How to smooth out Polyurethane finish? - Woodworking Talk - Woodworkers Forum
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post #1 of 31 Old 11-18-2008, 01:17 PM Thread Starter
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How to smooth out Polyurethane finish?

I have recently completed my first ever woodworking project (a train table for my boys...see attached link). I am very happy with it but have an issue with the finish. I put two coats of stain on it and now have applied three coats of polyurethane with a brush. It is rough to the touch now and I am trying to get it to be as smooth as possible. The polyurethane directions say to lightly sand and apply another coat. I tried this with a 220 grit sandpaper very lightly but it almost seems as if it's taking the finish off. Does this sound like the right approach? I just tested an area and am hesitant to sand the entire thing if this is going to ruin the finish. Just no sure how to make it smooth as a baby's bottom :) Would appreciate any insight.
http://www.toy-train-table-plans-store.com/thomas-the-train-table-plans.html
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post #2 of 31 Old 11-18-2008, 01:38 PM
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You’re going in the right direction. You need to sand the finish with either the 220 you have or some steel wool (#0000?) and get the finish feeling as smooth as you can. With three coats on there already you should not have to worry too much about going through all three layers and wrecking the stain job. Just be careful. Then you need to tack cloth the surface and apply one or two new coats of finish in a dust free room. Very important that it is dust free. Let the new coat cure fully before applying the second. This should get you the results you are looking for. Good luck. Red

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post #3 of 31 Old 11-18-2008, 01:50 PM Thread Starter
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Wow, that's just great Red. I appreciate your expertise and you taking the time to help someone with a question that probably seems to simple to someone like yourself. THANKS!

If this works well and I can find the right plans my next project may be a dollhouse for my daughter. Slowly but surely I am getting a working knowledge of this stuff!
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post #4 of 31 Old 11-18-2008, 01:51 PM
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As was said, you are on the right track with the 220 sand paper. Three coats of poly should be adequate. I like to dip the sand paper in paint thinner and wet sand the finish. It gives a much smoother finish and doesn't take quite as much poly off. Once you get the piece smoothed out, you can either spray on the final couple of coats with rattlecan poly or thin down your brushing poly about half and half with poly and paint thinner and rub on three or four coats. Good luck and welcome to the site.
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post #5 of 31 Old 11-18-2008, 03:42 PM
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A few things to add to the good information above. Do not use steel wool if you are using a water-based poly. Any bits of steel you don't pickup will rust and cause problems with the finish. Be careful not to round over the edges of the table with the sandpaper. By the third coat, you should have a nearly perfect surface assuming a fairly dust-free environment. Last, if you are using a regular poly, you can do a light, final buff with 0000 steel wool, perhaps with some wax (tinted or not) to flatten the final coat and add some lustre.
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post #6 of 31 Old 11-18-2008, 03:56 PM Thread Starter
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Quote:
Originally Posted by bradnailer View Post
...or thin down your brushing poly about half and half with poly and paint thinner and rub on three or four coats. Good luck and welcome to the site.
Thanks bradnailer. I hate the spray can but was going to use a brush. You mention rubbing it on. What would you use to rub it on with?
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post #7 of 31 Old 11-18-2008, 04:22 PM
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I would use 320x light grey silicone carbide sandpaper (intended for use dry) or 320x silicon carbide (wet-or-dry) with water. I wouldn't use steel wool with either oil base poly or water based. I would use bronze wool or a synthetic microfiber pad like Scotch Brite®

I would stay away from tack rags as they can leave a waxy residue on the surface. You could brush off the piece in another room or outside, or just blow it off in an area that isn't going to be used for finishing. Applying a thinned mix of oil base, use a clean "T" shirt type of fabric and wipe on with the grain in thin coats. Don't work it around, just lay it on.

Edit: Adding wax would preclude the adding of finish.







Last edited by cabinetman; 11-18-2008 at 04:47 PM. Reason: Added info.
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post #8 of 31 Old 11-18-2008, 04:29 PM
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I found that thinning the final coat of poly (just a little) sometimes helps with smoothness. Obviously choose your thinning agent with the type of poly (water or spirits).
This is just my experience and probably not recommended by the manufacture (or my fellow woodworkers ... let me know woodworkers).

P.S. Good info on the rusting of steel wool in water based poly. Never heard of that.
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post #9 of 31 Old 11-18-2008, 04:45 PM
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All the above advises are very good... I'll just add

I learnt it from experience...First I brush 2 coats of Poly (let the fist one totally cure before the second) then...I'm sanding with 400 (if it's too rough - with 220 first and finish with 400).

As mentioned above, diluting with 50% thinner will make the Poly more "Watery" and it will spread and level itself very evenly on the surface (but I need a few more coats).

I sand between the coats with 400 or even 600 and that gives the "smooth as a baby's bottom"...

The only difference is that I'm applying the Poly with Foam brush so I don't get all this "hairs" and brush marks.

Usually, I apply 5~7 coats to build up a thick and strong finish as on the pic below

Welcome to the forum

Regards
niki

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post #10 of 31 Old 11-18-2008, 04:48 PM
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Quote:
Originally Posted by fishacura View Post
Thanks bradnailer. I hate the spray can but was going to use a brush. You mention rubbing it on. What would you use to rub it on with?
I either rub on the final coats with my hand or a very small folded up lint free cloth. If you go the rub on method, your piece will still look a little dull from sanding after a couple of coats. Be patient though, it will gloss back up.

The tack rag comment is spot on. If normally use a lint free cloth dipped in paint thinner.
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post #11 of 31 Old 11-18-2008, 09:59 PM
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I uaslly sand with 320 between coats. For finish sanding I will start at 600 and work up from their. What I end with will depend on the sheen that is needed. Refinished a dresser a few months ago and they wanted a paino finshes so, it got lots of polsing.
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post #12 of 31 Old 11-20-2008, 09:55 AM
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I probably don't need to tell you this but I'll say it anyhow. One mistake I have seen made with polyurethane, Is shaking the can to "GET IT RERADY TO APPLY". Polyurethane should never be shaken, the entrapped air bubbles causes kernels of cured polyurethane to form which leads to a rough finish. Honestly, the only time you should need to agitate your finish sealer (like poly , lacquer etc) is if you are using a finish other than full gloss. All finishes start out as full gloss and then modifiers are added to reduce the gloss level.

Ed
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post #13 of 31 Old 11-20-2008, 06:26 PM
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Another trick to give your poly a final buffing is to use a piece of grocery bag as a sanding medium. I know it sounds stupid but it works. Just tape a piece on your favorite sanding block and rub with the grain and it will "sand" out those nasty little nubs that always seems to develop on your final finish.

Jim
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post #14 of 31 Old 11-21-2008, 08:06 AM Thread Starter
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Well, I mentioned I am new to woodworking and you have all been so helpful I thought I'd reply with something to make you laugh.

So before I originally posted I had put my first three coats of poly on the train-table. You all mention dust about which I had absolutely no clue...I did my coats in the open bay of a two car garage. The other bay has the minivan which is constantly going in and out let-alone the cut grass, dirt and other things blowing around.

Now I have moved it to a "clean" room in the basement with no activity and concrete walls. Something tells me after another three coats with your advice I'll be a lot better off.
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post #15 of 31 Old 11-22-2008, 10:18 AM
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In spite of what it probably says on the can, it does help a lot to thin regular poly some as has been mentioned. But remember, you don't have to use a brush. Gels are great and you can make your own wipe on--either way you avoid the bubbles, runs, debris that lands in it. I will admit though, that it would be an expensive way to go in this instance. And don't forget about your health--don't be breathing the stuff.
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post #16 of 31 Old 10-28-2012, 02:08 AM
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What do you mean lots of polishing?

Quote:
Originally Posted by Al Killian View Post
I uaslly sand with 320 between coats. For finish sanding I will start at 600 and work up from their. What I end with will depend on the sheen that is needed. Refinished a dresser a few months ago and they wanted a paino finshes so, it got lots of polsing.
What do you mean lots of polishing? Is it just hand rubbing or applying additional coats? This is also my first experience with poly. I have learned a lot but I have lots more to learn.

Kenny

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post #17 of 31 Old 10-28-2012, 07:35 AM
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One trick I use on table tops is since i cannot seem to keep dust out, I sand with 320 go to 600, go to #0000 steel wool and then use pumice stone and rotten stone powders in a slurry. You can work it up to any finish you want that way. I usually stick to a satin or semi-gloss.
I've never seen steel wool rust/residue in my work. Not saying it doesn't happen, but I haven't seen it.
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post #18 of 31 Old 10-28-2012, 07:49 AM
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What you are experiencing with the roughness of the finish is common with any finish. Sanding it between coats just goes with the job. Each time the finish is sanded and re-applied it normally gets smoother and better. What is happening on wood is after sanding a lot of the wood fibers are just mashed down flat and when you put a finish on them especially a water based finish it stands the fibers of the wood up and get suspended in the finish. Sanding between coats brings the wood back to its original smoothness.

There was some talk about polishing the finish. I would wait a month before hand rubbing and polishing a polyurethane finish. It needs to fully cure and be hard before this is done.
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post #19 of 31 Old 10-28-2012, 11:00 AM
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Steve. Thanks on the polishing tip. I generally have gone after my finishes after a few days, but I'm guessing you are correct.
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post #20 of 31 Old 10-28-2012, 02:54 PM
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Where do u live perhaps someone has a spray setup near you I live in sw mi
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