface, not brushed.


So, while the manufacturer does call for a natural bristle brush or a foam brush ... I recommend to my customers that they discard their usual back and forth “brush strokes” when using polyurethane and simply smooth on a coat in the direction of the grain of the wood.


Properly using a product like sanding sealer will take you from novice wood finisher to professional craftsman in one giant step!


Expect to take a little more time, but also expect the most perfect, glass-like, reflective finish that you’ve ever produced!


Now that you know "How-To," I want to see your photos and read your follow-up comments describing what you learned by using a Sanding Sealer.

Posted 2011-10-11T14:24:49+0000  by Pat_HD_ATL

I know this is an old thread... but on the possibility.... to the OP - try using a heat gun. Conservative sweeps across the finish bring the bubbles up and out. When done right, you'll end up with a mirror like finish.

Posted 2012-05-29T20:05:23+0000  by Kr4ftw3rk


If electing to use a sanding sealer, make sure that it is compatible with polyurethane. Lacquer based and sterate based sanding sealers are not compatible. A de-waxed shellac can also be used as a sanding sealer. Indeed, many woodworkers use shellac with urethanes as they feel it lessens the plastic look common to urethanes.


I have had very good luck over the years using Minwax spray urethanes. You can get a streak and bubble free surface.When spraying clear finishes, I like to place a strong light down close to the surface so that I get a glare off the surface. The glare allows me to see if I have put on an even, flowing coat. Unlike pigmented paints, it is difficult to see how evenly a clear coat is being put on.


When using spray cans, I always heat the can for several minutes in hot water run straight from the hot water faucet. This builds up the pressure in the can so that it sprays better. Oil based finishes also become more viscous when warm. They will just flow out better when warm.

Posted 2012-05-30T06:29:56+0000  by ordjen

Hello Kr4ftw3rk!


I'm not certain I understand the technique you are recommending with a heat gun.


I'm also concerned because heat guns are commonly used to make finishes release from the surface ... essentially for completely removing paint or polyurethane when you are refinishing a surface.


Maybe you could come back on the thread and provide a bit more detail about your technique.

Posted 2012-05-31T13:44:58+0000  by Pat_HD_ATL
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