Getting a glass smooth finish using polyurethane in four coats - and other tips

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Forum topic by Planeman40 posted 11-01-2011 05:47 AM 15932 views 6 times favorited 6 replies Add to Favorites Watch
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511 posts in 1506 days

11-01-2011 05:47 AM

Topic tags/keywords: varnish paint brushes

This evening I was varnishing a project and began to think of some of the painting, varnishing, and finishing tricks I had learned over the 63 years I have been building things ( I started at 8 building model airplanes). I thought I would put these on Lumberjocks. I am sure many of you experienced builders are aware of many of these, but the tyros of woodworking need to know them. I’m too lazy to organize them so they are listed as they come to mind.

How to get a glass smooth finish with varnish the quick and easy way in three coats of varnish. You will note that sandpaper isn’t used as it clogs easily and is much slower to use.

1.Prepare the wood to get as smooth a surface as is practical.
2.Apply one coat of polyurethane varnish and let dry 24 hours as the first coat soaks into the wood and dries slowly.
3.When completely dry, use a single-edge razor blade ( buy them 100 per box at the hardware store for $5 or less) to carefully scrape the varnished surface. What you will be doing is scraping away the high spots with the razor blade and filling in the low spots with coats of varnish until the finish is level.
4. Watch the gloss on the surface when scraping and be sure to scrape until there are no glossy spots. On wood like oak that have a deep grain be careful not to scrape into the wood itself. You will only be able to scrape the high spots and not be able to get into the low spots of the grain. Should you scrape into the wood, just cover with the next coat of varnish.
5.When you finish the scraping, use some OO (double ought) steel wool to rub out the finish and remove any scraping marks.
6.Paint on a second coat of varnish, let dry, and repeat steps 4 & 5. At this stage you should have a nice gloss with one more coat but with some imperfections. This may meet your needs.
7.Paint on a third coat, let dry, and repeat steps 4 & five. At this point with one more coat you should have a beautiful glass smooth finish if you painted over a wood with a tight closed grain. If you use a wood with an open grain you may have to repeat steps 4 & 5 a couple of more times until all of the grain indentations are filled and smooth.

How to PROPERLY clean a paint brush. Good paint brushes are expensive. If properly cleaned after using they will last a lifetime. After you are finished painting wash the brush in the proper thinner for the paint you are using. I prefer using a brush cleaner I buy by the gallon at the usual paint sources. If you have been lazy or stupid (yes, I have been both) and have let the paint dry on the brush, soak the brush in brush cleaner for a day or two and use a stiff brush to clean away the cruddy paint on the handle and in hard to get at places. When the brush is clean, finish by washing the brush in soap (dish soap) and hot water – this is important!!! – and end up carefully pointing and shaping the bristles like they were when still new while they are wet and relaxed from the hot water. Lay the brush out to dry and carefully store away.

NEVER dip your brush more than half way up the bristles! In fact, try to dip your brush even half of that and even less. Learn to paint carefully as if you were wearing an expensive suit. Messy painting rarely goes any faster and the cleanup destroys any time you saved, not to mention the clothes you messed up.

If painting with color, use a good primer!

A paint job is no better than the surface it is applied to. Primers properly selected can seal rosin soaked pine knots, avoid show-through of mottled surfaces, reduce the number of coats of color needed, tame wood fuzz, improve paint adherence, fill wood pores, and make for a beautiful smooth paint job. My favorite two primers are Zinsser shellac-base primer and automotive primer (yes, automotive primer).

The shellac-base primer is for wood and has a LOT of white filler, dries very quickly (re-coat in 20 minutes) sands beautifully, and builds up an extremely nice almost glass-smooth surface to get a nice high gloss finish.

The automotive primer does the same as the shellac-base primer above, however what I use is called “spotting putty”. Spotting putty is automotive primer so thick it is sold in toothpaste-like tubes and is about a thick as toothpaste. It can be bought at most automotive places like Pep Boys and places that sell automotive paint. It is made to fill in small scratches and dings in automobile finishes prior to touching up the spots with color lacquer. It can be thinned if necessary with acetone to a nice creamy consistency that can be painted on with a paint brush. I use it to fill the pores in balsa for the model planes I still build. In most cases I can do this with only one coat. Of course I sand back down until the wood begins to show through, saving weight of course which is important in model planes. The stuff sands beautifully! This stuff is great for painting small items that have a rough surface that is difficult to sand out. You can build up a nice smooth base with a few coats of thinned putty that is ready to paint without any sanding if you are careful.

Always begin by painting the hardest to get to places first. This needs no explanation.

I’m sure there are more, but its midnight and I’ve put in a long day in the workshop and I’m ready to hit the sack.


-- Always remember: It is a mathematical certainty that half the people in this country are below average in intelligence!

6 replies so far

View TopamaxSurvivor's profile


15065 posts in 2421 days

#1 posted 11-01-2011 08:11 AM

Thanks. Want to know anything I have learned in 63 yrs? ;-) It won’t be about WW or finishing ;-((

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View HawkDriver's profile


447 posts in 1378 days

#2 posted 11-01-2011 08:29 AM

Thanks for sharing, I will have to give the razorblade method a try!

-- Patrick, Helicopters don't fly. They beat the air into submission.

View crank49's profile


3506 posts in 1716 days

#3 posted 11-01-2011 02:48 PM

Ever try a real scraper?
Do you like the razor blade better?

I usually use clear sanding sealer first (well, after any staining of course), steel wool it flat then finish with the chosen topcoat(s).

-- Michael :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H

View Planeman40's profile


511 posts in 1506 days

#4 posted 11-01-2011 04:04 PM

Yes, I have scrapers and I have used scrapers. The problem I have with scrapers is you have to constantly sharpen them and then draw a new edge. With razor blades they are cheap and you throw them away when they get dull and get out a new one. I have scraped quite a number of large varnished oak cabinets to a nice gloss finish as outlined above. The process is quick and simple. And I have used sanding sealers. With the above method you don’t need a sanding sealer. The first coat of polyurethane seals the wood and you fill the wood pores with successive coats of polyurethane. Give it a try. I think you will like it.

And when you do try it, please report back here of your opinion of the procedure. I and others would love to know.


-- Always remember: It is a mathematical certainty that half the people in this country are below average in intelligence!

View Planeman40's profile


511 posts in 1506 days

#5 posted 11-01-2011 04:22 PM

Oh, and one more tip.

Use the razor blade scraper to repair dried drips and runs from painting. It will quickly level the drip/run back to the correct paint surface level. When this is done, you may work the area back to the proper gloss by rubbing with OOOO (four ought = very fine) steel wool and then rubbing the surface out with rottenstone to a gloss finish – or just repainting the entire surface again with paint or varnish.


-- Always remember: It is a mathematical certainty that half the people in this country are below average in intelligence!

View Canofworms's profile


93 posts in 247 days

#6 posted 08-10-2014 01:40 PM

I tried the razor technique and it worked well.

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