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Oil based poly woes.

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Forum topic by NateX posted 04-07-2010 07:59 PM 1874 views 0 times favorited 12 replies Add to Favorites Watch
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NateX

95 posts in 2460 days


04-07-2010 07:59 PM

Topic tags/keywords: finishing

I never really used polyurethane until this new project. I built a book case and stained it with a water based dye stain, came out nicely. Then i tried to put on a top coat, on my 3rd try.

I have been having problems with the oil based poly top coat. No matter what I do I seem to get sags and runs. I walk away with a nice even, smooth coat and come back to runs and weird hanging sags, kinda looks like a curtain. I have already stripped and sanded this project twice because of finishing woes. This last time i thinned the poly with mineral spirits, about 5:1. It went on a little better and I certainly had more working time.

Any tips for oil based poly, or poly in general? Is it a good choice for this kind of project? How about armor seal from GF, the wood whisperer likes it. Is it a good choice for large vertical surfaces?

I have used a tung oil varnish blend over stain before and that worked well but was pricey. Trying new things sucks!

Thanks for any advice-
Nate


12 replies so far

View CharlieM1958's profile

CharlieM1958

16242 posts in 3682 days


#1 posted 04-07-2010 09:22 PM

Are you brushing it on? Brushing poly on vertical surfaces without getting runs can be difficult.

Use a wipe-on poly, or make your own by mixing it 50/50 with mineral spirits. Wipe it on with a rag. It will take several coats to build it up, but the coats go on fast and easy, and dry quickly.

-- Charlie M. "Woodworking - patience = firewood"

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SnowyRiver

51452 posts in 2944 days


#2 posted 04-07-2010 10:50 PM

I agree with Charlie…I would give the wipe on poly a try…it works very well.

-- Wayne - Plymouth MN

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bayspt

292 posts in 3168 days


#3 posted 04-07-2010 11:14 PM

I also noticed you said you used water based stain and are using oil poly. I would generally not take this risk without a coat of shellac or something in-between. I’m sure if the stain is fully “cured” it is probably ok, but I just wouldn’t take the risk. Then again, I am no finishing guru so it might all be hog wash.

-- Jimmy, Oklahoma "It's a dog-eat-dog world, and I'm wearing milkbone underwear!"

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NateX

95 posts in 2460 days


#4 posted 04-08-2010 12:16 AM

The stain looks good, didn’t move on me with the oil. I’ll try knocking down the lumps with some steel wool and thinning out the poly a little more. Thanks for the tips!

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NateX

95 posts in 2460 days


#5 posted 04-08-2010 02:10 AM

You guys are awesome! thinning out the poly with mineral spirits by about a third and using a cloth made all the difference in my project!

pics soon.

THANKS!!!!!!!!

-Nate

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CharlieM1958

16242 posts in 3682 days


#6 posted 04-08-2010 02:20 AM

Glad it worked out!

-- Charlie M. "Woodworking - patience = firewood"

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CaptainSkully

1432 posts in 3022 days


#7 posted 04-08-2010 03:03 AM

My father-in-law noticed that my alcohol-based shellac was messing with my alcohol-based aniline dye because they have the same solvent.

-- You can't control the wind, but you can trim your sails

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teenagewoodworker

2727 posts in 3232 days


#8 posted 04-08-2010 03:13 AM

don’t thin the poly… that will cause it to run more. just leave it as is and make sure that you wipe it off well… poly is made to be a very very thin coat. its not thick at all. try a good quality varnish as well like seal a cell and arm r seal from general finishes. I don’t know what kind your using but the minwax stuff is horrible,.

View Scott Bryan's profile

Scott Bryan

27251 posts in 3286 days


#9 posted 04-08-2010 01:21 PM

Glad it worked out well for you Nate. I am a little late on getting into this discussion but using a wipe on poly is what I usually advise when I see questions like this. While poly can be applied as a concentrated product it requires practice to avoid sags and runs. Diluting it with mineral spirits to form a wiping product is a good way to avoid this problem. It will take more coats to “build” the finish since this is a diluted product. But it dries quickly and several coats can be applied in a very short time frame.

And it was a good idea to make your own. Wiping varnishes are commercially available but I just do not like paying a premium price for someone else to add mineral spirits to the poly or varnish.

-- Challenges are what make life interesting; overcoming them is what makes life meaningful- Joshua Marine

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NateX

95 posts in 2460 days


#10 posted 04-08-2010 09:04 PM

The finish looks pretty good, but I want to make it better. I have heard of this paper bag trick, the one where you use a paper grocery bag as an abrasive to smooth the finish. Does this work on poly? Any considerations I should make with the cure time before I try this?

I used Varathane oil based poly, 0000 steel wool between coats. I do all my work outside and the breze blew some dust and pollen onto the finish so it’s a not glassy smooth. Darn breezy perfect spring afternoons!

Thanks again for the advice!

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Scott Bryan

27251 posts in 3286 days


#11 posted 04-09-2010 02:20 AM

Nate, the paper bag should work on the poly as well. I have never tried it but it is simply an ultra fine abrasive material that should serve to help flatten the poly topcoat. To smooth out the poly I generally wait at least 3 days after the final coat to let it cure out and then I like to sand with 600 grit to remove any dust nibs and rough surfaces.

By the way here is a 15 part video series that takes the viewer through the individual steps from initial sanding to final polishing to get a classic glass smooth finish. It is a lot of work, certainly far more than I go through, but if you have not seen the series, and are interested in taking your finishing to this level, the series may be of interest to you.

-- Challenges are what make life interesting; overcoming them is what makes life meaningful- Joshua Marine

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Ger21

1047 posts in 2595 days


#12 posted 04-09-2010 03:41 AM

Wet sand with mineral spirits to 600, then use 0000 steel wool, again lubricated with mineral spirits, and you’ll get a smoother than glass finish.

-- Gerry, http://www.thecncwoodworker.com/index.html http://www.jointcam.com

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